YouTube Transcript:
Java Tutorial for Beginners

foreign
and in this video we're going to talk
about core Java in this particular
course which is a lengthy video you're
going to learn everything from the
basics of core Java to the end of core
Java now this is not the first time I'm
uploading the video on Java if you can
see from last few years you will find
multiple Java playlist and multiple Java
full-fledged video but we all know right
the quality of videos are going up every
day plus the number of features being
added to a language is going up and
that's the reason I'm going to re-record
the entire course now this is a
full-fledged course and that's why it's
so lengthy but you cannot finish the
entire course in one day even if it says
12 hours or 13 hours it will take time
now let's talk about Java now why Java
is so famous now if you see the
programming index the top five
programming language you will always
find Java there maybe at the first
position or at the fourth position you
will find Java why Java is so famous is
because Java has multiple features which
helps it to be used in the Enterprise
Market I mean not just Enterprise Market
it can be used for mobile development
web development and of course Enterprise
application and most of the big
companies if you go there they are using
Java as their preferred language now in
Java we have a technology called jvm and
it's not just Java we have multiple
languages running on jvm so even if you
are working on some other language let's
say kotlin Scala groovy ultimately
you're working on Java technology and
that's why if you learn core Java it is
much easier for you to jump to different
languages and I've also observed
irrespective of which entry you are
going for it can be for development or
testing and that doesn't matter which
language your working on that maybe
python C sharp C plus plus they might
ask you Java questions because because
most of the interview questions are
based on Java because they feel that if
you know Java that means you know other
languages as well or you can learn other
languages easily as for my experience or
did I forgot to introduce myself uh my
name is Naveen Reddy I'm a corporate
trainer software developer and currently
focusing one on blockchain but Java is
my first love so I'm working on Java
from the last 12 years I've made
multiple courses on Java on YouTube and
different platforms and yeah I can teach
Java any day anytime
yeah sometimes I have to watch my own
videos to realize the concept but the
thing is I love Java and with this
experience I'm making the entire course
I was talking about my experience right
in fact I have learned multiple
languages in this all 12 years maybe I
have worked on 12 different languages
you can name it maybe C plus plus C
python Java JavaScript uh go language so
I love most of the languages some
languages are learned just for the
projects but then when I was learning
those languages I was I was feeling hey
it's it's so easy it's because
I have learned Java yes people say Java
is difficult just to start with it is
difficult maybe if you want to learn
Java as your first language it's kind of
difficult because if you're coming from
other languages let's say python or
JavaScript and if you want to print one
statement you can actually see that in
one line uh that's not the case with
Java right you have to write five lines
of code but yes once you make a big
application the number of lines will
remain almost same okay so Java is
difficult yes just to start with but the
thing is Java is one of the most
readable language what I mean by that is
if you are looking at someone else code
you can read the Java code line by line
uh that's not true with other languages
okay so Java is great in that terms Java
is maintainable and that maybe that's
why they most of the industries are
preferring to use Java now Java has
multiple features we'll talk about those
features later but just to name them we
got Voda which is right once one
anywhere which supports multiple
multi-threads it has a collection API
concept you can handle the exceptions
and we are going to learn everything in
this particular course now just to go
for the history of java Java was made in
1995 by sun microsystem and it was led
by the team of James Gosling later on
Oracle bought Sun so now the trademark
of java belongs to Reichel yes in
between Oracle did some messed up things
with Java but yeah they are back on
track and the beauty is Java is getting
updated every six months not the major
updates but they are working hard to
make Java as the most powerful language
so I hope you were excited for the
entire course we are going to start from
the basic as I mentioned and you will
learn a lot of Defense stuff but as I
mentioned it's not about completing the
entire course in one day you can use a
timeline to jump between these sections
and also with this we also have a code
there so in the description you will
find the link GitHub link where you can
access all the codes and maybe it will
help it will be helpful for you to write
this code so let's start the journey I
know you were excited to write your
first Java code but the thing is to
write the Java code you need a place to
write the code right so basically you
need a editor of course notepad works
right we all love notepad apart from
notepad we have multiple softwares using
which you can write your Java code maybe
you you can use wordpad or you can use
notepad plus plus you can use edit plus
when it comes to programming there are
multiple editor options available
specifically for Java the one of the
most famous IDE now IDE stands for
integrated development environment so
basically we have editors where you can
only type the code or you can use a IDE
where you can type the code we can where
you can run the code where you can
compile the code where you can debug the
code and you can do everything in an IDE
now which is good now for beginners
using editor makes sense but then if you
are working on a real project you can
use a IDE now it is depend upon you
which idea you want to use in this
course we are going to use vs code
now there are multiple options available
we have Eclipse IntelliJ IDEA we have
netbeans in fact I have worked on a lot
on netbeans I just start off my career I
have worked on Eclipse as well for some
few years and then I've worked on
intelligent idea of one or two project
my personal favorite is intelligent idea
the only thing is the ultimate version
which is awesome is a paid version the
community version is good but it has
some limited features
now why we are using vs code is because
it's a very lightweight editor or an IDE
so you can do everything in vs code and
it's also lightweight
okay apart from that you also need a
compiler right so of course that when
you write a code of course you have to
compile your code so that your machine
can understand that and in terms of java
we have to download jdk which stands for
Java development kit now how do you get
these two softwares it's very simple
just go to your browser and search for
jdk download and also you can search for
vs code so these are two softwares we're
going to use
let's start with JK first in jdk we have
two versions We have a propriety jdk of
what I call and we have a open source
version in fact there are multiple
implementation for open source you can
choose any of them uh we have collector
we have different implementation you can
just export them but I'm going to use
Oracle jdk here yes at one point Oracle
made a Java paid but now it's free again
so we can use Oracle jdk here and you
can just click on the Java downloads
and you can see it will give you
multiple options the thing is
at the point of this recording Java 19
already launched Java 20 is going to
release soon and with every new version
in fact Java is following this six
months uh updates now so every six
months you will get new updates right so
with every new update you will get some
features but the basic language will
remain same so irrespective if you are
watching this when we have Java 25 don't
worry Java is Backward Compatible and
the basic language features will be same
of course W minor 2x in the new updates
new features
but overall it will be same in case if
there is something new happening which
is changing the basic concept uh we are
going to re-record that video in the in
this series
okay now which one it wasn't to choose
here should we go for Java 19 or Java 17
the thing is with every six months you
get new features right but not every
version is LTS LTS stands for long term
support so there are some versions which
get long-term support now Java 17 is one
of them so instead of downloading Java
19 we are going to go for Java 17
because it's LTS
so if I click on Java 17 here
and you can depend upon which OS you are
using I'm using Windows here or for the
kojo we are going to use Mac OS but then
the setup will change but the underlying
software will remain same the code will
remain same right so irrespective of
which OS you are working will not make
any difference for for the course
but for this video I'm using Windows
here and if you're using Linux you can
choose Linux distribution or Linux
package here
if you're using Mac OS you can download
Based on is it a mac Apple chip or it is
a Intel chip
and you can go for Windows as well if
you're using Windows and for this
machine I'm using Windows so you can
click on this download here and it will
take some time for the downloading
this setup is actually very simple you
just have to change one thing which I
will show you in some time and
straightforward in Mac
uh in Windows you have to set the path
okay we'll see how to do that
next is vs code and you can just click
on this download here now first of all
vs code is a very popular IDE now if
you're coming from some of the languages
you might have already used vs code so
it's quite easy
okay now depending upon which OS you are
using you can download one I'm using
Windows here I will click on download
and yeah it's starting soon and you can
see it is downloading here
now let's start with the jdk first when
you click on jdk
uh it will take some time the thing is
in my machine I already have this two
softwares so the first screen might
might look different for both of us
you can see from it says reinstall I
will say yes so here you can see it says
next in fact for you as well you have to
just click on next next everything is
smooth and depend upon your machine
speed it will change
the speed might change
okay that's jdk install but how do you
verify if you have jdk okay we'll do
that in some time but let's do the setup
for vs code again straightforward setup
uh say I accept you don't have a choice
here you can say next next
um
nothing to specify just body fight will
be there so just keep it and install so
by the time it is happening what I will
do is I will open my command prompt and
how do you check if you have Java
installed so go just type Java
hyphen hyphen version and it will give
you the Java version if it is coming
that means Java our JK is installed in
fact you have to check one more thing
which is Java C version for the compiler
and you can see it is getting giving the
version here but in case if you get
error that the Java C command not found
even if you have installed it that means
the path is not set how do you verify
the path here
it's very simple actually or you can
just go to search and search for
environment variables or if you type
environment it will give you the first
font just click on that and here if you
can see we have an option of environment
variables just click on this environment
variables and you can see we have user
variables path here you have to make
sure that you have a path variable or
you can edit times in system variables
if you want this to be applied
throughout the system different users
then you can use system variables or you
can use a user variable here
I will go for system variable make sure
that you have path in case if you don't
have a path click on new and set the
variable name as path and set the value
now what is the value here now the value
is your bin folder so what you can do is
you can go to your C drive go to program
files search for Java here you can see
we have Java and open this jdk click on
bin now this is a path because inside
this bin you have Java C so copy this
and you can paste it here in the
environment variables value
now since I already have pathway table I
will not create new if you don't have a
path variable create click on ok but I
will not do that because I already have
a path variable just double click it
it will show all the path variables for
my machine I already have it here if I
don't have it find the empty place or
click on new
paste and you're done
and click on OK for me it's only this I
will just remove this
and click on ok ok now once you do this
setup you have to make sure that you
restart your CMD
and now try for
Java C version and it works okay so
that's how you install jdk and make it
work now let's open vs code now once
your vs code is installed
you can see it's done for me I will say
launch so that's how vs code looks like
now this is a place where you have most
of the settings in fact I have already
used vs code in my machine with
different extensions and that's why you
can see them here but for you I don't uh
you will not be having this extension
you will be having only first four uh
now how do we check if everything is
working just click on Terminal here new
terminal
and try to do Java C here as well and it
works so your jdk and vs code is all set
now you can start the code now once we
have our setup done it's time to write
our first code that's right so finally
we are going to run our first Java code
here now for that we have to open our
editor so of course in the last video we
have discussed that we are going to use
vs code so let's open vs code here so I
will say code okay so our vs code is all
set to write our first code you can see
it will give you a welcome screen when
you do it and then it will ask you the
preference do you want a light color
dark color dark high contrast or light
high contrast I would say go for dark
because it's good for development it
will launch train your eyes at least so
let's close this get started and this is
how your vs code will look like okay
simple stuff right now what we'll do is
first of all uh where you will get your
folder so you will see your folders on
the left hand side so this is where you
will get your project all the files
which you want to work with so you'll be
having that here now of course in the
upcoming tutorials we'll be using a
different IDE and I want you to get used
to different IDs when you work with so
on the left hand side we can see we have
an Explorer here and then we if you want
to search something we have it here if
you want to add some extensions which we
are going to do later uh we'll add
certain extensions to work with at this
point we don't need any extension so
just keep it blank I mean no need no
need to install anything here in my
machine I already have something on some
other accounts but on this account I
don't think so anyway and then if you
want to run and debug debug you will
find the option here now why do we run
of course we know what to why to run
right but why do we debug the
application yeah we'll see that later at
this point let's open our files of
Explorer here and this is where I want
to create my first project now how do we
create a project now project will be a
very broad term at this point what we
are going to do is we will create some
files and of course when you merge these
files and libraries you create a project
at this point we do are not working with
any external libraries at this point we
are just going for a simple files okay
hello world right so for that what we'll
do is we'll click on open folder because
all these files will be part of one
particular folder so we'll click on open
folder and it will give you certain
options where you want to save this so I
will save this in on my desktop itself
okay in fact on my desktop I want to
create one more folder so I will say
open folder again inside desktop I would
I want to create a folder here we'll say
this is I will have a short name so it's
a course create and open so you can see
we got our course folder here what I
will do is I will zoom in inside my vs
code so that you can see everything
properly and again the recommendation
would be to watch this on a bigger
screen so that you know you can actually
understand each and every line because a
mobile sometime you will be seeing a
font size and a small font okay I don't
want to welcome I don't want to see this
page every time I open my vs code so I
will just uncheck this and click on
close here and let's create our first
file and this is where your going to
write our first code right so we have
already seen how do we install jdk how
do we check the version on the terminal
can you do that in this so vs code
itself has a terminal here so you don't
have to open the external terminal of
course if you are using Windows you will
be having an option of command prompt
but let's click on Terminal here and you
can see we have an option of terminal
click on this one
okay this is where you can enter your
commands whatever commands you have the
same command will write here so we'll
say Java version and you can see I have
Java 17 in this machine and Java 18 is
already released but then Java 17 is the
LTS version so when you say LTS it means
long term support right so we'll use
that and we'll also check if my Java C
is working you can see javasa is also
there now Java C basically stands for
Java compiler as we discussed before so
we need both we need Java to run the
application we need Java C to compile
the code right okay cool so we got the
terminal as well I will just minimize
this a bit okay so now let's create our
first file so what we are going to do is
we'll click on this particular file here
and we'll name this as Hello dot Java
now this is something you have to
remember whenever you create a Java
project you have to make sure that you
give an extension or Java files
basically you have to give an extension
with DOT Java now different languages
have different extensions and when you
talk about C we say dot C when you say C
plus plus language we say dot CPP when
you say JavaScript we use dot JS in the
same way in Java we say dot Java simple
stuff right so you got our file here now
vs code will give you some suggestions
will ask you to install some extensions
for Java and we'll click on
recommendation okay it is asking us
tension pack for Java which will help us
it will give you some options and extra
stuff again this is just an advantage
which you get from vs code again not
required if you don't want to install
this extension I think I should go for
it or we also have intelli code for AI
assistance but yeah we'll stick to this
extension again in your machine you
don't have to install this there's no
compulsion you can still write your Java
code but maybe it will give you some
suggestions and stuff in between let's
see let's close this and let's write our
code so extension will be installing
behind this thing you don't have to
worry about it so basically how do we
write our Java code it's very simple
actually uh first of all the question is
what you want to do in this code do you
want to create a game or do you want to
build a rocket which will go to mass
they will not be doing those extra stuff
what I will do now is I will create a
very simple file which will print hello
world I know that's how you start a
programming language so it is
irrespective of which language you're
learning the first thing you do is you
print hello world so here I want to
print hello world now how do we do that
see uh if you in case if you are coming
from other languages let's say python
right so what you do is if you want to
print hello world in Python you can
write only one line and maybe Java is
not that famous for Simplicity at the
start of course when you build a bigger
project Java is much more structured
compared to the languages but then to
start with it's not that easy so just
bear with me okay so what we are going
to do now is if you want to just
experiment with Java if you want to play
some if you want to test some code or
stuff we have an option which was
introduced in Java 9. so basically you
can write your code in one line you can
get the output example so even before we
jump to hello world let me show you
something so so we have we have a
concept of J shell in Java so it was
introduced in Java 9 as I mentioned so
you can open your terminal and here let
me just increase the size a bit so what
I will do is I will click on J shell or
I will type J shell and it will give you
a j shell prompt okay now J in this case
is Java so you can it make it should
make sense now okay so what you can do
in Json is if you want to experiment
something example why do we write code
why do we build applications so to solve
problems right now it can be a very
simple problem as well example if you
want to add two numbers it's very simple
you can say two plus three and if I say
enter you can say we got five right so
we got the answer which is five what if
you want to do a subtraction you can do
that so 9 minus 6 and you can see we got
three so this is working but what if you
want to print something so in this case
what you can do is whenever in Java if
you want to do something we use
something called Methods at this point
you don't have to remember methods on
what the definition is just remove that
there is a concept called Methods using
which you can do something the only
thing you have to remember is if you
want to do something you need methods in
the same way if you want to do something
here I want to print something right so
we have to use a method called print it
is a inbuilt method in Java so you don't
have to worry about it just use it it
will work so whenever you call methods
you have to pass the values so I want to
say hey print but then it will say okay
I will print but what you want me to
print so you can mention that in this
blanket so in this round brackets you
can mention I want to print hello world
now if you want to just print a number
let's start with that first so let me
just print a number which is six and uh
in Java there's one more thing you have
to put a semicolon at the end it should
work in this but then remember this at
the end put a semicolon that's how you
mentioned hey something is getting ended
so we're going to semicolon there and
now what you can do is uh let's try to
run this code now adults right adults
are very important in your life in your
program in life basically you still got
there it says cannot find a simple call
point it's not working okay cool no
problem so let me just clear the screen
now clearcom is not working ignore that
you will say so let me open JSL once
again and let's because I just want to
keep it on top so what I will do now is
if I want to print something and I want
to print a value 6 at the end I want a
semicolon as well now Java says if you
want to call print print belongs to
something right so it when I say it is
available inside Java so the statement
you have to always mention is system dot
out dot println see there will be a
point where you I will talk about what
is system what is out at this point it's
very difficult to understand so just
bear with me this is a statement which
you have to re which you have to use if
you want to print something on the
console okay so if I want to print
something here just say system.out.print
and whatever value you want to pass say
enter you can say we got 6. but what if
you want to print hello world I don't
want to print six so if you want to
repeat the same statement of course you
can type or you can click on the up
Arrow it will give you the option now
here if you want to print hello world
you have to put that in double quotes so
whenever you want to do something with
text see numbers are easy to use you can
simply say six but if you want to work
with a text you have to put that in
double quotes the way I've done it here
so in this double quotes you have to
mention hello world right that's how you
start a programming programming Journey
right I will say enter and you can say
we got hello world what if I want to
print something else which is very
simple you can say double quotes not
been ready the Disco and if I say enter
you can see we got the text so whatever
you want to print just put that in
double quotes and it should work and you
can see we are getting the output as
well so cool so we are able to do this
with the help of J shell but will it
work in this if I try to copy this in
fact why to copy when we can type it so
let's type system
dot out dot print Allen and here we'll
say hello world and let's give a
semicolon at the end it was working on J
shell but when you work with Java files
because this is how you build a project
right Json is not to build projects it's
just for the experiment if you are
learning a language which is good but if
you want to make it work you can do if
you want to build a big application say
dot Java file and write your code there
so let's compile this code now how do we
compile okay so there are two steps you
have to follow first when you write a
code you have to compile the code and
then you can run the code so to compile
the code you can say Java C in the
terminal and let me just increase the
font a bit so you have to say Java C and
then you have to mention the file name
so first you have to be make sure that
you are in a correct folder which is
course you can see that this is a folder
we have and then you have to mention
Java C and then the file name the file
name in this case is hello.java click on
enter oh we got an error okay so it says
something is missing you know something
else was expected and you are giving
this is not working so this is not how
you write applications or code in Java
file we have to do something else but at
this point we have understood right how
do you work with JSL so you can if you
want to do something with JSL just write
a code it will work if you want to add
two numbers it will work you can't do
that here we have to do something extra
so let's solve this problem so we are
not able to run this code right this is
not working we want to get Hello World
on the screen it was working with J
shell because J shell says it's just a
password statement I will work but then
when you build an application when you
run the application how exactly it works
behind the scene once we understand that
we can write this code so in your
machine you will be having something
called j v m Now by default when you say
Java is platform independent is because
of jvm because in your machine you will
be having jvm irrespective of which OS
you use it can be Windows Linux based Os
or Mac or whatever famous OS we have it
will have jvm installed and of course if
you have jvm you can run Java
application and if you don't have jvm
you can't run job application okay so we
got jvm here right now what jvm says hey
I will work but then there's one
question when you say jvm will work but
jvm works on which environment so
underlying we have your OS so this is
your OSS and then your OS is working on
a hardware right so you'll be having a
hardware it can be a laptop it can be a
desktopic in your phone doesn't matter
you have a hardware on top of that we
have an OS on top of that we have
something called jvm now jvm says okay
my job is to execute a Java code okay so
whatever Java code you create JV will
execute that but then jvm will not
accept the code directly see what
happens is Java goes in multiple steps
in Java application when you as a
programmer so let's say you are a
programmer here and when you write a
code you will not directly run write a
code which will run on jvm okay and we
don't even do that right we don't even
write a code which actually works on the
hardware and we don't even know the code
which works directly on OS Java says if
you want to make it work you have to run
your code on jvm but then JV will not
understand what you are talking about
and one more one more thing we have
talked about right Java is platform
independent so what does platform
Independence means it simply means that
you can run your application on any
machine okay so when you write a Java
code it will run on any machine
irrespective of the hardware or the OS
but the only thing it requires is that
machine need to have jvm so irrespective
of which platform talking about if it
has jvm your application becomes
platform independent but jvm itself is
platform dependent okay so example you
can't run jvm on iOS so we can't say
Java is platform independent when jvm
itself is is dependent so yes your
application is independent jvm is not so
jvm need to be built for a particular OS
and let's say if it is Windows in my
it's so in my machine it is Mac but
let's say if it is Windows we have jvm
available on Windows so your jvm says
hey I will run your code but you have to
submit me not the Java code but
something called a byte code so you have
to convert your code into a unreadable
format for the normal human bin and this
is called a byte code
because jvm only understands byte code
but can you write byte code of course
not you only understands English type of
languages right so whatever we have
returned the code we have a
returnsystem.out.print it's English like
language right so what you create is a
Java code so this is your Java file or
Java code and then you have to convert
this Java code so this is Java code
which is mode of readable this is not
something which you can read so
basically you have to convert this into
a Java code or byte code so for that we
have something in between here which is
called a compiler now since this is a
Java compiler we can call it as Java C
which is Java compiler okay so basically
you will write this code so this code
will be getting compiled into a byte
code and that byte code goes on the jvm
it will run okay makes sense right so
that means when you write something it
will go into byte code and then byte
code will run on jvm now the only thing
is see your project can be a big project
right here I'm writing only one file it
can be 10 lines of code it can it can be
10 files it can be 100 files it can be
thousand files out of all these files
there will be only one file with jvm
Will execute okay JV will start with the
first file and then of course that file
will depend upon the files and it will
execute so jvm says you need to tell me
what that file is okay so if you even if
you have thousand files which you want
to run in your project you have to give
the first file so in this case what you
will do is you will specify hey that's
my first file so when you run the code
you will specify the first file and also
that file need to have something called
a main method okay so as I mentioned
before right we have print in the same
way we have main so your file the first
file need to have a main method so when
I say first file it is not like you have
to follow a sequence create this file
then that's that file out of all the
files in your project the execution will
start from the first file which you
specify okay and that file need to have
main not just main it is looking for a
specific signature okay so when is the
signature it means the entire method
signature the method name what are the
values you're passing and all the stuff
and of course all this term you will you
will get used to in some of these
sessions don't worry so first you have
to make sure that you provide a main and
Main has a particular signature again
what each word means that we'll see
later so the signature is this it is
public static void main so you have to
remember always pass this method I know
there are four words but then this is
the thing you have to remember and Main
will accept some arguments some
parameters so you have to pass string a
now again we'll discuss this what this
string is what is public static void
we'll discuss that in some time but main
is looking for the signature so your
code will not work without the signature
okay so remember this so that makes
sense so what are the steps you have to
follow so the first step is as a
programmer you will be creating a Java
file okay now once your Java is ready
you will put that into compiler then
compiler will compile it then that code
becomes a byte file a byte code
basically then you will take this byte
code you will run that on jvm now once
you once your jvm says okay I'm running
the code jvm will look for this vertical
syntax it should be there in your code
and then you will get the output right
simple stuff okay now there's a space in
between here if you can see this is a
space I have left left that space
intentionally because we'll add certain
things there so at this point just
remember there's a space here there's a
box remaining here we'll we'll add that
box in in some time now once we have
understood all those things it's time to
expand this code now if you remember we
have to write everything in a main right
so this section should be a part
of remember what jvm will ask you for JV
will ask you for main so we have to put
that into main so what your Syntax for
main it's very simple it is public
static void main we have seen that of
course this words will Define that words
in the upcoming session and once you
understand all these terms you are Java
programmer right and in this will say
string a and that's it this is a syntax
to follow now there is one more thing uh
in Java now Java is object oriented now
what is object oriented means we'll
discuss that later but in simple terms
object oriented means everything should
be an object and to create object we
need to class okay again we'll discuss
all those things in the upcoming session
but a class is missing here in fact if
you compile this code this is what your
Java say will tell you JavaScript says
hey where is your class your class is
missing okay let's do that so let's put
that a class here and we'll give a class
name at this point we'll keep the class
name and file them same and we'll say
Open Bracket and close and we'll give
our indentation so basically we have to
follow this thing always give a tab so
every time you open a curly bag give a
tab it looks good okay there's no
compulsion it looks good and we love to
build stuff which also runs and looks
good okay this looks good right ignore
this accent these suggestions uh these
are the exercises coming from your vs
code but you know that part in fact is
it because it's happening of this
extension let me just remove this so
let's not use that extension because it
will give you a suggestion it's good for
development but not for teaching purpose
so it adds extra text there okay cool so
this is how you write your code okay we
got a class a file name and then public
static void Main in bracket you have to
mention the parameters again we'll
discuss that later and the only thing
important statement here is
system.out.print Hello World okay now
let's see if this works let's create the
screen and compile you can see there is
no error but the moment I compiled if
you can see on the left hand side we got
this extra file we got hello.class now
this is your byte code remember we have
talked about a byte code here this is a
file which got created automatically so
when you create a Java file when you
send it for the compilation it will
create the byte code and the extension
for the byte code is Dot class file the
extension for Java code is dot Java file
and now it is compiled done right now
it's time to run your code so remember
when I mentioned to run you have to use
jvm and for that you have to use a
command which is Java and you have to
mention the class name not a file name
this time just a class name the class
name is hello and say enter you can say
we got hello world so yeah that's how it
that's how it works so simple stuff
that's why we can able to complete our
code and we are able to run this code
now if you have done till now give a
round of applause or a part on your back
because you deserve it okay so this
makes sense right so there's a gap here
right so let's remove this Gap so what
we have here so basically you know when
you when you run your code basically
think about you're cooking something in
a kitchen right so where do you cook of
course in a kitchen right why not in a
hall or in a bedroom it's because in the
kitchen to cook something you need extra
things right example if you make a
Biryani I don't know if you know the
recipe even I don't know the recipe but
if you make a Biryani you have to add
extra ingredients right now those things
are kept in the shelf so in the kitchen
you will not just have that resources
which are there in the platform but also
you'll be having extra stuff now the
same way if you want to run your Java
application you need extra libraries and
you also need a runtime now runtime is
something which where you can run things
right now you can run something in a jvm
so that is part of run but then what if
you need some extra libraries you have
to Unix you need a environment as well
so Java provides you one more thing so
we have one more layer here which is
above your OS which is called JRE so
when you want to learn something you use
JRE to run it now JRE stands for Java
runtime environment and what is your jvm
jvm stands for Java virtual machine okay
so basically we have two things we have
a jvm and we have a JRE now jvm is a
part of JRE now what else you'll be
having inside your jvm you will be
having some libraries so jvm with
libraries is a part of JRE so whenever
you've done something it runs inside the
JRE and jvm is actually responsible to
run it okay and by default when you when
you want to run your application on any
platform it need to have JRE which will
have jvm now not every machine will have
Java C Java C is only for development
purpose right so we can imagine this in
this section uh so basically we have an
outer box which is your jdk which is
used by developers inside which you will
be having something called JRE and in
this you'll be having jvm so as a
developer you'll be installing jdk jdk
will have JD Jr you will have jvm but to
run something on any other machine let's
say if you have met the application you
want to run this on your friends machine
your friends machine will only have JRE
and jvm jdk is not required and that's
why we say Java is Vora which is write
once and run anywhere right so you just
write on your machine you can run it on
any other machine provided you have jrd
and jvm installed so that's how your
Java behind the scene I hope it makes
sense now okay so we were able to run
this code and we understood something
what is happening behind the scene right
so basically we know now that as a
programmer as a as a Java developer you
write our Java code which will be having
dot Java extension and that gets
compiled by Java C and then when you
when you compile the code what you get
in output is a byte code which will be
having dot class file and then you can
run the dot class file in your JV I mean
basically it's a part of JRE which will
have jvm as well as a libraries lot of
classes and then everything is a part of
a JRE that JRE you will be installing on
OS right so basically you need to have a
hardware of course you need a machine to
run right that machine will be having an
OS and then OS will be having JRE which
is which will have jvm but as a
developer you will need one more tool
which is jdk now when you install a new
jdk you get the updated JRE and jvm with
it okay so the version of jdk which we
are using is is 17 which is LTS which is
long-term support and in every new
version you get some minor extra
features right so even if you are
watching this after 10 years or 80 years
or five years you will be having new
version of java of course next five
years you will get 10 new versions and
every new version will have minor
updates but the base Thing Remains same
right so whatever you're learning is
actually from java one itself the
system.pinterland is same in Java one so
don't worry about the new updates the
code concept will remain same okay cool
now once you have this thing what next
we can do now think about this world of
course first of all why we build
software we build software so that we
can solve a problem now what problem we
are trying to solve uh so basically we
are trying to solve the real world
problems uh with the help of virtual
world example you wanted to buy
something so you've got Amazon which
delivers everything at home so you got
Amazon is online service you want to to
book a cab you got Uber so for every
problem we have a solution in the
virtual world right so banking
everything is happening online now when
you say you are replacing the real world
with a virtual world solution so
basically we need to work with one thing
the most important thing now is actually
data so basically we want to work with
data so how will you work with data so
basically you need data as well as
processing on it so whatever whenever we
build a project or when you build
application what we are doing is we are
doing the processing on data now this
data can be coming from user or
something so maybe you will accept the
data from the user and then you will do
some work with it maybe you want to
store this data now where exactly do we
store data so we store data in something
called database so we have a database
here in which you will be storing your
data so whatever data you're getting
from the user or from after processing
so let's say we got a user here user
sends us data we will apply a processing
on that so we will do some work in
between and then then at the end we
might store data in database now this
database is actually a permanent storage
or a persistent storage which you say
now when you say it is permanent that
doesn't mean you can't change it of
course you can you can replace the
values as well but then the data stays
there okay so if you just store it and
if even if you shut down your machine
the data will be stored example when you
copy movies or games on your laptop it
stays there right it will get deleted
when you say delete but the data stays
there so this makes sense right but when
I say you will receive data from the
user and then you will be doing some
processing on that where you will store
the data for temporary purpose of course
database is there for permanent storage
but during processing you have to store
your data somewhere and that somewhere
is variable so this is where you store
your data now what is variable so
imagine variable as a box and in this
box you will store your data now what
data you want to store your data can be
numeric it can be text it can be image
whatever you want to store so you can
store that data in this variable now I'm
not talking specific to Java in general
user you want to store data you will
store that in a box and that box will
have a type to it it can be of type
numbers it can be of types text or image
or video so here we are trying to store
data right so let's I want to store the
number which is five so this box will
have a number five and it will also have
a name to it maybe I can give a name
let's say a number it doesn't matter
what name you give of course there are
some restrictions on names but num works
you can use any name which you like
maybe you can create one more box here
and you want to store the number itself
but let's say a decimal value something
like 6.5 you can do that okay and maybe
you can have a different value to a
different name to it maybe you can say
marks or grades or maybe you want to
have one more box where you want to
store your name so I can do that I can
store my name as Naveen and it will have
a variable name so maybe I can say this
is user so user is Naveen so basically
what you do is you create a box and
inside the inside the Box will be having
values now this box are actually called
variables so we can name this box as a
variable okay and so what we got till
now we got thought that a box will be
called a variable and you will be having
a name to it you will be having a value
so name and value will be there apart
from that you know Java is actually
called strongly typed language now what
it means is whatever variable you want
to create so if you want to store the
data of course Java says hey we'll
accept the data but tell tell me also
what kind of box you want a different
type of data will require different
blocks okay that makes sense so I will
say hey Java I want to store a number so
I want to create a box for me which will
accept numbers so we can say okay this
makes sense number will go there we can
also tweet this as a number but this is
a text right so in Java we call them as
a string right so text will be having a
string so this box type is string what
about this box of course we say this is
number this is also a number but in
number as well we have a category inside
it so one of the categories I will
mention is this we can if you want to
store numbers we can store that in
something called in now int means
integer okay so we can store data in the
integer format but we cannot store 6.5
in it because 6.5 is a real number so
int will accept numbers but white is
called int why not natural numbers or
whole numbers is because maybe you want
to store negative values as well so
remember your maths concept so we have
negative numbers to positive values so
everything will be considered as int so
we can store minus 5 plus 5 that's your
choice okay so this makes sense what I
will do now is if I go back to the code
of course we want to print hello world
but we have done that now I want to
store value so that I can do some
processing on it now what kind of person
think I want to do maybe I can I want to
add two numbers maybe two plus two or
five plus six simple stuff right but
before that we'll see how do we store
data even if you don't store data you
can just go inside this system.print
whatever option you want to perform you
want to say three plus five that will
work so you can just go back here and
say compile and run so remember this
thing every time you make a change just
make sure that you compile it first so
the first step is comparison and then
running and you can see we got the
output 8 just ignore this percentage
symbol as of now I'll show this one more
thing I wanted to mention whenever you
print something let's say I want to
print this number here as well I want to
perform different options so you can
write multiple statements for different
operation you want to perform so you can
say eight plus seven so we are doing
addition here and the addition here
let's clear the screen okay I have to
first compile okay that's what compile
run and you can see we got the value
now the only thing you can see is the
result are bit that together right we
want to give a space of maybe I can
train 15 on new line so what you can do
is instead of using print you can
actually use something called print Ln
now print Ln means print new line so it
will print and it will go on new lines
so we can do that here as well so just
say Ln Ln at the End Print Ln which is
print new line and now compile run and
you can see we got the value we got 5
and 15. so from now we'll not be using
print we'll be using Ln println okay so
again println means it will print it
will go on new line so we got print Ln
now what else we can do here so I don't
want to perform the operation here
remove that I want to store that value
first so how do we store it of course we
need box right so I can say num1 I can
as I mentioned I can use any variable
name so let's say num1 or to start with
let's say num just to keep it simple and
then we can give a value to it let's say
value is three so remember you have to
mention the variable name and then we
have to mention the value for it and at
the end of course you can put a
semicolon so we can see we got num equal
to 3 and we got semicolon so in Java
after every statement you have to give a
semicolon you might be thinking hey why
don't we have a semicolon here it's
because that is a block so we don't put
a semicolon out at the end of a block
the reason is it signifies that's the
end here if you don't mention semicolon
how do we Define that that's the angle
so it's good to put semicolon at the end
and anyway Java will give you either if
you don't do that the next thing you
have to do here is we have to also
mention the type what type of num is
this so we can say int now we have to
say first you have to specify the type
and then you mention the variable name
maybe if you have learned some other
languages where you put the type
afterwards in Java we first put the
value or put the type and then we put
the name then we Ascend the value now
this equal to here is called assignment
operator because you are assigning a
value so what it will do is it will take
the value from the right hand side it
will assign the budget to the left hand
side okay remember this equal to will
take the value from the right hand side
it will assign the value the left hand
side okay so we got a variable which is
of type int okay so this is num which is
a variable and then we can print it now
let's only print the value that's it
nothing much I will say save now once
you click on save you have to compile
the code
and run the code and you can see we got
three Okay cool so now can I create more
variables we can actually so let me just
rename the value variable from num to
num1 and here as well I will print num1
okay and then I will create one more
variable which is num2 is equal to so
every time you want to get a variable
just mention the type which is int or
whatever type of variable you're
creating at this point we are working
with numbers so we'll say end num2 equal
to we're going to assign the value which
is 5 so we got 3 and 5 here what you can
do is you can actually perform the
operation here itself so against the
num1 plus num2 that works so instead of
adding values we can also add the
variables okay so now we are what we're
doing is we are saying num1 plus num2
and the addition will be getting printed
let's try so I can just go back here and
say compile run and you can see we got
eight you know what instead of adding it
inside this it's not a good practice
what you can do is we can create another
variable called result and that's right
variables are free to use of course
behind this engine is consuming a lot of
memory
but it's working right it's free as of
now but later on we'll focus on how can
you make your code more efficient so
that it will use less space right at
this point it works so we can say now
one plus so whatever option you want to
perform you can do that here and instead
of printing and this is doing addition
here we can simply print result so what
you're doing now is you're adding the
value and then you are storing that in a
result and then you are printing it it
should work let's try compile run and
you can see we got eight so this is
working so that's how you can you can
create variables so remember this thing
every time you want to create a variable
you have to you first need a name for it
at this point is num1 you have to also
mention the type of it at this point
this is int and you have to assign the
value for it in the upcoming videos
we'll talk about how can you create a
variable which will be having a name
with a different type and different
value so now we know what variables are
and how do we create them so basically
in the last video we have talked about
how to create a variable with the help
of the data type and the value as well
now what are the other options we have
so we have worked with eight right do we
have other options so basically we have
multiple data types to store your data
so let's talk about the first thing
which is uh data type in fact there are
two categories of data type which we can
normally work with one is called
primitive and the other one will be will
keep it question mark okay at this point
we are not just discussing about the
second one the first one is primitive so
basically in Java we have lot of inbuilt
data types available which you can use
and they are primitive now primitive
simply means it is simple basic to use
to work with so what about data you
normally have normally we work with
numbers we work with Point values we
work with characters we work with true
or false now for that we have this that
category so we can divide primitive into
four categories here uh the first way
one the first one is of type integers uh
the second one we have is float floating
point value basically so we can say
float and the third one is characters
and the fourth one is your bullion of
course when you divide this we have more
categories to it but in general we have
four we have integer float character and
Boolean now when you say you want to
store a range a negative range to
positive range numbers normal numbers or
natural numbers you can say in fact we
can we can call them as integer itself
because we are starting with a negative
value so that goes into integer whenever
you have Point values which that goes
into float value whenever you go with
characters like a b or any Regional
characters you have all across the world
that goes into character and then when
it comes to true and false we go with
Boolean now inside integer itself we
have multiple subtypes to it uh we have
a concept of byte we have short we have
int and we have long uh for float we
have another option which is of double
and of course we have float and then
carries characters are characters so in
characters we can have different type of
characters in Boolean uh the only values
we can have is true and false okay uh so
example if I go back to my code and if I
want to create a different video table
this time let's say float so I can just
come back here I can remove this section
and here I can say this we are creating
a float value now how do we get a float
value base so we can simply say float
and then we can have a value let's say
seven or we would name to it right so
name we can have is marks of course we
don't put in marks but let's go with
marks and then we can go with a value
now floating Point values would be
having a DOT right so we can say 6.5
something like this uh some float marks
equal to 6.5 that makes sense right okay
cool in the same way we have also
mentioned we have subtypes to integer we
can have a byte format but why do we
need all these extra formats for that
let's understand uh some basic concept
now basically when you talk about
integers itself so if you talk about
integer we have some sections to it so
integer will have different part so
interesting will have different sizes
example if you want to store a normal
number so in general we always go with
int and int has its own value okay so
when you talk about in the size of int
is is four bytes so we can say 32 bits
and then it has a range to it and you
can find the range on the screen uh we
also have a format which is let's say if
you want to store a bigger value a very
big value so in this case I'm I mean of
course the value goes beyond that range
we have to go for the long format now
long supports eight bytes now of course
when you have more budget it will occupy
more values and it will have a range so
of course you can find the range on the
screen now what if you want to store a
smaller number so of course int provides
you that range but then what if you want
to save memory you don't want to go for
end range in that case we can have a
short value now short is only two bytes
so if you want to have a limited range
you can find the range on the screen and
then we have the next range which is of
byte now byte is only one byte okay so
eight bits and whatever you want to
store you can store in that of course it
has its own range now how do we
calculate this range so we do with the
help of it goes from negative values
right so it is minus two raised to 8 2
plus 2 raised to eight minus one okay so
which is 2 s to 8 is what it is okay
starting with negative value right so
just two is to 7 and 2 is to 7 and the
range so how do we calculate version 7
is 128 so it starts from minus 128 to
plus 127 so 128 minus 1 127 that's how
you can calculate the range for all the
other numbers and you can of course you
have seen that on the screen so this is
how we can use integer so which one to
use so if you want to get a variable
which is a which will have a value let's
say five or six or maximum 127 you can
go for byte now how do you get that
variable it's very simple you use a type
which is byte you specify a variable
name let's say num and you assign a
value which is eight or any other value
which you want of course that should be
in a Range and that's how you can store
it now what if you want to have a float
value now float actually gives you two
different values or two different types
now it depends upon which programming
language you have worked with before
example if you have ever worked with CVA
by default we have a value which is
float so by default we have float there
now float only takes four bytes and it
has its own values you can store and
then we also have option of double which
takes eight bytes now what you think
which will be default value think about
it will it be float or double by default
in Java so default is actually double
not float okay now why double is because
see float are good when you have limited
values when you have limited Precision
because after your point value example
if you have value which is
126.5678 or whatever values you have so
float will have a limited Precision set
here but on the other hand double will
have a longer one right so double can
have more values so whenever you perform
scientific calculations or any kind of
calculation if you wanted to make it
fast and it should support maximum
Precision you can use double there right
and by default Java supports double so
if you want to create a variable which
is with double so you can simply say
double and you can create a variable
name num is equal to you can assign a
value which is 5.6 so whatever value you
want to assign but how about float now
if you try that with float it will it
may not work example if you say float
and if you say a variable name which is
num and equal to so when you try to
assign 5.6 it will give you error it's
because by default the moment you say
Point values it will be considered as as
double and if you want to say hey I
don't want to work with double I want to
work with float so explicitly you have
to mention hey okay this is actually
double value so you can this is actually
a float value so you can put a f there
right so 5.6 F that's how you define
it's a float value for double you don't
have to mention that now how about
character so when you when you work with
character and in other languages
character will have a less bits but in
Java it goes for two bytes so so in
other languages like C you have only one
byte it's because it normally occupies
the integer range it normally occupies
the character range ASCII values but
then in Java we thought hey can we just
have all the characters in the world not
just English all the languages so Java
actually follows something called
Unicode not ASCII by default it will
support Unicode and it has two bytes
which is 16 bits so it has a bigger
range right so this is a range it
normally works with so of course you can
work with any type of values you have
and any type of characters basically you
have and if you want to define a
character variable it's very simple you
say Cad and then you specify the
variable name let's say character or c
equal to whatever character you want to
assign let's say I want to assign a
character which is K now in this K in
this case if you want to work with a
character can we use double Quotes no
double quotes is for string right for
character we have to use single quote
and you have to put your character to
single quote and remember it will only
accept a single character and next we
have of type Boolean so if you want to
work with Boolean Napoleon will only
accept true or false okay no other
there's no subtypes here only true or
false now one thing you have to remember
now in other languages it may represent
it with the help of one and zero in Java
we don't do that so in Java it does not
it doesn't work with zero and one it is
true and false this Knight like true is
one and false is zero it's only true and
false it is normally used for conditions
if you want to check for the condition
based on that you will do something
that's what we can use two and false I
mean think about computers when you say
computer can think it's because of this
true or false okay and how do we Define
a Boolean variable so it's very simple
you use a keyword called Bull and then
you mention a variable name let's say B
is equal to you either assign true or
false okay you don't have to put a semi
a single quota double quote because they
are itself keywords so these are the
options we have now if you want to see
this in a code it's very simple you can
just go back here and say okay byte is
done let's create some variables with
different type so ain't we have already
seen so it's a number one this is how
you assign integer value what if you
want to go with a byte so you can say
byte B I will say b y equal to now can I
assign a value which is 129 you can say
it will give you if I do that if I go
back to my compiler compile you can see
it will give you error it says possible
lossy conversion from into byte so this
is int which is 129 it will if you try
to save that in a byte it will not work
but what if you say 127 that's the last
value you can store compile okay this is
a problem with result let me just remove
this section and compile no issue okay
so this is how you save byte value what
if you want to store shots you can say
short sh equal to
and you can assign value which is let's
say five five eight any even number
doesn't matter and then what if you want
to work with long so long L is equal to
now when you work with long remember
this thing after every number for long
you have to put a l at the end to
specify that's a long number the thing
we have done with float we have to put F
in the same way long needs l
and what if you can do here with float
so you can say float f is equal to
5.8 okay let's try with 5.8 and let's
see what happens if you try to compile
this compile okay you can see it is
giving you it says again possible logic
conversion from double to float because
by default 5.8 is double if you want to
mention hey that's not double that's
float you can put a f at the end that
should work you can work with double as
well Double D is equal to 5.8 same value
but this time it is double and then what
else we can work with we can work with
character as well so we can say care C
is equal to in single code you can
mention the character k then we can go
for Boolean which is Boolean in this
case and you can say B is equal to True
simple stuff right uh let's try to
compile this of course we are not
printing anything so we don't expect
anything on the console compile or
there's an error it says cannot find
symbol bull okay my bad it is Boolean
the only problem is when you work with
multiple language at the same time you
get confused somewhere so that that's
Boolean notable so in the notes as well
I need to change it so I will say this
is Boolean
cool and now let's compile this once
again compile okay there's no problem
and let's run this of course it will run
but then you will not see any output
right no output because we're not
printing anything so yeah that's about
this we have different type of
data types we can work with and all
these are inbuilt apart from this we
also we also have some more data types
which we'll see later they are not type
of primitive but this is primitive data
types and this is working okay awesome
so now we know what what variables are
what data types are what a size or range
of each data type here and you don't
have to buy hard them you will get used
to it the more practice you do with this
variables you will get used to when to
use what but what if I remove that
single code there let's try compile and
you can see we got another we can't even
put double quotes there it will give you
as well and you can see you can't even
put double code so you have to put
single code because that's how that's
what character represents and the
character can be numbered as well so you
can put a character here which is eight
which is the character itself right
digital also character no other
okay so when you talk about data types
and then values what kind of values we
can have so example if you talk about
this 9 or this eight these things are
actually called laterals
because they're literally the values
right so what we can do is we can play
with some literals here let's work with
integers first and we'll come back to
this so we are basically working with
literals now okay now what kind of
relatives we can have for example we can
have direct values we have nine here and
we can have any big value provided that
goes into the range so whatever range we
have it is a part of the range it will
work so we have all these are decimal
values right so it will have a base 10
what if you want to work with base two
something like a binary format can we do
this let's try it so I will say 0b 1 0
1. so basically if you want to put a
binary number like 101 which is five so
you can put B and then you can put a
zero let me just drive this works I will
say system dot dot println and then let
me print num1 let's see if this works
put your semicolon at the end
compile there is no issue so let's run
this code and let's see what's the
output and you can see we got five so
yeah that's the binary format Works what
if you want to work with hexadecimal
numbers in this case you can use x here
and let's put a number seven e so e also
supported right so let me just try
compile run and you can see we've got
126 I don't know if that's the correct
answer but you can verify there's one
more thing which will introduce later in
Java which is what if you have let's say
this number and trust me I always get
confused with number of zeros in any
amount even if I mention a password or a
pin or account number and whenever you
have multiple zeros I always get
confused so how do you count to the
number of zeros here of course you can
do it one by one but in Java we got this
feature where you can put a underscore
between numbers if you want to
differentiate them it was easy to count
right so you can see we are getting
zeros and then we got underscore even
this works let's try it out compiled one
and you can see we got the output of
course in the output it will give you a
normal number but as a programmer it
helps you for the number of zeros you
are entering that so these are basically
individuals right let's try with float
this time so let's say this float and we
are saying num1 and then I want to
assign a very different value can I
assign let's not let's go with double
just so that I can avoid that F at the
end and here I want to assign let's say
56. so basically when you try to assign
a integer value to float it will work or
double it will work because integer will
get converted into double automatically
when you save it okay uh okay that makes
sense can I have different value let's
say I want to store a very big number so
I can actually use Epsilon e in between
I can say 10 e 12 e raised to 10 and
let's see if that works compile run and
you can see we got the value as well
here and it will adjust automatically
based on its own implementation so it is
assigning 1 0 here so there's basically
12 into 10 raised to 10 or 12 into 10
into 10 to 10 and then it will I just
it's according to its own way and we
have one we have already discussed about
the Boolean it is only true and false
there is no one and zero there uh don't
try to assign
one it will give you error let's try
compile okay you can see we got there it
says int cannot be converted to Boolean
remove this okay how about character
let's try uh so when I say character
let's just see and I want to assign a
character here which is uh say in single
code let's say a now when you try to
print the character uh this will work
compile and run you can see we got a now
basically character can be also treated
as integer that's right we can actually
perform operations I can say C is equal
to C plus one so what I'm doing is I'm
incrementing C I'm enhancing the value
of it if it is a normal value value it's
a 5 it will become six okay what if you
want to do an increment of course we'll
discuss this later what increment means
but you can say plus plus to increment
the value and if you try that with
character compile it you can see that it
is getting compiled and if I try to run
this code we got a or because we are
printing it there my bad I will just
have to put that here so first we have
to increment the value then we can print
it so C plus plus implements changing
the value okay it's not a language I'm
talking about the operation on a c
variable and you can see we got B so
when you increment the value of a it
becomes C it becomes B cool so basically
all these things are called literals in
fact there's a concept of string
literals as well where you example when
you talked about hello world that's a
string that's string literal in this
video we'll talk about type conversion
and type casting so in the previous
video we have talked about variables how
to create a variable and then one thing
is for sure in fact two things every
variable needs a name so we have talked
about it and every variable needs a type
as well so if you want to get a variable
for numbers you will say ain't float
double or long in fact we have sub tabs
as as well for INT and then if you want
to store a character we can use care if
you want to store a Boolean value we
have Boolean option and then we also
have a string which we'll talk about
that later at this point we have a lot
of different types now there is one
confusion what if you want to change the
type of a variable can we really do that
so so unfortunately we can't we can't
change the type of a variable but then
can you assign a value to other type
example let's say we have a variable
which is of type byte so I'm using a
byte variable which is B and it will
have a value now of course we have
talked about the range of byte as well
you can have maximum 127 plus I mean
plus 2 127 this is the max value you can
accommodate here but can you assign a
integer value that's a question so what
if you have a variable of type int a and
the value of a is 256. now what will
happen if you try to assign this a value
which is 256 into B something like this
what if I say B is equal to a so what
I'm doing now is I'm assigning a value
of integer to byte now unfortunately
this will not work but what will work
the reverse will work what if you have a
variable which is a and then you are
trying to assign a value which is B this
will work so what happens is the type of
a is integer right it has a bigger range
and byte has a small range so the
compiler says hey you're trying to
assign a integer value to byte and at
this point you will lose you might lose
some data so basically we are trying to
convert it and it is narrowing it right
so we are narrowing the size of it on
the other hand if you talk about this
operation here we are widening it
because this the range of byte is small
and integer is a bigger one so of course
you can put a small items in a bigger
box but if you put a bigger item in a
small box it will not work right okay
cool so that makes sense right but then
what if you really want to do it you
want to convert a integer value into
byte see at this point if the value of a
is not 256 what if the value of a is
let's say 12. now the value of a is 12
which can be accommodated in b as well
so at this point even your compiler will
say hey I don't know what your value of
a is but I will not allow you to store
the value of a in B because a is integer
and B is byte so in this case you can
say hey compiler give me one second here
what you can do is you can say B is
equal to you can convert a you can do a
conversion by saying you can give a
bracket and you can mention the type in
which type you want to convert you can
say byte and you can mention the
variable name a so what you're doing is
you're converting integer value into the
byte format okay now this constant is
called casting so basically this is
actually a conversion but explicitly
you're doing it so whenever you do
explicit conversion it is called casting
so when I say explicit there should be
implicit as well right and that is
correct we have some conversions which
are implicit example if you talk about
this particular operation here this is a
implicit conversion basically you are
trying to store a byte value into a
integer variable so it becomes integer
when you assign it right so this is a
conversion okay so when you do it
explicitly that is casting when you're
disopening if it is happening
automatically that is conversion now
this makes sense right now is it means
you can do it with anything not exactly
there are certain types example you
can't store a character value into a
Boolean value okay because Boolean only
supposed to end false and character
supports all the characters so you can't
do those conversions but anything in the
range of integer float double actually
works example uh we have talked about
integer and byte if it is long as well
that completely works now what if you
have a scenario where you want to store
maybe of type a float value now let's
say you have an integer variable here
which is int let's say x is equal to and
you're trying to assign a float value
now float value is let's say 5.6 of
course I can create a float variable I
can assign this value to that or maybe
this is double because we don't have F
so let's say this this is double and
then you're trying to assign that to
integer now what will happen is in this
case if even this will not work so what
you have to do is you have to apply you
have to convert it so what I will do now
is let me just create a float variable
here so I will say float f is equal to
5.6 and remember you have to put F at
the end now if you try to put f it will
not work so what you will do is you have
to explicitly convert this value into
integer so what you're doing is you're
assigning a float value to an integer so
you're converting it now what you will
lose here so at this point you will lose
your point values so whatever value you
have in after that point you will lose
an example the value of five point which
is 5.6 so here when you convert that it
becomes 5 so in the X the value you will
be getting is only five cool uh so it
makes sense right so for float it will
cut the value but coming back to byte
now what will happen when you talk about
byte here what do you think we don't
have Point values so if you have a
bigger number example let's say this is
not one this is not 12 let's say we have
a bigger number here and the bigger
number is let's say
257. now what will happen when you
assign 257 because the range ends at 127
you can't go beyond that right so in
this case it will use a concept of
modulus okay or modular operator so what
modular will do is it will divide this
number so whenever I try to assign a
integer value to byte which which we are
doing here so when you are trying to
assign a integer value to a byte it will
convert that into modulo which is it
will divide the number a which is 257
and it will find the percentage okay so
257 percentage which is a modular symbol
and it will divide it with a range okay
which is 2 256. because a complete range
of byte is 256 right from minus 128 to
plus 127 and then the remainder you will
get here is one cool so the answer here
when you try to do it with the 257 it
will be one I will show you that in the
code so coming back to the code let's
try all this operation which we talked
about so what we'll do is we'll start
with a integer value we can say or maybe
we can start with byte so we can say
byte B is equal to and maximum you can
have is 127 let's take that value and
let's try to print it here so we can say
system Dot dot out Dot println and here
let's print the value of B so when you
save that and when you go back here when
you try to run this so we say Java C and
Hello dot Java comparison done let's run
this code I can say Java space I have to
run with the class file which is hello
and you can see we got 127. now what
will happen if you try to do that with
257 it will not work first of all it
will say either you can see we got data
it says incompatible types because it is
integer type now 257 okay so you can say
127 here now next what I'm going to do
is I want to create a integer variable
here which is int int n is equal to and
I can assign a value maybe let's say a
because we have used that so we'll say a
and then the value we are going to
assign is of B so can you assign a byte
value to integer because this is this is
where you're doing converting and if you
try to print the value of a let's try
that in fact there's one more thing
which is which came recently in Java so
basically you know we always do two
steps right first you compile the code
and then you run the code right so you
compile that with the help of java C and
when you compile it you see you say
hello.java and when you run it you say
simply say Java and hello you have to do
two steps right so when you're into
learning phase why to do two steps you
can actually do a single step again not
recommend it for a big project or not
even for a small project don't you don't
even try that in your company for
learning purpose we are doing it so
basically we got a shortcut we can say
Java space Hello dot Java directly maybe
it is getting influenced by the other
languages where you simply mention the
command and a file name no need to
mention compile and run Subway step
let's try this and you can say it works
so you can see we got 127 it is
perfectly working and just to show you
that things are happening behind the
scene uh the value is getting changed
you can see we got 125. so from now from
whenever you have single file will use
this but remember this is just a
shortcut ultimately behind the scene we
need to do this okay I mean when you
build a project first you have to
compile the code then run on the code
this is a shortcut and one more thing
this will work only in the recent
version of java I guess from java 14. if
you have an older version of java this
might not work so if it's not working in
your machine that means you have an
older version upgrade your jdk version
Okay cool so now what I will do here is
we can assign the value right but what
if you have a integer value let's say 8K
and now you are trying to assign or
maybe let's let's get a byte value byte
K is equal to a and let's comment this
section instead of saying B I want to
assign a value which is 257. now even if
you have a smaller value let's say 12
even this will not work because
ultimately the value the I mean the type
of a is integer right you can't assign a
integer to a byte format and if you run
this code you can say it will give you
error it will say incompatible types so
we got one way which is you can just
cast it with byte so we are doing a
typecasting here so when you run this
code now it will work you can say we got
12. now we got 12 because it is a in a
Range of bite what happens when you have
a bigger value which is 257 now this is
out of range right so you can come back
here run and you can see we got one as I
mentioned before it will perform a
modulus operation which is actually
finding the remainder so it will divide
this number by the byte range which is
256 it will find the remainder which is
one I hope this makes sense right so we
were able to do the byte conversion in
conversion this is working let's try
with float now so let's say we have a
float value which is f and the value of
float is 5.6 F at the end because when
you look at a float variable you have to
put at F at the end and then we can
create a integer value we can say int
let's say this time we'll go for T
doesn't matter what variable name you
use and then if you try to put F there
and if you try to print the value of T
let's see what happens you can see we
got error again the same thing it is it
says there might be loss of the value
from this conversion but then I want to
do it I want to convert that so we can
put a casting again and we can say float
here and if you try to run this code so
you're trying to convert that into
integer right what's wrong with me and
let's try now and you can see we got
five so we lost that point six there now
this concept of casting is actually very
important when you start working on the
oops concept object and the further
concept this casting will be required
there as well at this point we are doing
casting on primitive values but later on
we'll also work with objects
okay now we have talked about casting so
what is conversion so conversion is
automatic
or we can say conversion is automatic
conversion and casting is explicit
conversion so when you specify something
it is explicit cool now there's one more
concept which is type promotion so what
are what what do you mean by type
promotion so let's say we have a byte
value and the value for byte let's say b
or maybe let's say a and the value is 10
here okay and then we got a byte which
is B is equal to 20. and then when you
perform the operation maybe maybe this
should be 129 let's let's say this is
30. now when you perform an operation on
this let's say a into B now whenever you
do a into B it is what 300 right so when
you say 300 here it is going out of byte
now can you save that into integer can I
say int result
is equal to a into B now what is
happening here you're performing an
operation on buy so when you
know Java says hey we will promote you
so this value will be promoted into a
integer value okay and you can store
that into integer so this is called type
promotions let's run this and you can
see we got an error because we are
printing T here let's print the result
and run and you can see we got 300 so I
hope it makes sense what is Type
conversion and casting in this video
let's talk about operators that's right
you can perform operations on different
values in fact we have done that before
but let's expand the examples and more
operators so basically we can add two
numbers we can subtract two numbers we
can divide two numbers we can do we can
multiply two numbers and also we can
perform an operation so that you will
get a remainder of an operation okay so
when you divide a number and if you only
want a remainder we can do that as well
so let me show you those things with a
code here so what I will do now is first
of all let's create two variables and of
course we can name any variable name but
let's go with integer num1 and the value
it will have let's say seven and then
let's have one more variable here which
is let's say five uh num2 is 5 and then
I can perform some operation and I can
save that operation in a result so let's
say if you want to add two numbers we
can do that we can save the output in
result and then to perform the operation
we can use a plus operator that's right
we can actually use a plus operator to
add two numbers and then once you have
done that we can simply come back here
we can say system dot out Dot println
and here we can print the result and
just to see if it is working and as we
discussed before this is not a good way
of running a code you have to first
compile the code then run but we got a
shortcut I can simply use Java space
file name which with DOT Java say enter
and we got 12. so when you say 7 plus 5
we got 12. cool now what I will do is uh
so we can add two numbers what about
subtraction let's try that so I will say
minus symbol and run you can say we got
two so just talking so you can add two
numbers we can subtract two numbers how
about multiplication we can do that so
we can say star num1 into num2 come back
here one you can see we got 35. so 7
into 5 is 35 that work that is working
how about division uh let's try that so
the moment I said division we have to
use a slash okay so we don't have a
division in fact that's how we do right
we say underscore or something obviously
slash so yeah we got uh Slash let's try
and you can see we got one that's right
one is a question here right so when you
divide seven by five you get two things
one is a question which is one and then
you will also get a remainder now in
this case when you use slash you will
only get a quotient not a reminder
so how will you get a remainder in that
case you have to use a modulus operator
so we can use when you say percentage
symbol like this it is a modulus
operator that what it will give you is
only a remainder okay so if I run this
code you can see we got two to the
remainder here right now we can use any
complex numbers as well whatever number
you want to perform with and I would
suggest you to try certain examples so
that you will get the get used to these
operations now all this operation
actually makes sense right these are
very simple stuff to understand can we
use some other operators as well let's
try what I will do now is let me just
remove this result for time bin or maybe
I can just comment this part I also
don't need this num2 let me only focus
on the first variable which is num1 now
let's say I want to uh add this number
one by two okay so basically the value
of number is seven I want to increment
the value by 2. so what we can do is we
can say num1 is equal to so basically we
have to use num1 which is number one in
this case and we'll add a value to it
which is two and then whatever new value
you will generate after this will be
assigned to num1 okay that looks cool
right uh let's try this I will say num1
print num1 and let's run this code you
can see we got nine so this is working
so seven became nine so just walking
right now when you know that you are
adding the number by itself okay uh what
you can do is you can just use a
shortcut
now what that shortcut says is let me
just comment this section here and let's
write it fresh here so I will say now
one
see you want to increment the value of
num one by two right you want to add
Itself by two so you can say I want to
add myself
but how much value so I have to say
equal to 2. so what we are saying is we
want to increment num1 by 2. even this
should work let's try or we got an error
because I forgot the semicolon
and let me just clear this run and you
can see we got nine so this is working
cool now it's not just tradition we can
do that for any other operation maybe
you want to subtract a number by two so
we can say subtract equal to two so it
will reduce the value by two you can see
God we got five we can multiply with
some other number maybe I want to
multiply the same number with another
number and assign it so we got 56 7 into
8 to 56 we can divide as well and so you
can use slash and all the operators
which you have awesome so this is
shorthand now going back to the addition
operator and then let's say if you want
to add it by two we can simply mention
the value 2 right we can also add it by
one so in this case if you say add it by
1 the value of num1 is 7 and then you
are adding it by one you can see we got
eight now in fact there's a shortcut for
this as well what you can do is instead
of using num plus equal to 1
you can also say num1 plus plus even
this is possible let's remove the space
in between so even this is possible you
can say num1 plus plus which is
incrementing so what we are doing here
is something called increment and if
you're on this chord you can say we got
eight so this operation let me just make
it one so all these operations are
similar okay so why I'm saying similar
why not same I will discuss that in some
time but this is similar
and maybe if you have done that before
as well when we talked about characters
you know we remember C plus plus we've
done that so yeah we are incrementing it
as well now not just incrementing we can
do decrement as well so instead of
saying num plus plus we can also say num
minus minus so what we are doing now is
decrement so when you say plus plus that
is increment let me comment this part
and here I will say num minus minus now
why you have to comment this but I want
to run this so we can say num minus
minus let's run this code if say this
works and you can see we got six so
that's how you can perform this addition
subtraction multiplication division and
increment decrement in fact we have also
talked about modulus which is for
finding the remainder okay now that was
about increment decrement right we have
talked about that now instead of using
plus plus we can actually use something
called let me just write it in comment
so instead of saying num1 plus plus we
can also say plus plus num1 you know
just to simplify this example instead of
saying num1 everywhere let's say num so
that maybe you will not get you will get
confused by that one extra symbol there
which is one uh just ignore all this
operation just focus on this part which
is numb and numb also remove this also
remove this let's see if this is working
okay this is working so basically we can
also say instead of saying num plus plus
we can also say plus plus num now what's
the difference between these two even
this also work let me just try that and
show you you can see we got eight we are
incrementing the value even this will
give you eight but what's the difference
what's the difference between writing
this afterwards and writing before the
variable so basically we have a
different names to it so whenever you
perform operation after the variable it
is for increment or decrement so when
you do it post we say it is post
increment and when you do pre before the
variable it is called pre-increment okay
so when we are doing it afterwards we
say post increment when we say before it
is doing pre increment now you might be
thinking hey ultimately the value is
same right so even if you pull even if
you do this or this both will increment
the value then why we have to defend
Syntax for it why not just simply one
the answer is it behaves differently
when you try to assign a value when you
try to fetch the value let me repeat
these two operations will behave
differently when you try to fetch the
value okay let me tell you what I'm
talking about let me show you here let's
come back here and let's say I have a
different variable which is ain't and
then I'm storing that in result and what
I'm storing is num or maybe I will say
plus plus num okay now think about this
and maybe you can pause the video or
whatever you want to do just think about
the what will be the value of result
okay I will say result here to print and
maybe you have done your thinking let's
run this and you can see we got eight so
what is happening here is the initial
value of num is 7 and then you are
saying plus plus num that means you are
incrementing it that incremented value
will be assigned to result okay and then
you got result which is eight okay so
initially I've also mentioned that this
two will be incrementing so we can also
say num plus plus even this should be
doing the same thing right let's try oh
there's a Twist here so plus plus num
and num plus plus are not same I mean it
works same with their individual
statement but when you try to fetch the
value from them when they are performing
the operation they behave differently so
let's understand what is called
pre-increment and what is called post
increment so whenever we use assignment
operator with this operation what it
will do is it will check hey we have an
option which is num plus plus but that's
a post increment so first it will fetch
the value of num let me repeat it will
first fetch the value and then increment
in fact it looks like one statement but
we have two statements here right in
fact we have this statement here num one
equal to num plus one so what it will do
is it will first fetch the value of num
which is 7 in this case and then it will
increment the value of num and it will
make it eight okay but then what is
assigned result is 7 itself and then you
are printing that seven here okay but
what will happen when you say let me
just write it here so we'll say end
result is equal to plus plus num in this
case what will happen is it will first
increment and then fetch the value okay
so it will first increment itself and
then it will fetch the value and that is
what is going to result I hope this
makes sense right so this is how your
code works when you say S Plus num and
num plus plus in fact we'll do some more
operations with this once we get started
and it will make much more sense later
so in the operations we have talked
about other thematic operators till this
point so whatever operation we have done
it is for the arithmetic purpose right
addition suppression multiplication
division but what if you want to compare
two values what if you want to have
compound conditions so we are talking
about operators right so we have talked
about arithmetic operators where we can
do calculations we can add two numbers
we can subtract two numbers in fact we
have also seen how do we increment a
value and decrement right now it's time
to enhance and go towards something
called relational operators in Real
World what we do is we basically have uh
we compare We compare things right so it
can be comparing two values and if you
can check with the help of less than uh
you can check with the help of greater
than you can also compare with two
values right if they are equal or not so
we use something called equal to there
right uh what if you want to negate
something what if you want to find a
negative eight example uh if you have a
True Value maybe you want to make it
false so in that case we also have to
move from True to false right so
basically we want to implement this with
the help of operators in programming
language now specific to Java if you
talk about we have different operators
we can use less than to compare with the
help of less than or less than uh the
first value should be less than second
value if that is true of course you will
get True Value we can also check for
greater than we can also check for equal
to now the only difference is when you
talk about equal to in programming
specifically for Java equal to means
assignment operator example let's say if
you have a value which is 5 and you want
to assign that to a particular variable
let's say x so you say x equal to 5. so
this equal to symbol here actually
becomes your assignment operator but
what we want here is we want to compare
two values right so that's why we use
double equal to so in programming in
Java we use double equal to come to
compare two values what if you want to
check if two values are not equal in
that case we can say
exclamation and equal to okay that's
that's what you say it is not equal to
so this is comparing for equal and this
is comparing for not equal and this is
of course less than this is greater than
and you can also combine example if you
remember in mathematics we use the
symbol Which is less than equal to in
the same way of course we don't have
this key on the keyboard so we have to
use less than uh
so we have to use less than equal to for
this particular combination uh we can
also say greater than equal to right so
we can use all this combination which
comes up as a part of a relational
operator now basically when you compare
this to what your example let's say if I
want to compare if 7 is less than 5 so
this will return u a value which is true
or false so it will be either true or
false of course we got a static value
here which is seven and five so the
output for this will be of course false
but if you say 5 is less than 6 yes
that's true so that's how you define uh
that's how you compare two values and
that's how you get the output the point
to remember here is the output which
you're going to receive is a Boolean
value okay now how do we Implement that
in a code so let's go for that so let's
say uh we have this our we have our code
here and in this what I'm going to do is
I have two values let's say integer I
can say x equal to 6 and then I got Y is
equal to 5 and now I want to compare
these two values the way you can do that
is of course when you compare these two
values you will get a Boolean value so I
can say Boolean uh against the result is
equal to now how do you store a value
and how do you compare so first of all
storing is easy you can just assign the
value but how will you compare in that
case you can say x is less than y and of
course that's available on keyboard so
you can directly use it
and what I want to do is I just want to
print uh the output here
so I can say system Dot
out dot println just for printing stuff
and then I can just say result now the
moment you say result it will print the
output and of course you have to compile
this code and the way you can do that is
by saying Java C
demo.java enter okay there's no issue
with the compiling because the syntax
looks good and now I will just run this
I will say Java demo enter and you can
you can see we got false now why we got
false is because the value for x is 6
and the value for y is 5. so the first
value is lessons is not less than second
value and that's why we got false
greater than simple here it actually
makes sense because that's a
oh remember every time you make a change
first you have to compile the code and
then you can run the code and you can
see we got through this time so
basically that's how you can compare two
values and you can print it but what if
these two values are equal so let's say
we got 6 and 6 and now if we try to run
this code of course compile and run we
you can see we got false
okay but then they are equal right so
maybe I want to check if two values I
mean if the first value should be either
greater or it should be equal
so we can put that uh equal to symbol
here as already discussed and now I can
just compile and run and you can say we
got true so this is working
we can also check for less than even
that works because it's equal right and
anyway we have equal so it should work
so we got true
uh we can also check if two values are
not equal example let's say I just want
to make sure that X and Y are not same
and the way you can do that here is by
saying not equal to so when we say not
it simply means it will uh when you say
exclamation it simply means dot so not
equal to Y and with this if I try to
compile and run you can say we got true
so even this is working but what if you
don't want to check for less than and
greater than you want to check if the
two values are exactly equal so in this
case normally in mathematics we use
equal to but that will not work here so
you have to use double equal to so you
are comparing x with Y and they should
be equal clear the screen compile and
run and you can see we got false the
reason we got false is because we have
both the different values so if I make
it same now and if I run this code
compile
and run and you can see we got true so
basically uh we we have different
operators and this will be used a lot in
the upcoming sessions uh so it doesn't
matter what type of programming you do
see when you say your computer has a
brain you know we have to decide based
on some values of course I have just
checked it with integer you can try it
with float as well in fact maybe I can
try with double so I can simply say
double here and I can say this is
8.8 and I can say double which is let's
say six maybe nine point eight and I can
just check if they are less than equal
to and of course I want you to try
different values there
and compile No it should run and you can
see we got true but if you check with
the greater than symbol this should give
you false
and we got false so basically whenever
you have a primitive value uh this
actually works uh maybe once we start
with string we also try to compare the
string values and let's see how that
turns out to be but this is your this is
how you do your traditional and
traditional operator checking with the
help of relational operators we got less
than greater than equal to symbol which
is double equal to not equal to that's
one yeah so this makes sense right but
what if you have two conditions example
let's say I got this values and now I
have int a equal to 8 and int b equal to
6. so I want to check if I mean I want
this x to be less than y and I also want
this a to be less than B I want to check
both the operation
and the thing is when we say I want to
check both the things should be true
then only it should print true how will
you do that how will you combine two
different uh operations or two different
checkings
so we are done with the arithmetic
operators and relational operators right
then we had one question what if you
have two relation operators and which
will result in true or false right uh
and then you want to combine them so you
want one true or false out of two or
three true or false so what I'm saying
is let's say I have two variables here
which is x y and also we have one more
commission which is a and b and then I
want to check if I mean I want X to be
less than y and I want a to be greater
than b uh this might result in two and
true and false or it might result in
true and false what I want is the output
of I I want is I want output of this two
combined can be either true or false but
I want the combined output irrespective
if they are a true or false individually
so how do I combine this
now to combine these two different
conditions we can use a logical operator
in between example uh this logical
operator can be and or I mean and the
second option is R so it can be and and
all now what exactly it means
see if you want that your output to be
true so let's say if you are out if you
want your output to be true
so you can use if you can say Hey you
know I want both of this to be true then
only I want true or you can say if any
of this can be true I want it to be true
now this is very important in terms of
computation So when you say your
computer is smart it's because of a
computer can decide based on multiple
conditions so to do that we use
something called a logical operators so
what we do is uh again this concept is
coming from mathematics is not a
programming concept it is coming from
mathematics
where you can use something called a and
operator we can use odd operator or we
can use a not operator which is which is
the exclamation
so the and operator in programming we
represent that with the help of and and
the odd operator so we use Ampersand for
and and we use a pipe for odd so we can
use Ampersand which is and we can use Pi
property which is or or we can use the
exclamation mark for not
okay so how do we decide what could be
the output of two operations so let's
say the first operation gives you true
the second operation also gives you true
so maybe you can come we can do that
with the help of these two conditions if
both are true then what should be the
output so the output will be true again
I'm talking about in terms of and
operation if one is true one is false it
is false if one is false I mean the
first one is false second is true again
it is false and if you want if you have
both of them as false again it will give
you false now when you want such type of
output when both if both are true then
only should be true then we can use
something called and and operation here
but what if you have a different set of
my set of things in your mind uh let me
just divide this and the second set
would be let's say if the first one is
true and second one is also true you
will get true if the second one is true
so the first one is true second one is
false it will give you true if the first
one is false second is true it will give
you true and if both are false it will
give you false if you have a condition
or if you have a requirement where if
any of them is true then it should be
true so example if you can see if any of
one so of course both are two that's
great but if even if you have one true
that's true even if you have one true
that's true even if you have one true
that's true right but if if you have
both false then it will be false now if
you compared with this and when you have
both true it will give you true if any
of them is false you can see if there's
a false you will get a false here so
this is your and and odd so that's how
you can combine we have one more here
which is not now not basically used to
reverse the thing example if you have
true and if you want the output to be
false and if you want if you have false
and if the output you want is true then
you will apply a not operation now apart
from this we have one more which we have
not talked about
which is xor again we'll talk about that
in some time but then we have three
basic operations here we have and or and
not so basically how you combine this if
you want to do that in programming of
course you can also use and operator or
pipe or you can use not directly the
other option you have is something
called a short circuit so instead of
using and you can use double and instead
of using or you can use double or and
not is as it is we don't have to do Nots
there and now what's the use of this so
first of all let's talk about and so
let's say if you have X
rest X is greater than y and if you say
and here and you can say a is less than
b so we have these two conditions here
and I want both them to be true and
that's where you want the output to be
true so example if you have a Boolean
value which is R here so you can say R
is equal to X is greater than y and a is
greater than b if in this case if both
are true the output is going to be true
right but if you what if you use R here
so if I remove this and if I put up R
here if any of them is true it will give
you true
as simple as that okay now why do we
call it a short circuit the reason is
let's talk about R in R see the point is
if even if you have one true the output
would be true right so if the first
condition itself is true it will not
even check for the second one
Beauty right I mean you're saving your
time that's why it's called short
circuit you are saving the time if you
are taking a shortcut
and you will say hey then what happens
when you have and here so let's say let
me put
and now in this case even if so let's
say first one is true of course it will
check with the second one but what if
the first one is false if the first one
is false it will not even check with the
second one because the output is going
to be false right so that is why it is
called short circuit okay so from this
point we are always going to use short
circuits and an odd instead of using a
single Ampersand so it can be you can
say double Ampersand for and double pipe
for or and of course not will remain not
so example let's say if you already have
a Boolean value which is R so I can say
R and if if you want to save that value
in s so whatever value of R you will get
you will save that in s example if R is
t s will be t but what if you put a
Ampersand here so but what if you put a
exclamation here
so in this case if this is true if R is
true it will give you false it will give
you a reverse value and this is very
beneficial when you start working with
the uh project where you have future you
have a data and if you want to do
something related to the data So based
on the data you will change some you
will do something you will change the
condition all the stuff
okay this thing looks cool here but how
will you implement this in the actual
code like that's what we're going to see
now so if you can see uh I of course I
have to go with the same variables I can
say int uh X is equal to let's say seven
and in fact you know uh let's let's do
it on your line and I will say int Y is
equal to 5. so we got these two values
and then apart from this I want two more
variables let's say A and B so I will
say int a is equal to 5 again and end B
is equal to nine I'm just getting random
numbers here and what I want to do is I
want to save the data in a Boolean
variable so I will say Boolean result
and let's see what the value you're
getting
so first I will declare it here and I
will also print the value for this
okay so basically we are trying to print
result here but then I want to perform
some operation on this so I can say if x
is greater than y okay I'm just checking
for one thing and now you know we have
done this multiple times I will just
compile this code and run and you can
say we got true because the value which
of X which is 7 is greater than the
value of y which is 5. but then I want
to put one more condition here and I
want both of them to be true if I want
to get the output as true so what you
can do is you can use Ampersand double
Ampersand here and you can say a is
greater than b now if you can see the
first condition is true okay this will
give you true but the second one the
second operation here will give you
false now what do you think is the
output think about this and let's see
now the output which I'm expecting here
is false let's try and yeah we got false
is because the first one is false
so the first one is true second one is
false so in this case you both need to
be true example if I make this as less
than of course you should not check
change your condition you should change
your values but just we are learning
into we're doing we are learning right
so it it's fine it's fine
now let's compile this code and run and
you can see we got through since both
are true it's true
but what if you use a pipe here now pipe
simply means R right so even if you are
so let's say that both the conditions
are true now and both these operations
are true
run and you can see we got true but what
if let me make the first one as
false right so you can say we have 7 is
greater than 5 so this will be false but
the second one is true right but still
if you compile this and
run and you can see we got true right so
this is how you use and and all when you
have multiple uh relation of course you
can add more you can also add one more
pipe here by saying the value of a
should be greater than one
that's your choice how many pipes you
want to add compile and run and you can
see it works uh so this is how you use
and and or what about not operator here
so example let's say
I will only say a is greater than b now
what do you think what the output is so
if I compile this code
and run and you can see we got false
that makes sense right because the value
of a is smaller than value of B
but what happens just before printing
result I'm saying not so whatever result
of whatever value of result is we are
just we are just doing the opposite of
it if this is true it will give you
false if this Falls it will give you
true
and if I compile and run you can see we
got true it's because this was false the
Oliver once was and now when I say
exclamation result it will give you true
so as I mentioned before it's very
important once we go forward towards
conditions I mean if else for loops so
this multiple conditions or multiple
operations which will result in true or
false will be very help very helpful in
this video we'll talk about conditional
statements now basically what happens
you know when you say your computer can
think of course we have a lot of
different Technologies now we have AIML
right which which can help your computer
to think right uh we are saying AI will
change the world but if you go to very
basic of AI or any computer I can say AI
is an advancement in terms of computer
which can think but if you can go to the
base of it we have one important thing
which is the flow is depend upon true or
false example let's say let's say when
you execute a code so what happens is
whenever you execute a code the flow
goes in this way let's say there's a
flow going on and suddenly there's a
point here so that let's say at this
point so this is a flow of the code and
at this point you decide okay if the
condition I mean if based on something
if it is true I will go this way if it
is false I will go this way or maybe
based on some other condition I will go
this way so what happens you know your
flow of your execution actually changes
based on what you decide at that point
and even if you think about Tesla cars
which is uh maybe I need driverless cars
but which moves and based on some
conditions the speed will increase the
based on some condition the speed will
decrease based on some condition uh the
the car will take a halt but if there's
a object in front of a car at that point
the car will stop right so this is a
point where his decide hey it's time to
increase this speed of a car so maybe
you can say based on some condition
let's increase the speed of a car uh
decrease the speed of a card or stop the
car so based on some condition you
decide the another flow now how will you
do that in programming and that's where
we have this option of conditional
statements so what you do is you write
statement statement statement and then
you decide I will execute this bunch of
statement
based on some conditions so here we'll
be having a condition if the condition
is true
and of course we have talked about
Boolean values we have seen relational
operators logical operators if you get
true you will execute this particular
block here I mean this block if it is
false based on something I will execute
this set of lines right so should we
execute this lines or this lines will be
based on your condition now the way you
can do that in programming with the help
of if else now this is similar to most
of the languages if you are coming from
other any other language maybe you have
seen this if not don't worry I will talk
about if else in this particular video
to understand that let's head towards
our code here and as you can see uh we
have we have a demo code and basically
by using the same file here I want to
basically do something based on a
condition so let's say I have a value of
x here which is 8 okay a simple value
maybe I want to print hello or buy based
on some conditions so so I will simply
say
system.out.print and then I will print X
here
okay in fact I want to I don't I want to
point hello
and then I also want to print buys I can
just reuse the code which I've written
here
with a proper indentation yeah and then
I want to say bye now of course if you
execute this particular code here if I
say demo dot Java and run you can say we
got hello and buy both what I want to do
is I don't want to execute both the
statements I want to execute hello based
on some condition if that condition is
false I don't want to execute hello I
want to execute the buy statement
so at this point I want to decide now
based on what
so for this example I want to test based
on the value of x so I can say if the
value of x is let's say greater than 10
maybe I'm just taking an example here if
the value of x is greater than 10 in
that case I want to print hello
so and then if it is false
I want to execute the Buy
okay
so maybe at this point let me just
comment this section let's say I just
want to print hello only when the value
of x is more than 10 okay and to start
with let me set the value of x as 18
which is greater than 10. so what I want
is at this point so we can draw them
this we can say okay the value of x is
18. so if you go for the condition so if
is a condition here or it's a condition
statement it will check the point here
which you mentioned or with the
condition which you mentioned if it is
true it will execute this statement or
it will not execute the statement now of
course that's true so if you go back
here and compile and run you can say we
got hello
so this is basically the Syntax for if
so how it is syntax we have to use a
keyword called if and then in the
bracket in the round bracket we have to
mention the condition see ultimately if
is not concerned what type of operation
you are doing here if is just concerned
is it true or false so even if you give
a true here
if he's basically happy okay so if don't
want a operation that if says you give
me true or false I will execute example
if I say false here
and if I compile run you can say it will
it is not printing hello why it is not
printing address because we are saying
false so when if C is false here it says
okay I don't have to execute the block
whatever is written under if okay so
there's a space here if you can see
again that is optional even if you
remove that that perfectly works because
Java is not dependent on any indentation
uh by any chance if you're coming from
python in Python we do that we give a
tab to specify that it's an it's a part
of the eve Block in Java we don't do
that
okay I could have simply used a meme
from Avengers you know it says we don't
do that here okay anyway so we you can
see we got false and we are printing
hello that perfectly works I mean of
course it is not working because we got
false but if you make it true it will
surely execute compile run and you can
see we got hello
right now uh what if I just want to go
back to my condition the value of x
should be greater than 10 and for this
as well
of course we want the value to be true
and it should print hello and it's
working but what if the value of x is
not 18 it's 8 which is false right 8 is
not greater than 10 so it will give you
false and that's where you will not see
hello and you can see we don't have
hello
okay so that's how you can use if of
course you can put multiple conditions
here if you remember we have talked
about logical operators so we can say uh
the value of x should be greater than 10
and I want one more operator and so I
want to condition basically and I want X
to be less than 20. so I want the value
to be in between 11 to 20. I want 20 to
be included so I will say equal to
so the range now okay we can also
comment something in programming with
the help of double slash uh which will
not be read by the programming or the
compiler
so the value accepted value for a x now
is from 11 to 20. uh because we are
saying greater than 10 which is the
value above 10 which is 11 and less than
equal to 20 which is including 20 okay
and now I'm saying and here
and let's make it 18 again so if you can
see it will surely work and we got hello
right so we can basically put multiple
conditions but what if the value of x is
8 or maybe I can say 28 which is not
less than 20. so this is true X is less
than x is greater than 10 that is true
but X is less equal to less than equal
to 20 no that's not true so this will
result in true and this will result in
false so what's what do you think the uh
end result would be so true and false
will give you false remember we have
talked about that in some table in fact
that table used is called as a truth
table okay
so now what I would do is if it is not
printing hello I want to print by so I
can just remove this
and if I compile this code and if I have
this code you can see we got by hello I
mean the hello is not there because the
condition is false
but what if I make it 18 now of course
that's true so what I want to do is I
just want to print hello I don't want to
print buy because if you run this code
and if you see the output we got hello
and buy both we don't want a buy in this
case
so what you can do is if you want either
this or this you can use uh one more
thing here one more qubit which is
called else so normally if else works
together you can you can also write if
alone
or you can say if else okay so there's a
compulsion to have if when you when you
want to use else okay else cannot be
alone
okay that works and now if I uh compile
this code
and run you can see we got hello but
what if you make it 28 at this point we
it will only go for
compiled one you can see we got by so
that's how basically we can use if else
so we have if we check for the condition
and then we can also write else in fact
in the next video in fact let's try to
do one more example here so let's say I
have the value of x as let's say 5 and I
have a value which is Y which is which
is seven okay so we got two values and
maybe these two values are coming from
the user so what I want to do is I want
to print the maximum of these two so if
x is greater than y I want to print the
value of x if Y is greater than x I want
to print the value of y so how do we do
it so basically I want to print the
value of X and Y so I can say system
dot out Dot println and I want to print
the value of x
and let me just reuse the code
I want to print the value of y but if I
just try to print this without com
without checking any condition it will
print both what I want to print is I
want to print the greatest number from 5
and 7. so in this case of course this is
a very simple examples and I'm just I'm
on purpose taking simple example is
because at this point it's important for
you to understand the concept not the
complex operation right so what I can do
is I want to print either I want to
execute either this statement or this
statement so whenever you have this
condition where you want to execute a
one statement or some block of
statements always go for if else
so I can say if and I can check if x is
greater than y that's what you are
checking right if this is true I want to
execute this particular statement
else
I want to execute this statement that
simple right so that's how we can use if
else and if I compile and run you can
say we got seven
but if you would change the value let's
say if I make the value of X as 8. of
course the output should be eight and
that's what we got
now one thing to remember here whenever
you have one statement under if or else
you don't need the curly brackets and
you can say we don't have it but what if
you have multiple statement example
let's say here uh the way we are
printing X let's say I also want to
print uh thank you okay in double quotes
I will say thank you now you can see we
have two statements inside if so I want
to execute this two
when the when this condition is true the
moment you have two more than one
statement you have to make sure that you
put the curly bracket so you open the
packets and you closed it and this thing
was very very important whenever you
have if or in future when we work with
loops and some Advanced concept as well
at that point if you have multiple
statements you have to put curly
brackets if it is only one statement you
can skip it
okay so yeah that's it from this video I
hope you enjoyed it before that
uh let me just
go and you can see we got the output so
that's it from this video in the next
video we'll try to expand this logic
more because in this video we were able
to compare two numbers what if you have
three numbers
that will be challenging right and if
you want to you can just try with three
values without watching the next video
and let's see how you do it see you in
the next video so we were able to
compare two values now it's time to
compare three values so let's say we
have int x equal to 8 into y equal to 7
and int let's say Z is equal to let's
say five or six let's see and I want to
print the greatest of these three now do
you what do you think what could be the
solution here
see one thing we can do is we can
compare all the values but at one point
you can compare only two values right
example we can say x is greater than y
we can't simply say x is greater than x
y and J okay that will be invite syntax
let me just show you that if I try to
compile this code you can see we got the
error so what could be the solution of
course we can't do this but we can do
one more thing here can we say when when
we are saying let's compare for X so at
one point you can compare if x is
greater than y and J both
and we have done that right so in one if
condition we can say x is greater than y
and x is greater than Z okay but then
don't you think these are two different
conditions and if you want to combine
them and I want both of them to be true
in this case we can use and and we have
seen this right
so basically we are doing an and
operation here for this condition and
this condition so if this returns true
and this returns true it will execute X
in fact you know just to simplify this I
just I have put the
curly package in the last video let me
just remove that
just to keep it simple
and now you can see we got this
condition so if this is true it will
execute X that means X is greatest that
makes sense right but what if in fact
let me just run this code if this works
properly
uh clear first and then compile
and
run you can see we got 8 because 8 is
greatest
but what if the value of Z is nine and
if you compile this code now and run it
says seven oh that's weird that means
the code is not complete see at this
point if if is false I mean if by any
chance if this is false that means we
now we have to go for Y and Z we have to
compare them how will I do that
this was simple how will you compare the
gain because in else we don't put a
condition right
but what if we can so what if we can say
else and again we can put an if
and in this if we can say Y is greater
than x
and or not this and the logical and
and then Y is greater than Z so
basically what we're doing is in the
first case we are checking for x if x is
greatest the second case we are checking
for y if Y is greatest at this point let
me just make y the greatest which is 17
so of course it should print 17
run you can see we got 17 but what if
okay first of all let's do a draw it on
here so what happens is
it starts from this condition if the
value of x is greater than y
if that is true it will check for the
next one and as you can see here itself
it is getting false so the moment you
get false here it will not execute the
block what it will do is it will go next
it will say okay we got else here
it will execute the else block but an
else is not a simple else it is else if
one more condition here which is
checking for y if Y is greatest it will
print y but what if Y is not greatest it
is z here but still if you compile this
code you will get nothing you know why
is because we are not printing Z
anywhere so what you can do is you can
you can do one more else here for Z so
if this two are false of course you will
execute the else block I can just simply
copy this and paste it here in Aisha of
saying copy paste I can I can say code
reuse that makes much more sense and I
can say Z and now if I can compile and
run you can see we got nine
now this makes sense right so if both
these conditions are false it will
execute the S block okay and that works
now you can just change the values in
your machine first of all copy the code
and whenever you change the values it
will surely work but there's one more
thing
if you can think about this when you
execute this one and if this gives you
false don't you think the x is small now
compared to other two values
so in that case when you check for y why
we have to even compare a y with X and
if x is smaller right so now we just
have to compare y with C we are just
saving one in one of one operation here
and it's very important when you say one
one operation you are saving time you
are saving resources so try to try to be
a efficient programmer not just a
programmer and that's what you do you
check what is required which is not
required and remove all the unnecessary
code and once we have done this compile
the code and run you can see we got nine
and you can change the values it will
surely work so what we have done in this
video is we have talked about if else if
else and that's how it works now once we
have talked about conditional statement
in fact in that we have talked about if
and then we have also seen how do we use
if else and then we have worked with if
else if now for certain use case we have
a shortcut for it and it is called a
ternary operator now if you want to use
if else on the same line or if you have
a shorter condition and if you can write
out that on one line why not so what I'm
saying is let's say if you want to check
if a given number is even or odd how do
we do it it's very simple what you do is
you uh first of all you take a number
let's say another number is 4 and if I
want to check it this is even odd so
using IF else how you do it is we say if
and we check for the condition if n mod
2 is equal to equal to 0 that means it's
an even number right so what you do is
you come back here and you can you don't
need curly brackets because I want to
add only one statement and I want to
store that in a variable now basically
we can use a Boolean type here or we can
use a string as well well so let's say
I'm using a string okay and based on
this string or maybe let's let's keep it
simple so what I will do is I will not
print even or what I want to do is I
want to set the value which is in X or
maybe I will put that in result and I
want to put the result by default it
will be 0 but based on this if the
number is even or odd I want to set the
value for result if the value if the
value is even I want to set the value
for result as 10 if the value is let's
say odd I want to set the value for
result as 20 okay so for even it is 10
for odd is 20. how do we do it so in the
if condition you can do you can say
result is equal to 10. so if that's a
even number user result equal to 10 and
if in the else part you can set result
as 20. so what we are doing here is
based on some condition I'm assigning a
value now this is one way and of course
at the end I can print the value of this
as well I can say I want to point result
nothing fancy came simple stuff and then
I want to compile this on once I will
say Java C demo dot Java and Java demo
and you can see the output is 10 why the
output system is because the phone here
is a even number what if you make it
five now we are making it odd right so I
can just go back here compiled one you
can see we got 20. so this is working
now what you can do is you can convert
this code into something called a
ternary operator now how it how it works
let me just comment this section
see ultimately what we are doing is we
are saving the value in result variable
in both the thing we have the same thing
right
if it is if is it true then we will set
the value for result if it is false for
the else part also as a result so can we
do this can we say result is equal to
the result can be 10 or it can be 20
right but how will you do it how will
you check for the condition so what you
can do is you can directly run a
condition here so you can see if n mod 2
is equal to equal to 0 if this is true
then we have to do something or or will
do something so we can use something
called a ternary operator here now how
it looks like so turning up it looks
like this let me just write that in
comments so we have to use a question
mark and a colon so what is this
question mark and colon so whatever
condition you have it might return a
true or false so you can put a question
mark you can ask hey is it true or false
if it is true then execute the part
which is after the question mark which
is 10. if it is false you have to
execute or you have to take the value
which is after the colon okay I will
just give a space here so that it will
be much more readable right so what we
are doing is we are saying for this
condition if this is true in that case
we turn 10 if this is false in that case
return 20. so you can see out of all
these four lines of code we are doing
that in one line with the help of
tunnelio operator of course it is not
suitable for every evils it's not like
you will say hey from now I'm not going
to use zfl that's not that's not the
case this is suitable for some examples
this Theory it makes sense because we
have a very short assignment and
ultimately you are sending value to
result so this makes sense I can just
compile and run you can say we got 20
because the value is odd but if you make
the value as even let's say 4 again
and if I compile and run you can see we
got 10. so this is how you can basically
use a ternary operator now if you
remember what we have used if else if
you can also do that here I would
request you to try that put one more
condition here and try it out for
multiple use cases in this video we'll
talk about switch statement now to
understand switch statement we have to
go for an example so if you go back to
your code what we have here is let's say
we have a integer value and the value of
n is 1. now the value of n could be from
1 to 7 and might be you have guessed it
so when I say one two seven it might be
the number of days and you are right so
basically what I want here is if the
value of n is 1 I want to print Monday
if the value of n is 2 I want to print
Tuesday so based on the value of n which
can be from 1 to 7 I want to print the
day of the week how do we do it so of
course you can just simply print the
values right you can say hey I want to
print Sunday and you can just uh copy
paste it or maybe copy pasting is not
the right word you can say uh code reuse
so just ignore this xci just just
suggestion given by the vs code we can
say this is Monday and we can just paste
it multiple times so this is Tuesday
this is Wednesday Thursday Friday and
Sunday you know what I want to keep
Sunday as a last day because that's what
we say right weekend the Mondays the
videos will start from Monday okay so I
want to print this based on the value of
n at this point if you just run this it
will print it will print all the values
I don't want to print all the values I
just want to print uh one day based on
the value of n so of course you can do
one thing you can just check with the
help of efl so you can check if the
value of n is 1 you can just print
Monday if the value of n is let's say
you can say else a fear if the value of
n is 2 in that case I can print uh
Tuesday right we can do that at least
let's do between Monday and Tuesday
because that's what you're putting into
effects and if you run this code with
that changes you can see this printing
Monday it is not printing Tuesday
because Tuesday is in if else and you
can apply that in all the conditions
here and all the statements you can
simply put if else and you can check for
n is equal to 3 and then list goes on
right this is one way
there is another way using which you can
do this in fact you know what I can do I
can just simply complete this uh code
and here it should be 3 4
5
6. you know for seven it actually makes
sense to not even mention the condition
because if none of it is matching of
course it will be Sunday right uh so if
there's no office that Sunday okay so
basically this is what you can do here
uh but don't you think there should be a
good way or better way of doing this so
instead of doing if else everywhere and
at the end of else we have a good way
which is called a switch now what switch
will do example when we talk about
switch it will switch between the ports
right uh example in networking concept
as well we use something called switch
so here what you can do is we can use a
switch now based on a value it will
execute a particular case and that's why
most of the time we say it's a switch
case statement
okay just follow me so what I can do is
instead of using this if else I can
simply rewrite everything in a switch
block I can say switch switch and in
this switch you can pass the value which
is n in this case and then you can write
everything in this block okay how do we
mention that in this blog I have written
Capital switch my bad what you can do is
you can put all this thing inside this
block the only changes instead of saying
if
we we don't for the condition we don't
fully check for the condition we just
match we try to match the case it can be
something like this we can say case one
colon so whatever value you have passed
if this is matching with the case
example if n is matching with a 1 it
will execute this statement same applies
here in fact you know I just want to
give a tab to everything else and then
here I can just say case to
for this and let me just complete this
thing for all
okay and then of course the number has
to be changed so we can say this is
three this is 4 this is 5 this is 6 and
this is seven okay so we are trying to
match with all the cases what I will do
is I will start with seven and let's see
what happens the moment you make it
seven we are basically trying to match
the cases so what happens is when you
execute this it will go to the switch
statement and switch says okay I got the
budget which is seven and now with this
7 I'll try to match with all the cases
here so it will check if the value which
is passed which is 7 is it matching with
one no it will not execute the block is
it matching with two no is it matching
with three no this goes on it goes on it
matches with seven the moment it matches
it will execute this statement which is
print Sunday and it will do that so if
you run this code example if I compile
this and run you can see we got Sunday
simple stuff right and this one looks
much better than the efls because we are
checking for the condition multiple time
here we are matching the case Okay so
this looks better right and it also
works better compared to e-fills but
those of you there's only one issue here
the issue is what if the value of n is
2. now what do you think the output
would be think about this and maybe in
your mind you already have an answer so
what I will do is I will just compile
this code and run this code oh that's
weird we were expecting Tuesday but we
got all the values the reason is when
the moment your switch case matches with
a case example it will check do is it
matching with one no it will not execute
this block is it matching with two yes
the moment it matches the case it will
execute the block for sure and it will
just try to complete the entire switch
statement it will execute all the cases
it will not try to match again because
it's already matched oh that's an issue
right so what I want is I can simply ask
my switch hey you know once you match
with one of the case just come out of
the switch block and the way you can do
that is by using a special keyword
called break now break is very important
because this will be used multiple times
for different concept what we are doing
with break here is it says simply come
out of the block now once you match with
any of the case just come out and of
course for that you have to put break in
all the cases I will just copy this I
will try to reuse the code here and
paste it everywhere okay now what we are
doing is the moment it matches with the
case it will jump out let's try this now
compile run you can see we got Tuesday
it is not printing all the other blocks
because the moment you print Tuesday it
will simply jump out because we are
saying break that looks cool right now
now there's one more important thing see
for the last case we are still checking
right or maybe we can have one more case
what if the value is 8 is not in one
coming in any of the case here in that
case what you can do is you can do
something called default case if none of
the cases are matching you can do
default and you can print enter a valid
number I mean you can print any
statement you want I'm just saying enter
the valid valid number and you can see
their value here is 8 so it should print
enter the value valid number and that's
what you got enter the valued project
number so this is how basically you can
use this switch statement
now with the recent versions of java you
can actually avoid using break there's a
different syntax we can use but again
that will see in a separate video of
advanced Java concept where New Concept
has been introduced in new versions
right but at this point this perfectly
works and in most of the companies they
are still into Java 8 so let's stick
with the syntax so try it out with
different examples and you will be good
to go one of the most important thing
about programming is you can do certain
things repeatedly of course we have
talked about different things now in
normal software development basically
you work with data and that's why we
have variables so basically you can
store your values in normal application
you decide based on some values and
that's why we have seen if else we have
seen internally operator we have talked
about switch statement but then there
are certain use cases where you might
want to repeat the same thing multiple
times in fact there are a lot of memes
available which says you know in our
school time when when teachers used to
say write is 100 times
what if you can just do that with the
help of software write the same sentence
multiple times
not manually but automatically it should
reiterate it should iterate itself
and the way you can do that in
programming is with the help of loops
Let me Give an example here
so let's say I have a code here and I
want to print something let's say I want
to print here hi and I want to print
this High multiple times not once but
multiple times example if I run this
code now it will only print hi once
if I want to print that multiple times I
can just copy this and I can just paste
it multiple times here let's say four
times and if I type it four times of
course it will print the output in four
times we don't want four times what we
want is we want to write this once and
it should call itself multiple times
the way you can do that is by removing
this part
and by doing something maybe I can just
say uh I can just write in comments I
can say repeat this statement
four times maybe it's something like
that of course this will not work
because comments are normally ignored by
the compiler but how do you do that how
do you mention Java hey I want to run
this multiple times
and that's where the concept of Loops
comes in a picture
so we have a concept like Loops which
will reiterate the same thing and there
are multiple Loops available in Java
with different languages we have the
same thing or we can say similar thing
so we have something called a while loop
we have do while loop and then we have a
for Loop now mostly we use a for Loop
but then we'll start with while and do
while and they have their own use cases
it's not like just because we have for
Loop will not be using while and do
while they have their own use cases now
just to give you a hint
maybe you want to repeat certain things
multiple times but then what will be the
condition maybe you want to print that
100 times
that means there is a finite number five
times ten times eight times fifteen
times twenty times 25 times 100 times
or maybe you want to do that do
something based on some condition
example uh do something till I press the
enter button do something till the
system is alive okay something like this
so maybe you want to do something finite
times or maybe you only do something
based on some condition uh and for that
we have different types of Loops
available
so what is loop basically if you want to
do the same thing multiple times you use
Loop and there are multiple Loops
available while loop do while loop and
for Loop and there are multiple versions
of for Loop available but we'll see the
simpler version which we call normal for
Loop and yeah that's what we have will
explode all these Loops we have talked
about the need for Loops right and so we
have decided that if you want to repeat
something Loops can be a good thing and
we also talked about there are different
types of Loops right we have while loop
do while loop for Loop in this video
let's try to understand the first Loop
which is while loop so we'll go over
this go for the same statement here if
you can see we are Printing High and
again as I mentioned before ignore this
x this is a suggestion given by your vs
code uh this is what we are typing just
high and what I want to do is I want to
print this High multiple times so what
we can do is we uh we can say Hey you
know Java I want to print this multiple
times Java will say okay
the first thing you do is you put this
in a block of course it's not compulsory
when you have one statement but just to
understand just to get started we are
putting that in a block now and then of
course we have to follow into
indentation as well and we are doing
that now what we can do is we can say
Hey you know Java I want to run this
five times so Java will say okay if you
want to repeat you have to use a keyword
called while now in English as well we
normally use while to say repeat
something or while it is true do that so
here we can say while it is what in this
bracket you have to mention is it true
or false now basically that's how Wild
works so if you say true it basically it
will just keep printing this High
because we are saying true it says okay
while I'm true I will keep printing it
so that's why if you just run this code
by just by mentioning the
while
you can see we are getting high I just
keep printing okay it's it's not
stopping if you can see if I'm trying to
scroll down it is continuously happening
and maybe it will uh fill my Ram it will
crash okay I don't think so but let me
stop this execution otherwise there will
be an issue so what we can do is I don't
want to continuous this for a long time
I want to do that for a particular
condition maybe I want to say I want a
counter which will start from one and it
will stop at five oh when I say counter
it means I need a variable where I can
store the value so what we can do is
here I can just come up and I can say
int I is equal to let's say one now most
of the time when you use Loops you will
be using a variable name I it's not
compensative we can use any variable
name but it makes sense right because
normally when you go inside the while
you are executing something you are
changing the values of the eye
you basically increment it right so it
makes sense to call it as a iterator
which will iterate so I iterator makes
sense and that's why most of the time
you will say i j but as I mentioned you
can use any variable of your choice so
we are using I here which is I is equal
to 1 and then what we can do is every
time you run this loop after Printing
High you can just increment the value of
I
oh but then how do we increment and we
have seen that right we have a concept
of I plus plus so I plus plus will
simply increment the value of I okay
that makes sense and oh how do I check
for the condition see it makes sense now
because I is 1 and every time you run
this Loop the in the I value will
increase right so if you run this while
for let's say five times it will
increment the value of I let me show you
what I will do is I will print hi as
well as I will print uh maybe you can
you can print both the things I say on
the same line you just have to give a
space after high and I can give a plus
symbol so when you want to concatenate
two different things High and a number
we can use a plus operator yeah plus
Works in that way it works for addition
as well as it works to concatenate two
things
and here I'm writing I now let's see
what's the output is again I have not
changed the condition so it will print
infinite times
but I just want to see what happens if I
compile this code
and run you can see the value of I is
incrementing continuously
and you can see it so fast depend upon
your machine speed as well and let me
know when you try on your machine how
fast it is so what I want to do is I
want to stop this somewhere so we have
to apply a condition how do I stop it so
we have to say if I is less than equal
to 4 so what it will do is it will check
for the condition remember we have
talked about this in relational
operators it will continuously check for
the condition so what how it runs is
initially it will set the value of i as
1 and then in the while loop it will
check if the value of I which is 1 is
less than 4 yes it will continue it will
go inside the loop it will print high it
will also print the number which is 1
and then it will increment the value of
I what next it will go back to while
loop because and again it will check for
the condition because that's a while
right it will continuously happening it
will again check for the condition where
it says okay I value now it's 2 so 2 is
less than 4 yes and it will continue at
at the end when the I value becomes 4 it
will check 4 is less than equal to 4 yes
it will print High and 4 as well so we
got four iterations and then it will
increment the value of I which is it
will make it five it will go back here
and it will check is 5 less than equal
to 4 false and that's where it will jump
out of the loop so remember this thing
the moment your while gets a false here
it will not execute this block cool
right now after saying all those things
let's try to compile and run and you can
see we got high one high two High three
and high four that's how while loop
works now with this I have a question
for everyone here and the question is
what if at the end I'm just saying as
out and I'm saying buy and with this by
I'm printing the value of I what do you
think what will be the output of I
okay try to guess it I'm just running
this code to show you the output compile
run you can see we got all the values
here but with by you got five you know
why is because
we got false here when the value of I is
5 and that's why you got the value here
now since I is declared outside the loop
the value will be maintained okay now
one more thing here I want to run this
in a debug mode let me show you how it
works in debug mode so what I can do is
I can go to run
and I can say start debugging okay so
there are some options okay for
debugging you have to basically you know
uh you have to set the checkpoints what
I will do is I will just set the
checkpoint here so basically debug is an
awesome feature in programming where you
can set the checkpoint this is where you
want to iterate one by one so normally
when you run the code it will directly
give all the output right what if you
want to see the steps so it makes sense
let me just clear this and again I will
go into run
and get into the debug mode okay so you
can see uh we are in debug mode now and
here on the left hand side we got
variables we got local a and I we have
two variables you know why we got a is
because of this a variable here but it
is at this point we want to ignore that
we want to focus only on I variable and
the value of I at this point is one you
can see that I is one but now if I say
step into you can see we got
system.winder it will print the high and
I the value of I which is one uh okay I
want to go step into now it will
increment the value of I you can see we
got the output as well we got i1 and
then when I say step over it will go for
the next step and you can see before
executing it the value of I is 1 but
once I execute that statement the value
of I now becomes 2 okay so that it went
back to while loop and this will keep
happening for I value 2 I value 3 I
value 4 as well the moment your value of
I become 5 here you can see the value of
I is 5 now it is checking and it falls
it it will jump out of the loop it will
print by with the value 5. so that's how
your while loop Works in fact what you
can also do is we can run a nested Loop
here now how an estate Loop looks looks
like let's say I want to print i1 and
then I want to do something else maybe I
want to print hello three times after
every high so let's say I'm Printing
High here and then I want to print hello
as well
and I don't want to print the value of I
anymore
or maybe let's print the value of I
let's see what happens if you keep the
value of I here and then incrementing it
here as well that makes sense but now
what I want to do is I want to
after printing this High I want to print
hello five or three times now in that
case I can simply say hello and I can
write the same statement multiple times
right that's how the loop works right so
I will say hello hello and you can see
we got hello three times but don't you
think we are doing the same thing
multiple times so it makes sense to put
that in a loop so I can simply say while
oh but what should be the condition can
I say I is less than equal to 3 no right
because see I want this hello three
times for every high so high we are
getting four times and for every High I
want Hello three times
so the same value will not work in that
case what you have to do is you need to
work with a different variable and I
will create one more variable here which
is called J and the value of J initially
will be 1
and then every time you execute this
while loop where it prints High
it will jump inside here it will set the
value of J as 1 it will set the value it
will check for the condition where J
should be less than equal to
3 and then every time you do that let me
open the curly brackets
and we can put this hello statement in
here so we don't have to put this thing
now I can just simply say hello and of
course I want to print J plus plus as
well and remember this thing we are
saying J plus plus in the inner while
loop and then we are saying the I plus
plus in the outer loop okay if you want
to understand this with an analogy uh
just go with an example of days in a
week so we have multiple days in a week
right so we have Sunday Monday Tuesday
Wednesday Thursday Friday Saturday
Sunday I've already mentioned you know
we we basically want Sunday twice a week
but anyway so if we talk about these
days every day we have 24 hours right so
if you say this is 1 pm on Monday again
the Monday gets over the clock will
start at zero right then zero one two
three four five six and then it
continues right as the date changes the
clock repeats in the same way once your
eye is incrementing it's like a days
Monday Tuesday the inner loop you can
imagine that's as a number of hours it
will keep incrementing but after three
it will go back to one because it will
complete the inner loop it will go back
to Outer Loop and again this is again
the value of J will become one let me
show you how it works let me just
compile this code compile and
run you can see we got high uh we are
still printing one here you know what I
will do I will also print J so that you
can see the value of J as incrementing
it
and let me give a space here as well let
me say clear
compile run so you can see we got high
one and then it is going for the inner
loop now so once you execute this High
it will go for the inner loop where we
are saying J is less than 3 so basically
it will print this statement three times
because the value of J is less than
equal to 3 so it will iterate three
times
and then again you have to go for the
outer loop so the the moment this is
false it will execute I plus plus where
it will make I2 it will go back to the
upper loop again it will say okay now
the value of I is 2 is 2 less than equal
to 4 yes it will go inside it will print
the value of high which is high 2. again
it will make the value of J as 1 and
that's why it is incrementing again
cool right so this is basically called a
nested while loop
so that's it from this video where we
have talked about uh how to create a
while loop how to use a nested Loops
using uh while loop now once we have
seen while loop it's time to move
towards a do while loop in fact before
we proceed first of all I want to remove
this breakpoint because we don't want to
debug anymore and I want to remove the
inner loop because we want to focus only
on the Outer Loop now
using this Loop we were Printing High
four times and then we are printing buy
as well let me also remove buy for now
and with this I just want to run this
code once again to see what happens
compile
run and you can see we got the same
output right
okay now what I want to do is uh when
you talk about while what happens is
when you talk about this line which is
line number seven it will assign the
value of i as one wait go for the next
line which is line number nine here
it will check for the condition if it is
true it will execute this block that
means if this condition is true then it
will execute otherwise if this condition
is false it will not execute the block
that actually makes sense right that's
that's how the loop should work but
there are some certain situation where
you want to execute this block even if
your condition is false at least once I
mean you want to earn this at least once
maybe something like uh you want to send
a message to your friend and if the
service is not available from your
friends and at least you should be able
to send a message once at least
okay so that you can get the reply the
user is not available or something like
that so what I want to do is I want to
execute this block at least once even if
the condition is false now when a second
condition is false what it means is
example is the value of I is 5. now when
you make the value of i as 5 and if you
run this code you can see will not get
any output is because the condition is
false
so what we can do is can we just cut
this part from here and put it after the
block
we can do this and we can just also give
a semicolon here because that's how you
end this statement normally when you
write a while at the start the curly
brackets becomes a statement but then if
you write while after the block we have
to end it first by the semicolon and we
have to add one more which is do so we
have to say do while
now what it does is it will execute the
block at least once even if your
condition is false now if you can see in
this situation first of all let me just
go with one again and let's see what
happens if you're on this code compile
run you can see we got the normal output
and this the same output we got when we
had a normal while loop as well but here
if you make this condition false I mean
if you say I is 5 now which is a false
con which will give you false here
but if you run this code or compile this
one you can see at least you will get
the output once this is important so if
you want to get the output even once for
even if your condition is false you will
be using two while so yeah that's the
main difference between while and do
while otherwise it works the same way it
executes uh check for the condition
again execute check for the condition
and list and the flow go on now once we
have talked about do while loop and
while loop let's talk about the next
type of loop which is a for Loop now if
you go back to while loop so let me just
remove do here and let me put this back
here and okay let me remove the
semicolon as well there is one more
thing if you talk about this while loop
if you can see we have three things here
the first one is we have initialization
we have a condition and then we have a
increment so basically we are doing
three things on three different lines
and if we talk about any finite Loop so
when I say finite Loop it means it is
starting somewhere it is ending
somewhere and we know when it is going
to end there are some Loops where you're
not sure when it was going going to end
example when the user says enter it will
end maybe the network goes off it will
end so based on some condition it will
end maybe you are trying to read a file
so in a file you let's say you have a
thousand characters and we don't know
how many characters we have so when you
open the file and when you try to read
each character so the the loop will end
when the characters end in the in the
file so we are not sure that's why I'm
saying you it can be uh not a infinite
Loop but somewhere we cannot determine
when the loop will end so at this point
we can determine right but anyway so we
have three things here we have a counter
we are initializing it we are checking
for the condition and then we are
incrementing it so what if we can just
write all these things in one line what
I'm saying is can we just pick up this
thing from here cut and paste it here
itself so on the same line we are
initializing the variable
and on the same line I'm give I can give
a semicolon I can say I plus plus
and of course we don't have to do that
here now
the only thing is while loop does not
support this syntax while it says I will
only for check for the condition
but then if you want to use this type of
syntax you have to use another type of
loop which is called a for Loop so in a
fourth Loop you can mention three
different statements in one line mind
you these are three different statements
why is because we are using semicolons
in between so this is one statement here
this is another statement and this is
another statement
and you can see I'm just pointing High
here the same the same code
I just want to check if this works
compile
run oh we have not got any output oh is
because the value of I is still 5 let's
make it one and by doing that I can just
compile this code and run you can see we
got all the values make sense right so
how a for Loop works so we have to set
the initial value which we have which we
have done here and then we have to check
for the condition and then we have to
increment or decrement so let's say I
want to print that a decrement order I
mean I want to print 4 3 2 1 in that
case I will start from 4 and then I have
to end
the eye should be greater than and equal
to 1 and I plus plus so the I minus
minus because we are decrementing it
compiled one you can see we got high
fourth High 3 High 2 and high one so
this works okay can we do something more
here actually we can uh what if you want
to start let's let's again go for the
increment part so let's say I'm going
for one and it should be less than equal
to 4 and then I'm saying I plus plus
see most of the time we'll start with
one itself right so that's how your uh
normal number system works as a human we
do that right but computer normally
start there counting from zero it's
because of the binary format uh because
then by the way we have zero to one in
fact in the number system also we start
with Zero versus zero to nine right uh
in fact once we start with the array
concept there as well the number starts
with zero so in general in computers the
number system starts with zero so we can
also say let's start with zero
but the question is if I start with 0
where I have to end it is it four or
five or three because we want to print
only four times right so let's keep it
four it which is equal to 4 and then we
also have 0 here so let's try to compile
and run you can see we got uh five
values it starts from zero and it is
ending at four
okay that is an issue how do I stop it
at three I want to print 0 1 2 3 that's
it four four iterations so in that case
what you can do is you can stop it at
three now this is something which will
take time for you if you're doing this
for the first time when you're starting
with zero you have to end before that
you have to end before the count so if
you want to do it four times you have to
end it at three okay now let's try this
I will say compile and run you can see
we got four times now one of the common
syntax you might be seeing in most of
the examples or if you're if you're
referring a book or online content you
can also stop this as four but you have
to say less than four because you're not
including 4 here you're saying less than
4 not equal to 4. so this is one of the
common syntax you can say it starts with
zero and it ends less than four and now
if you try this you can see we got four
values make sense okay
uh now let's try something else so Loops
normally work well when you try to print
some pattern or when you try to do
something repeatedly so what I will do
is let's try something
so what I would try is I want to try
this one I want to try this one I want
to try to print the number of days
I will say one two three four five
six and seven because we have seven days
and also every day I want to print
uh 24 hours
that looks good right we have talked
about this example right so what I will
do is first of all I want to print all
the days so I will say one two
seven including seven so I have to say
equal to and then here I will just print
the number I will say okay I will say
day one two three four uh imagine day
one means Monday day two means Tuesday
and and so on so if I try to do that I
will say compile and run you can see we
got all the days now with days I want to
print the number of hours
okay I know that will be tricky or maybe
we can we can actually print from uh 9
00 am to 6 PM because that's that's most
of the work hours right so let's say if
I want to build a calendar in fact I
don't want to print till seven five
makes sense because uh we have sixth and
seventh day as holiday so let's try this
I will compile and then we got five days
in this five years I want to print from
nine a.m to 6 p.m how do I do that so I
can simply print with the help of
statements I can say uh this is one
or 9 am
right or I will simply say nine and then
I can say 10 I can just print this once
again so this is 10 and so on right I
can print it till 18 because 6 PM is 18.
if you go for 24 hours of clock uh but
then don't you think we are doing this
thing repeatedly I have to basically
type so many lines
so of course we can use a loop here
right so what if we can use a inner loop
we have talked about nested Loops here
we are doing it with four so I can say
for and I have to give a count right so
I can say J we'll start with from where
now this is tricky should we start J
from one we can so I can say one and J
less than so many hours we are doing
here we are doing nine hours right so I
can say nine and J plus plus right and
then I can just give a loop open and
loop close and then we can print the RS
here now what hours are to print I
cannot print nine because nine is not
nine it will print nine every time okay
example if I show you this
let's say clear in fact what we'll do do
you know before printing nine I will
give a tab so that it will give some
indentation before it Sprints this is
what I was saying you can see we got day
one and we got nine hours here but then
it is printing 999 I don't want to open
999. maybe I want to put an attendance
here or maybe a calendar where we can
Mark whatever what we are doing going to
do
so what we can do here is I want to
uh say okay I should not be printing
nine after this space
I can say I want to print let's say
value of J but J will print from one to
nine let me show you what I'm saying
clear
compile
run so you can see it is printing one to
nine I don't want to point one to nine I
want to print from nine to eighteen in
that case can I simply add this with
eight because it will start with one so
one plus eight is nine right which it
will start from nine and every time it
will increment the value of J so you
will get some other values I will just
compile this and run
oh something went wrong okay now what is
happening here is we should have talked
about this before but it's if we are
never late right so what what is
happening here is we were expecting it
will print nine but what is happening is
when we are saying that we are adding a
string with a number it will coin
calculate right so here we were
expecting that J and 8 which is 1 and 8
will get added to get nine but actually
what is happening is it is getting
concatenated so we have to mention hey
you know uh instead of adding a string
to a number the number what you can do
is you can put a bracket here so I want
this to resolve by itself I mean this
should be solved in a separate way so
whatever number you are adding here 1
plus 8 will be a separate thing and then
you are concatenating that with a string
let's try that compile and run oh it is
working I guess no it is not working
actually oh okay we cannot add six right
because it's the 17th R which gets over
Okay so let's say we are printing for 9
hours which is from nine to five
okay which also includes the the fifth
uh the fifth 17th R okay that's tricky
okay in fact you know what should I do I
should actually print uh colon here or
maybe a dash hyphen from this R to this
R this is what happens when you take the
example randomly so I will say J plus
nine so what I was saying is this you
know uh from nine to yeah this makes
sense now so you can see we can we have
actually built a calendar for this week
so day one from nine to ten we can do
something here from 10 to 11 we can do
something here we can set up we can set
a meeting calendar something like that
uh so what I'm doing is we are printing
J Plus 8 which is nine and then J plus
nine which is ten for the first
iteration as the value of J increases it
will have different values here
okay make sense right so this is what uh
we have achieved in this example so
that's how basically your for Loop works
okay this is nested formula we have seen
that as well
okay now once you understood this let me
just comment this part I don't want to
do that I have a question for you now
think about this and let me know what
could be the sequence here
see when we write this in three uh in
the same line these three things how do
you think they're executing is it
something like this is getting executed
first and then this one and then this
one and later on after executing all
these three statements it is executing
this statement what do you think okay
let me give you the answer so the moment
you execute the for Loop let me just you
know this is the best time to run a
debug mode so I will say Run start
debugging taking some time to start the
debug okay so I will say step over so
you can see it is executing the uh for
Loop but we have not studied that yet so
let me start the for Loop the moment you
start off for we can see the value of I
is one it just check for the condition
as well
but it is not it has not incremented yet
because the value of I is still one so
that means these two things will be
executed first and then it will execute
the block
and then if I step over it will execute
the next iteration
in fact you know what I will do for the
next iteration I will say step into
the value of I is 3 okay it is
not doing that but anyway so it is
executing the body and then it is
incrementing okay
so that's what I wanted to show you cool
uh so Point remember it will execute the
this statement first it will it will be
done only once and then it will check
for the condition then we execute the
block and then it will increment it I
mean whatever you want to do in that
situation in that portion
in fact if you want to uh skip any of
this step you can actually so that what
if you want to skip this from here it's
your choice you can just keep it empty
the only thing is since you are skipping
that if you want to make it work you
have to say I plus plus of course you
have to increment somewhere otherwise it
will be an infinite Loop you can
actually skip the instruction part from
here and you can write it outside as I
mentioned your choice it's just that you
have to put the semicolon that's
compulsory you have to have two
semicolons there
and now let's
compile
run you can see it it works so that's
how you can work with fall I hope you
enjoyed so we have basically seen three
Loops right while loop do while loop and
forth Loop now the question is which one
to use in fact doing the discussion of
this loose we have talked about it which
one to use but just to summarize things
see if you have of course all the loops
works in the same way you can use any
any of them at any point but the thing
is if you know how many iterations you
want to go for example let's say if you
want to print from 1 to 100 you normally
use for Loop if you because we know the
numbers right because in photo we
mentioned all the three things the
initiation value condition and the
increment decrement part but what about
reading a file because in reading a file
we don't need a counter right because
when you read a file how it doesn't
matter how many characters you have you
have to pick up each character right so
there is no initial point it's just that
you will read the file the moment you
have end of file you will stop the loop
so using a while loop there makes sense
can I use for loop as a while loop yes
we can if you remember we have seen a
code where you can just give two
semicolons and in between the semicolons
you can put the condition even that
works
how when to use do while loop
now whenever you use a while loop and if
you think hey even if the condition is
false you still want to execute
something at least once dual makes sense
but expert my experience most of the
time you are going to use for Loop if
you want to read a file re-database
while loop makes sense and I have I have
hardly used do while loop in my entire
career but yes there there might be some
use cases where you have to use Dubai
Loop so which is the best Loop in terms
of frequency of use it will be for Loop
in terms of the usage for database files
Network while loop makes sense once we
have talked about the basics of java
it's time to move towards some Concepts
now at the start itself we have
mentioned that Java is object oriented
programming now what do you mean by
object oriented programming so when you
talk about object in real world
everything is object right in fact if
I'm using uh a pen that's an object if
I'm using a mouse that's an object if
I'm using a seller type I don't know why
I have sellotape on my table but that's
an object right so everything around you
is an object and the weird thing is in
the programming world even they treat
humans as objects but that's fine
everything is an object now everything
has two things in fact every object has
two things
an object knows something an object does
something example let's say if you talk
about this pen
this pen is an object right so this pen
knows something so when I say no
something it simply means it has some
properties some physical properties
right you can see this pen right so we
have a a color for this pen I'm very bad
with Colors by the way but we have a
color for this pen there's a height uh
there's a kind of pen it also has a
brand I'm not sure which company pen it
is it doesn't matter so there are some
properties for the pen right and the
same way if we talk about this uh this
remote okay this is this has some
properties height color uh the number of
buttons so this is what a remote knows
and also a remote does something example
I can on my AC by pressing some button
so it has a behavior as well so
basically every object knows something
every object does something and that's
what we are going to create in Java as
well now whatever project you are making
you will be having uh different objects
now specific to Java from now it's it's
also about thinking okay so it's not
just about coding something even when
you start making something in your mind
you have to treat everything as an
object example let's say if you want to
add two numbers the first thing you
should which should come to your mind is
okay I need an object which can add two
numbers
getting a point right everything you
have to think in object way so if you
come back to programming if you look at
this example of course we don't have an
object here in this code but you have to
remember whatever I want to do you have
to do with the help of object so what we
have this discussed till now is there's
a concept of object oriented programming
so basically we have certain things here
we have a concept of object and this
object will have a property and this
will have Behavior so every object will
have a property and they also have a
behavior the properties can have
multiple properties and multiple
behaviors example let's say if I as a
human if I'm an object I know something
I know a lot of things I know how to
talk how to walk how to dance how to uh
type code right and I behave based on
what I know so I can dance because I
know how to dance so that's your
property but you know how to dance
that's a behavior when you're dancing
when you're talking when you're walking
right so I know my age as well I know a
lot of different so whatever I know here
is properties what I what I do is
behaviors okay but how do we create
objects so in in Java if you want to
create an object we have to first create
a class okay now why we need object and
Clause concept so first of all we have
talked about object everything has to be
done with the help of object in real
life we can't do anything without
objects so that's how it works so in
Java as well if you want to do something
you have to create an object
but how will you get an object and who
creates this object
so let's talk about it now if we talk
about the concept of object who creates
object in real world example let's say
if you talk about this table when I'm
with I have my systems now this table is
created by a carpenter okay so when you
go to a carpenter by saying Hey I want a
table Carpenter will say okay uh I will
give you a table but tell me the exact
dimensions okay uh maybe take the
carpenter the actual guy who is making
this table he is very technical so we
have to explain in technical details and
that's why we have sample sign between
who says okay you give me the details
okay I will forward it to the carpenter
so basically you give the details to the
to that person 30 percent and then that
third person gives a detail to the
carpenter because Carpenter understands
One technical details and you understand
on the later terms I can say hey I want
a table where I can keep my computer
where I can keep my monitors my keyboard
mouse mobile phone and all the all the
different things which I have on the on
the table here
so that person in the middle person will
explain everything to a technique or the
carpenter okay that's the dimension a
person wants uh this is the height which
I want based on my height I want this
table to be and uh so all the details
right so got the point so how do you
give that design so as a novel person
you give a design in a particular way
and in programming you can give that
design in a class file so you have to
create a class file which will act as a
blueprint for the carpenter or for the
for the for the sum for someone who can
create object for you in Java now who
creates objects in Java it is your jvm
again what is jvm what is JR will have a
digital discussion there but at this
point understand this we have a jvm who
will say okay it's my job to get the
object but you give me a blueprint okay
so basically you create a class file now
this class file gets compiled to create
a byte code now that byte code goes to
the jvm and that's where you get the
object
okay so in the last video we have talked
about what are classes and object right
and we have seen the theory of it in
this video let's try to create a class
and we'll also create an object of it
now first of all where do we get a class
and what class I want to create as I
mentioned before in Java what you want
to do you have to do that inside a class
so in that class you'll be having
methods you'll be having variables how
do we do that that will say in some time
but the first question is where we have
to create a class now the class can be
created in the same file so example in
demo.java we already have our class
right
we have a demo class and here with this
class I can create another class here
and we can surely do that so what I can
do is I can create a class here and I
will name this class as calculator now
basically imagine what I want to do here
is I just want to add two numbers so
even if you want to add two numbers
we'll do that with the help of a class
now what if you don't use a class and
normally how you do it so let's try that
first I want to just add two numbers and
I will remove this extra comments from
here now how do we add two numbers it's
very simple you use variables let's say
int num1 comma num2 so we got two
variables here and then we have to give
them some value as well so I can just
come back here I can give them values I
can say num1 is equal to 4. and num2 is
equal to 5 simple numbers right in fact
you know what works well is to have this
in two different lines again coding
standards if you have variables on
different lines it is much much easier
to read and much easier to maintain the
code as well now once you have these two
variables if I want to add these two and
of course when you add these two numbers
you will get the output you will get the
result
save results somewhere so I will say int
result equal to num1 Plus
num2 so you can see we got these two
values and then we are adding them
okay so in result we got the value and
of course you can print this value so
you can simply come back here and you
can say result print result that
perfectly works now the twist here is I
don't want to add these two values here
of course this code will work I just
want to see if this works before we do
something
I will say compile and run so you can
see we got nine but I don't want to add
these two values here so how do we
represent that in a separate class uh
it's something like let's say if you
want to call someone YouTube you will
not manufacture a phone by yourself you
will just buy the phone now this phone
company they will Design the phone they
will make the phone example if you talk
about iPhone in let's say you know
nowadays they don't mention that on the
back of the phone but initial days they
used to say uh okay let's talk about
some other phone first you know most of
the phones doesn't matter how costly it
is uh so they it is mentioned it is
where it is made uh in the previous the
previous uh manufacturing how was China
so most of the phone was having made in
China right uh but then if you think
about Apple they are smart in this case
they say designed in California and
assembled in China so even they believe
designing is more important than
assembling and that's what you have to
do here because manufacturing of your
object which you do here will be done by
jvm what we are concerned about is
designing of it so when you design it
you can just put come back here and you
can say class and I will just name it as
a calculator
I can just open the curly packets and
close
so this is basically where you will
design your stuff you will put your
things example if you talk about
calculator and if I mentioned that
before every object will have two things
properties and methods you will do that
in this particular calculator
now what I want to do is I want to add
these two values right
so if you want to add that's a behavior
right that's an action action will be
done with the help of methods so here I
will say public so how do we get a
method so we have to specify the access
to it which is public I want this to be
called from anywhere else and I want
this to return me a value so once that
is called it will perform some operation
and it will give back the value so I
will say ain't that's the written type
so whatever it returns we have to
specify the written type of it as I
mentioned before Java is a statically
typed language which means you have to
specify
for all the data whatever data you're
working with when you create a variable
you have to mention whatever variable
you want to create when you return you
have to mention what type of data you're
going to return so that's end and what
could be My Method name so method will
also have a name so here I will say the
method name is ADD and this ad will
perform an operation now at this point
you can see I'm not passing any value
I'm just saying add and when it calls I
just want to print in ad I just want to
see if this get really get called okay
so at this point I don't want to add I
just want to see if this is getting
called and also we are returning a value
right and that's what the errors it says
it says the method must return a result
of type int okay uh so I have to return
something so irrespective what type of
calculus I'm doing I have to return
something
's a return so that's how you've written
the value you have to use a written
keyword and then you will give uh any
value it doesn't matter any integer
value so I'm at this point I'm giving 0
because we are not concerned about this
value but the question is how do I call
this ad okay so this is basically a plus
a class will have methods a class can
also have variables what if you want to
get variables here it's very easy just
outside the method and inside the class
you can just mention the variables at
this point I just want to get a variable
a just to show you that how do we get a
variable we are not going to use this a
anymore but let's let's keep it there
so in a class this is how you design
your class you do you put two things
there you put your variable and you put
the method the variable name is a the
method name is ADD makes sense right and
here we are just adding these two values
putting that into result but we are not
going to use this anyway so we'll sub
comment this part and comment see the
ultimate AIM now is how do we call that
add method
that's tricky so in order to call the
add method
can we directly do that can we just
directly call a method like this so
that's a method right now if you're
coming from some other languages it
might be supported where you can simply
mention the method name and it will work
at this point you can see it is not
working we are we are getting the error
itself in fact there are two type of way
you can check the address you can
directly see in the IDE if you're using
it otherwise you can just compile the
code to see the exact error it says
cannot find symbol okay that's weird the
ad method is there right but it still
says cannot find symbol you know why
because if you can see in the error
itself it mentions that the symbol add
which is a method it's not it cannot
find that method in the location demo
oh okay so when you call AD is not able
to find that in the same class
but it's not in the same class right in
a different class
how do I mention that hey you know this
ad is it belongs to a different class
for that basically what it says is the
design is not enough basically what you
need is also the object example let's
say if someone comes in the world by
saying hey no we have this amazing idea
and we wanted to buy this idea nobody
will buy the ideas why do you buy the
devices no one will give you a uh I mean
you will not buy a phone
odd idea which using which you can call
someone it says you know this device can
call but then you don't have a device to
call uh so basically we need an object a
physical object in the world of
programming we need a virtual object
so for this class which is a design I
want the object the instance which I can
use
how do I do that how do I create the
instance now for that you have to come
back here and you have to say Hey you
know I have a calculator class and I
want to create an object of it so
basically imagine calculator as a type
example if you want to get a variable
like num1 you specify a type right which
is int so here as well imagine Calcutt
is a type and then you are creating an a
reference of it let's say calc
they are also variable the calc is also
variable the difference between these
two is this num1 and num2 they are
called primitive values or primitive
variables is because ain't and all those
type uh flow double they are primitive
this calc is of type calculator so we we
normally call them as a reference
variable
so that's done uh let's say we have this
calc calculated calc and then using this
calc I can say calc dot add
but still it will not work the reason we
are just creating a reference we are not
getting an object yet
okay how do we get an object
now first of all who creates an object
and every time you get an object in this
world you know we are talking about
carbon neutral we are talking about how
can we reduce the e-fest in the same way
uh every time you buy a new phone
basically you are creating an e-vest
because when when you buy a phone the
companies are manufacturing new phones
okay so basically you are increasing the
E-Waste in the same way in jvm as well
every time you get the object it will
consume some space
okay how do we do that first how do we
create an object how do we consume that
space now for that you have when you
want to consume the space you will
simply say Hey you know I want to create
a new device so you have to say new
but whatever device it will ask you in
that case you have to mention I want to
create a object of type calculator and
you have to also give the round brackets
now this is how you create the object
okay this is how you get an object of
course we'll talk more about this uh how
do we I mean what's the difference
between this line and this part but at
this point just to keep it simple
this is how you create the object first
you mention the class name then you
mention the reference variable name or
variable name using which you can access
the methods of calculator and then you
send new keyword that's how you consume
this space but how much space you need
what what are the variables you have to
initialize that can be done with the
help of this thing now it has a special
method in Java called Constructor but
what is Constructor we'll talk about
that later how it is different from
methods we'll discuss that in detail
later
but at this point with this line we got
the object and once you got the object
you can simply call the add method your
job is done
but will it really work let's try so
what I can do is I can just clear this
and I can go back here compile
and run you can see we got in ad
basically you were able to call in ad
that's great
okay but if you can see
this add method actually returns a value
so don't you think we should accept the
value as well if someone gives you
something you have to accept it as well
so here I can say end result so whatever
it returns I will put that into this
result variable and I will just print it
and let's see what happens so compile
run oh it works you can see it says in
add and we are also printing the value
of result which is zero y 0 is because
we are returning 0 but what if you
return something else maybe I'm going to
return based on the values which I have
here
oh that means here
I don't want to print something what I
want to do is I want to create a
variable called as let's say R is equal
to I want to add num1 plus num2 and then
whatever addition I'm getting I will
just return the value now it will make
much more sense so I didn't show if
you're doing 0 I should I should be able
to return the value so now 1 plus num2
should be assigned to R and I want to
return the r but the only problem is I
mean let me compile this code to see
what happens compile oh we got errors
and you know I love errors because
errors will teach you a lot of things it
says num1 and num2 cannot find which
location in calculator and you have to
mention hey you know I was actually
talking about number num2 which belongs
to demo in fact the main method so what
you can actually do is uh can we when
you're calling ad can we just pass these
two values something like this four and
five right and then since you are
passing those values example let's say
if I ask you hey you know add two
numbers the obvious question from your
side would be what numbers give me the
values first right so I will say Okay
add 15 plus 20 then you will say okay
that's 35. so that means I have to pass
a value so when I call you to add values
I have to I have to give you the values
and then of course you have to accept
those values it's not like I am giving
you the values and you are not listening
to me so I have to accept those values I
will say N1 comma N2 different variable
names
I have to give int
and then here instead of adding num1 and
num2 I will add num n 1 and 2. the
variable name can be number random two
as well just to just to differentiate
between these two I'm just giving
different different variable names
so the idea here is whatever value you
are passing 4 and 5 will be assigned to
this N1 and N2 and that's how you can
pass the value
make sense right and anything else
let's try this let's see if this works I
will just clear this and
compile
okay I've done comparison two times my
bad so you can see we got nine so it is
working basically whatever value you're
passing it is getting passed here
but there's one more thing
when you have those values in a variable
why you have to mention numbers here we
are hard putting values not a good idea
so what you can do is instead of writing
4 here we can write number one and
instead of writing
5 here I can write num2
simple stuff so whatever value you have
here you are passing it here and then
that gets assigned to num1 and N2 and
then you're adding the value
let's try
compile
run it works
so what we have done is we have created
the class how to get a class it's very
simple you say class and you mention the
class name which is calculator and then
in that class you can create variables
you can create methods this is how you
specify what object knows right
variables data and what object does an
object can add two values
now how do we use this class basically
you have to create an object of it so as
you can see this is how you create the
object you say Hey you know jvm I want a
new object you see you you use a new
keyword there and then jvm says okay I
will give you the object but also tell
me design
and this is how you mentioned the design
you say calculator now this will give
you a new object of what type calculator
so you're assigning that to a variable
called calc of type calculator example
when you say 5 that's an integer type
that's why you say int num2
this is an object of calculator type so
you will assign that to calc which is a
calculator type variable now once you
got the object reference here you can
just use that reference and you can call
the add method by passing two values
return the value and print
simple stuff that's what we have done in
this video so till this point we have
seen some programming thing and we were
able to execute them we have talked
about classes variable methods and
object relation as well now it's time to
actually see what is happening behind
the scene because if you understand what
is happening behind the scene then the
further cooling will make sense right so
every time I introduce A New Concept we
can actually relate what is happening
behind the scene now to understand that
let's focus on some keywords okay if you
remember we when we started this videos
at the start of the video I mentioned
that to compile the Java code you need a
tool right in fact you have to do setup
as well and that tool is your jdk now
jdk here stands for Java development kit
maybe I can just write it here so
basically why do we need it why do we
need a development kit see the thing is
when you as a programmer when you type a
code you have to convert that code into
byte code because ultimately the what
runs on the machine is your is a
bytecode so of course you cannot type A
bytecode I mean you can don't try it but
the idea is you will type the Java code
you will compile it and it will convert
into bytecode which will run on a
machine but which machine now for that
we have one more term here which is
called a jvm now basically jvm stands
for Java virtual machine
so basically this is your machine which
runs the code so of course you have to
compile the code with the help of jdk
and you have to run the code on jvm now
apart from this there is some more
things in the picture so what happens is
when you want to run your code so what
code I'm talking about I'm talking about
the byte code here so assuming that you
have already compiled and you have a
byte code with you you need to get a
space okay so let's say this
is your space where you are going to run
your code and this space is basically
your j v m now this is where you
actually execute the code now why it is
called jvm is because we have a machine
and to make deep Java platform
independent we went for a virtual layer
on top of it so it doesn't matter on
which machine you have your jvm it will
work the idea is to have jvm on every
machine now jvm is going to run your
code and behind the scene computer will
convert that into its own away and it
will run
so basically you need a jvm to run your
code but then what happens is for your
code let's say this is your file here if
this is your file which you want to
execute most of the time your code is
dependent on some external file not your
files which you have created maybe you
have created five files apart from the
code which you have written you have
used some inbuilt classes some inbuil
libraries and that's where we need some
extra things here so maybe we need some
extra files from which you are going to
use in your code okay now question is
where you will find all this code and
that's where we have one extra layer
here
on top of it which is your JRE now JRE
stands for Java runtime environment so
basically we have a concept of JRE which
is Java runtime environment now in this
Jr you'll be having all the extra files
you need extra classes in the classes it
also checks your byte code basically it
validates your byte code or maybe you
want to load a class so here GRE will
help you but ultimately your code will
run on jvm so jvm is very important
because that's where that's where your
code runs but even to run your code you
need some extra files and that's what
GRE will provide you and the name itself
says right Java runtime environment so
it's an environment where you can run
your code and the beauty is jvm is a
part of GRE so you can't simply say hey
we don't need GRE we need if we don't
have a GRE you don't have a jvm right so
basically every time you when you say
you have Java in your machine to run the
code you actually have Jr with it so you
have a JRE and inside that you have a
jvm but then as a developer you install
jdk right right now jdk acts like a
upper layer so every time you install
jdk you also get these two as well so
the the top layer here is your
jdk so jdk when you install jdk you will
get the updated JRE and also you will
get the updated jvm but by default on a
client machine you will find jrd and jvm
which will have extra files and which
will have where you can run the code in
fact you might have seen this sometime
when you when you install some software
it will say Hey you know in this machine
I'm not able to find.net framework or
I'm not able to find Java it's because
the software will be running on those
particular softwares I mean the
application will run on dotnet platform
or on Java of course there are other
platforms as well just to give an
example we have dotnet Java and that's
why you know you'll have you install
extra softwares the same thing if you
don't have the updated version of GRE
and if you try to run some Advanced
software it might not work and that's
why you know sometime on Windows uh it
says Java is getting updated for the
same reason because to support extra the
new softwares so this is basically your
jvm Jr and jdk so jdk will have
everything JRE and jvm and in jvm you
execute the thing now in the next video
we'll try to expand more on jvm so in
the previous video we were able to work
with a calculator and basically we're
adding we were able to add two numbers
right so what we did is in this
calculator we have created this method
called add and then we have accepted two
parameters and then we were able to add
them and we were able to return the
value now of course the place from where
you are calling this method uh returns a
value and that's what you're saving in
result and you are putting it that now
in this video let's try to understand
more about methods of course in the
entire course we will be using different
types of methods we'll explain how this
method method is behaving this way but
at this point let's understand about
methods more so what I will do is just
to simplify this I will remove this
class and I will also remove the entire
section from here now if you can see C
by default even if you have one class
here which is demo by default we have
one method which is main now main is a
method which is a start of execution so
it defines hey this is where we have to
start the execution so by default we we
are anyway using a method right but then
if you understand the actual development
of any kind of product it can be a car
or a mobile phone or a software now we
normally create modules example if we
talk about a car we have different
modules there right we have wheels we
have uh doors we have Bonnet we have
engine right so all these things come
together to to form a car in the same
way if you talk about a big software we
break down this offer into small parts
and we try to create those as a
component now in Java we can create
components with the help of classes
right so we can say hey if you want to
build a car maybe let's create a class
called Wheels let's get a class called
uh engine let's create a class called
seeds right so all these things comes
together
now every class here is which whatever
class you work with let's say wheel
Class A Wheel class will also have its
own behavior right so we'll have some
data we have some Behavior so here if
you talk about Behavior if you want to
Define hey this is how the wheel will
move this is how the uh the engine will
work now all those things comes under a
behavior and we do that with the help of
methods just to simplify this let's say
I create a class and I will link this
class as ABC it can be any component or
maybe I can I can say this is a computer
of course even a computer is made up of
multiple components but just to simplify
things let's say we have a computer it's
a class okay and then in this class I
can Define the behavior what a computer
can do a computer can run games a
computer can play music so I can say hey
I want this computer to me to play music
in fact in my childhood this is what we
used to do when we used to get computer
to access uh I was around I was in my
11th standard when I got full-fledged
use of computers and at that point
uh when I say I I got to use computer
what the thing I will do of course we
can use paint we can use Ms docs which
is the word or we can use some amazing
media player to play music right so here
let me say uh this computer can play
music okay now how do we Define that's a
behavior we do that with the help of a
round bracket and then this play music
will do something so we have to open the
brackets and close this is where you
will Define what is a behavior of this
particular method
and every method we also have to specify
what type of access you're giving of
course we'll talk about access later but
at this point let's make it public I
just want it to be accessed from
anywhere and also a method will do
something right so that's what we are
doing here now this method will do
something and it will give you something
in return example let's say if I ask
someone here so let's say if I have
Hershey and if I say hey I want a pen
now at this point as a external method
I'm asking her to give me the pen right
so what I'm expecting from hush a pen
right maybe I want to just get some
information maybe I can just ask hush
hey can you just call someone to send
this information
so at this point if I am asking her to
call someone I'm not expecting anything
in return
so what I'm doing is when I say I don't
want anything in return is wider so of
course your method can give you back
something you can say a method can give
you uh integer value a method can give
you a pen as well so this method which
is play music is not giving you anything
it's just performing some operation
now of course we can write multiple
lines of code here to play the music but
just to keep it simple I will say music
playing or playing music it doesn't
matter so we are just writing this
statement here now this is my method
that's how you define the behavior we
can have some extra methods as well I
can say public and this is get me
a pen
okay this is a method name I have and
this method will give me something so I
will say turn so what it will return so
let's say I want I want to get a pen but
at this point we don't know how to get a
pen right so let's say I will I will
return a five value now if we talk about
this five this five is a number right or
maybe I can just return pen now if you
can see this pen is a string now string
is a special type in Java which is a
combination of different characters so
we have to put that in double quotes now
we are returning a pen so here we can't
say void because when you say y it means
you're not expecting anything into in
return but here we are doing that we are
returning a pen in a string format so we
have to say I am returning a string so
whatever type you written here you have
to mention that we're going to type here
makes sense right so basically we got
two methods and then it is also possible
that when I say hey get me a pen
hush will say okay I will get you a pen
but you have to give me money first of
course right no one will give you
something for free so I have to provide
the money here so if you ask a method to
do something it comes under your design
how you want to design it do you want
your methods to exp accept something
from you or what type of data you want
to return so here I'm saying this get me
pen will it will get some integer value
so let's say I'm passing 10. so normally
one or not 10 but available which is num
I will say cost
so basically you have to pass a number
let's say 10 so one pen will cost to 10
Rupees and then if you want to call this
get me a pen you have to pass the value
as well
make sense right now we have two methods
how do we create how do we call them so
from this main which is in some other
class if you want to access this method
the first thing you have to do is you
have to create an object of a computer
as I mentioned before every time you
have a class which is just an idea right
class is a blueprint an idea and if you
really want to use those ideas you
really need an object how can we use
something without the object right even
if you want to call someone you need a
phone with you a physical phone not a
virtual concept which using which you
can call someone okay so let's say here
we have to get object of computer so
we'll say computer comp of course you
can give any any reference name here we
can also say obj which is very common so
you can say computer object equal to new
computer
and that's how you create the object
right so this is a line normally we use
to create object but only these two
things are actually getting the object
here this is a reference variable and
now using this obj I can actually call
both the methods I can call uh play
music
so let's try with play music only and
let me clear this screen here
so we'll say Java C
demo.java and you can see we got the the
comparison done let's run this code I
will say Java space demo it says music
playing so this is working uh can I call
get me a pen let's try so I can say obj
dot get me a pen but if you can see get
me a pen is asking you to pass a integer
value so let me I will pass 10 here
and I can just run this
the only thing is if you say get me a
pen it returns a value which is a string
format that also means that when you
call get me a pen here it will return
you something it will give you something
so I will put that into a string Str
so I can say string Str of course you
can use any variable name but that's a
string we are not using integer double
here we are working with string and of
course we'll have a separate session or
separate video on string at that point
we'll understand that here what I will
do is I will just try to print this Str
just to see what it is printing I hope
it will print a pen and yeah that's what
we got we got music playing and we got
pen
cool now there's one more thing here
which is what if it in this cost so
let's say you're passing 10 that works
but then what if someone is passing
letter two now of course we'll not get
any pen for two rupees right of course
it at this point it will work because we
are not doing any any checking I don't
want to return a pen when the cost is 2.
so how do we do that I want the minimum
value for this cost to be let's say 10
Rupees in that case you can remember we
have talked about if else so we can
actually use if else here so we can say
if the cost is less than or the cost is
greater than equal to 10
then return pen otherwise don't return
pen right it's very simple if your if
the cost is more than 10 or equal to 10
then you have to return pen otherwise
don't return pen someone is calling this
method you have to return something in
this case you have to write else
return and you can say return nothing
you know the weird thing is at the time
of recording there is a phone called
Nothing phone so basically what you're
returning here or nothing phone ignore
my poor jokes but yeah so what that's
what you're doing here you are returning
nothing and you can see I am passing 2
here and of course the consumer will be
false it should return nothing let's try
compile run and you can see we got
nothing
okay so this is working and this is what
we wanted
you can do one more thing you can simply
say you don't even have to mention the
else keyword you can simply say return
nothing but then you will say it will
execute return nothing anyway right the
thing is the moment your code sees
return pen here it will just jump out of
this method it will not execute the
further statement what I'm saying is if
the value let's say is 12 not 2 12 of
course this will pass the condition and
then once it is true it will execute
return pen the moment you set return
keyword in a function or a method it
will return the value it will just go
back it will stop the execution
and that's what we will be getting here
so if I compile this code and run you
can see it says pen it's not printing
nothing but yes if the value is 2 in
that case this condition will be false
this one will be false and it will not
execute the return statement of if it
was execute return nothing and that's
why it will Point nothing now if you can
observe there is one difference between
these two methods here if you can see we
have get me a pen and we have Main
the differences of static keyword and we
have not talked about static gate so let
me talk more about the methods and this
is important for the further Concepts
and very interesting so let's say again
let's go back to our calculator to get
some more understanding of it so I will
say it's not a computer it's a
calculator of course in a computerizable
we can do calculations but just to keep
it simple let's go with calculator so we
got this class here and let me also get
the object here and there is no
compulsion that a class should have the
variables and methods we can keep it
empty as well that perfectly works so
you can see we got calculator obj equal
to new calculator and then here I want
to let's say add two numbers I know I
know you'll be saying we have done that
before but let me just do that once more
and you'll understand what I'm doing
so you can see I'm saying public end I
want to add two numbers why int is
because I'm expecting some written value
and it will accept two values one is N1
and 1 is N2 and here I want to return
the value of course you can simply
return the addition of it so you have a
choice you can create a separate
variable uh what I'm saying is you can
create a variable like result and you
can say N1 plus N2 and here you can say
return
result this works uh you know we can
actually do a shortcut here if you look
at this variable result is only used
once we have assigned the value and then
we are returning a value so can we just
do this can we just say return N1 plus
N2 we don't have to create a new
variable
okay so you will get used to it once you
start making progress you will get used
to it so you can see we got a calculator
which can add two values and then
returning the addition of that this
perfectly works right so what I will do
here is I will come back to my code I
will say obj dot I can call this add
method which will take two values three
and let's say four so it will return a
value right so I will say int R1 so int
R1 is equal to this addition and I can
actually print this value so let's
compile this code uh not running
directly first you have to compile the
code and run you can see we got seven
this works so what we are doing is we
are calling add by passing two values
which is three and four what if you want
to add three values that would be tricky
so of course you will say I mean think
about this if you want to add three
values the first thing comes to your
mind is it's easy we can change this
particular method which accepts three
values right and of course you have to
pass three values because if you pass
only two values uh your compiler will
feel bad compiler will say Hey you know
uh you have a method which accepts three
values and you're passing only two
values not fair okay so you will say
okay I will pass to I will pass three
values and that perfectly works I will
just compile this code and run and you
can you can see we got seven oh we got
seven because we are still adding N1
plus N2 we are not adding N3 so let's
compile and run you can see we got 12
this is working but there's only one
little problem here not a little problem
actually big problem what if now you
want to add two numbers sometimes you
want to add three numbers sometimes you
want to add two numbers again it will
not work
your compiler will say Hey you know we
are expecting three values and you're
passing only two now unfair right okay
how do we solve this problem maybe if
there is one solution which comes to my
mind is what if you can just create
another method which can accept two
values I can say public int add one
which will accept int N1 comma int and 2
and this will return N1 plus N2 now this
perfectly works the only thing you have
to do is you have to remember what
method you have to call because add one
adds two numbers and add as three
numbers of course you can make it more
effective by naming the method name as
add two numbers add three numbers okay
we we were able to solve that but the
problem is the moment you have more
methods you have to maintain the
documentation for those methods and also
it's very difficult to remember the
method names add method looks much
better right instead of adding two
numbers adding three numbers so can we
do this can we have the same method name
that can solve our problem like this of
course I have two methods but then but
they have the same names the only thing
which is changing is the parameters if
you can see this ad take three
parameters this ad takes two parameters
so that's right we can have the method
name of with the same name the only
requirement is they should have
different parameters example if you make
it same parameter here again it will not
work it will say it's a duplicate method
add we can't do that so basically we
need to have different parameters and
it's not like they have to be in numbers
they can also be of a type what I'm
saying is what if you want to have the
same method I will I can just reuse my
code here and instead of int I can also
have a double value
so I can say double N1 and N2 and I can
just simply return the only thing is
when you double when you have double and
int you return with double because
double plus eight will give you double
that's it so it's not just about the
number of parameters it's also about the
type of parameters so you can have
different number of parameters or you
can have same number of parameters but
of different type now this concept in
Java is called method over loading
because you have two methods with the
same name in fact three methods here
with the same name what is different is
parameters it is called method over
loading now likewise we also have one
more concept is called method overriding
where you also have the same name but
things work differently there it's more
about inheritance and thing at this
point we are focusing only on the
overloading part how about this see
every method will have a name and
parameters what if you have the same
parameter but different written type
even that will not work it has to be
with the parameter itself this return
doesn't matter what matters is the name
and the type now let's try to understand
what is there inside the jvm so what I
will do is I will just go back here and
let me draw a bigger jvm because that's
what you're focusing now if you talk
about the outer box for this that's your
jrd outer box for that is your jdk but
let's focus on jvm here and also name it
j b m now what we normally do here is
this is where you execute the code right
now question arise how exactly we are
going to execute the code of course
there is something called a runtime or
the runner which will do that here we'll
focus more on the memory level what
happens on when you create a variable
when you store a variable in your memory
or inside jvm memory we have we can
categorize into two parts the first one
is this this is how it looks like of
course I want you to guess so basically
this is a area where you can store or
your data and that has a feature which
is last in first out example let's say
if you send data which is five six so
let's say if you send data five six
seven now the first value which entered
was five second value is six third value
is seven now when you try to get the
value you will get 7 first because that
is last in first out now this is called
stack so basically you have a memory
which is called stack memory now apart
from this memory you have one more which
is you call as Heap now on purpose I am
drawing this type of image where it
represents that it expands right so this
memory here is your hip so basically we
have a stack and we have a heap memory
so in the stack you store data in a
different sequence and in Heap you have
a open space now before we jump into
this memory how it works let's focus
more on this code okay remember when we
talked about calculator and then we have
talked about these two variables now
here when you talk about this N1 and N2
variable the variable but they are local
variables okay just to reiterate those
are called local variables now what do
you mean by local and what are different
type of variables we have so if I create
a variable here let's say num now in a
calculator we have a num variable and
then in a method like add we have N1 and
N2 that's right the N1 and 2 are part of
add method now here the N1 and N2 become
your local variable and num here becomes
your instance variable that's right the
word is instance now what happens is the
moment you create this the moment you
have main now the beauty is every method
will have its own stack that's right
it's not just one stack every method
will have its own stack and if you can
see in this code we have two methods
right so of course you will be having
two stack what I will do is I will just
redraw this tag to accommodate more data
so what I will do is I will just zoom it
a bit so let's say we have a stack here
okay this is your first stack and a
stack will have two section okay and
basically it will have two columns and
multiple rows depend upon how much data
you want to introduce now if we talk
about this main this particular stack is
actually your main stack so I can say
this is my main stack now in this stack
you will be having your data so what
data I'm talking about if you go to the
main method if you can see we have a
variable a okay now that's also a local
variable okay so I can say hey I have a
variable which is called a here so I'm
just reading a there now what's a value
at this point there is no value for a so
I will just ignore that part maybe let's
not even mention that once we talk about
string then it will make much more sense
let's start with the variable here maybe
I can create some more variable just to
understand so I will say int data is
equal to 10. so what I'm doing is I'm
creating a variable which is a local
variable again inside the main method
and you can see we can say this is my
data variable and the value for that is
and straightforward we can assign the
value 10 because that's the value so
basically your stack will have a key and
a value a key would be name of a
variable and value will be 10 the value
itself now coming back to R1 here okay
let's ignore this obj as of now and mind
you this obj is also available so it was
a part of this tag so data obj R1 they
all are variable
so it says Okay I want to have R1 as
well so I got R1 variable but what is a
value for R1
and that's where it will basically call
the add method okay so it will call the
add method but we don't have our ad
method in the memory as of now right so
if you see in this memory you know where
we have ADD so basically what we have to
do is it will create a new stack out of
it so we got another stack and the name
for this stack would be add and of
course it will have two sections and
multiple rows so two column multiple
rows now if you see in this particular
ad we have two variables N1 and two so
of course we have to define those two
variables N1 and N2 what are the values
for these two variables we are passing
them right three and four the moment you
pass these two values it will go to N1
and N2 it will assign those values so
the value for n 1 is 3 the value for N2
is 4 okay that's good and then you are
executing add method so in add method
what we are doing is we are just adding
those two values uh three and four which
is seven it will return the value
whatever value you have returned it will
return the value with this particular
method to R1 so that's right we got R1
as 7. I hope this makes sense
cool uh so we have done the changes
there as well so R1 is now seven
what else
now what happens to this method ad we
have called it right so there is a
special method area where you have a
different stack of calling methods so
when main call add add will execute
First Once ad is over it will be gone at
this point let's not talk about the
function calling let's only focus on the
data areas so basically this is what we
do there right but what happens with the
object here now that's tricky and what
happens to this num variable where do we
put in a variable in the add stack in
the main stack no if you can see num is
not a part of add is not a part of main
the beaut is you can actually print the
value of or you can use the value of you
can use a variable num inside a method I
can actually print the value of num here
so maybe I can set the value as let's
say 5 and I can actually use this num
inside a method see using a particular
variable and the declaring the variable
inside a method are two different things
at this point we are using it we are not
declaring it inside a method N1 and N2
they are declared inside the add method
but not num and that's why if you if I
if I can show you if I compile and run
it still works you can see we got num
which is five so we can use it but the
question is where it resides not does it
resides in add stack or main stack the
the answer is and that's where we have a
heap memory there right now inside the
Heap memory what happens is just focus
on the line number 20 here on line
number 20 what we're doing is we are
saying calculator obj now if remember we
have talked about this multiple times
this obj is not an object now people
coming from C plus plus you might be
having this urge of calling obj's object
but no that's a reference variable but
that's a variable right now this
variable where it will get created it
was declared inside main so of course we
have to say o b j here
but the question is what will be the
value
now for that you have to understand what
is happening here now when you say new
calculator it will simply create a new
object where it will create the object
inside the Heap memory this is where you
will get your object
and inside this object you will be
having two things actually so let me
just draw the first object quite bigger
and later on we can draw it small so
this is your first object the object
will have two sections the first section
will have all the variables all the
instance variable not local variable you
know why because local variables are
part of a stack so the part of the stack
not of Heap but if you talk about the
instance variable like we have num here
they are part of the Heap memory and
this is where you can say variable name
or num the value for that is let's say
five we have assigned five right
and then this particular object will
also have methods and this in this Heap
we are saying this is an object of
calculator it will also have the method
declaration so it will have ADD method
but then it is only have the definition
of it the actual area which ad will
consume will be of Stack okay if that
makes sense of course we can have extra
methods as well at this point we only
have one now this particular object will
also have its own address let's say the
address is one zero one of course right
when you store the data it has to get
some address now that's one zero one of
course it will be a complex address at
this point I just want to keep it simple
one zero one now this one zero one will
be stored in the stack so every time
when you say obj dot add the actual
execution starts from from stack itself
you say okay someone is trying to call
example if you talk about line number 21
here we are saying obj dot add that
means we are using obj object to call
the admit method but it belongs to
orbital object right which is the object
here
so it will simply use this particular
address
it will jump to the object and it will
call the add method so can we say there
is a link between stack and hip yes
because of the address right and that's
why you can use this object multiple
times and that's important in future we
are going to talk about Anonymous object
as well and we'll discuss why this link
is important and it will make much more
sense at this point just imagine there's
a link every time you say open J dot add
you are going from Main looking at the
stack then you are jumping towards the
Heap to look for the object I hope that
makes sense the good thing is we can
actually create multiple objects I can
just copy this line or maybe I can say
code reuse and I can create another
reference which is obj1 and we got a new
object here that's right in total we got
two calculator objects so with this
change is what we are getting is we will
be getting a new object here let's say
the address is 105 and it will have the
method it will have it will also have
num variable and the value will be 5 of
course you can change it and you can
have ADD method okay this is num okay
not n but imagine that's num and you'll
be having obj one here because in main
we have one more Declaration of obj1 it
will have the address 105 and you can
imagine there's a link between stack and
Heap okay now when I say these two
different objects have two different
values or two different num variable but
they have the same values of now right
example if I come back here you know
what I will do just to simplify this
thing more I will just comment all the
other print statements
to see only one output so here what I
want to do is I want to print obj dot
that's right if you want to even use the
variable the instance variable you have
to use the object name which is obj1 in
fact the first object is obj the second
object is obj one dot num so you can see
we got two objects and we are printing
the value of it each num value and if I
run this code you can see we got five
and five you know why because that's the
value you have assigned now my question
to you is before printing the value now
if I say obj dot num is equal to eight
you can see I'm changing the value of
only one object what do you think will
it reflect on both the object or only
one object let's try so when I say
compile
and as one you can see it is impacting
only one object it's because there are
two different objects right example
let's say if I have this phone this is
Samsung and let's say I have the exact
other Samsung phone
and one of it so let's say if the glass
of one phone is is broken will it affect
the other other phone of course not
there are individual phones and damaging
one phone will not affect the other
phone
so that's the important point to
remember here so yeah that's it about
the data area so they have different
areas we have stack and Heap in this
video we'll talk about
adding now first of all why do we need
an array so in this video we'll talk
about the need of an array if we talk
about a variable so normally when you
create a variable it's very simple right
in a variable you can store a value now
this can be of type integers flow double
uh string doesn't matter you have a
variable and you can store values in
that example let's say if you talk about
let's say int variables so how do we do
that how do we work with into variable
so we say int I is equal to 5. so what
happens is you have a variable here
which is I which has a value of 5. what
if you have one more variable here which
is let's say J and it has a value which
is six maybe one more you have end K is
equal to seven so you can see we have
three variables here and you have three
values now first of all why do we need
three variables here is because we have
three values what if you can save all
these three values in one variable now
why I'm doing that is because the moment
you have more variables you have to work
with multiple variables you have to
remember those variable names uh you
have to document them instead of that if
you can save that in one particular
variable it will be easier for you to
maintain the data and also it's not just
three values you may you might have ten
values you might have 20 values you
might have 100 values you don't want to
create 100 variables right so for that
we can use a concept called array here
now how it works we can create a simple
variable let's say num and in this num
instead of storing one value I can store
three values so let let's say if I have
five six and seven I'm storing these
three values of course we can put comma
to separate them and then we can put
them in a curly brackets to represent
that this is a bunch of values I want to
store and I want to assign that to a
variable num now being a simple integer
variable it will not work you cannot
simply take a integer variable by
assigning four values reason the moment
you create a variable here it occupies
some space now if you come back to this
particular variable here of course this
will occupy some space now in that
limited space you can't store multiple
values right you have to mention
somewhere hey this particular num here
is not a normal variable it's a a
variable which can hold multiple values
and with the way you do that is by
mentioning a square bracket you
mentioned hey that's an array which can
hold multiple values now if you want to
imagine this you can imagine a array as
a tray of Cups so let's say from a
kitchen if you want to carry four cups
uh with you to the hall of course you
can carry one cup at a time or maybe two
cups because you have two hands or maybe
you can carry just four cups by dipping
your fingers in the cup but the ideal
way is you can carry a tray now that
tray becomes your array which can hold
multiple cups so that's your array so
why do we need to add it of course if
you want to store multiple values in one
particular variable we can use array
here the beauty is it's not just limited
to three values you can store 100 values
it's just that once you define the size
of an array you have to stick with it
example let's say uh if you want to
define a array let's say num1 and if you
want this to be an array and you don't
have initial values here we at this
point if we talk about these three
values you know what are the values are
but what if you don't know the values in
that case you can say new int array so
you can specify okay so I don't know the
values it's just that I want to create
an array this is how you do it I want to
create a array and you have to also
mention the size here let's say four so
this particular num1 will have four
values not more than that okay it's a
size is fixed you can't increase
dynamically now once we know why do we
need an array let's continue with the
example now once we know why do we need
an array let's start the implementation
so in this video let's try to create an
array now how do we do that in fact in
the last video we have seen our basic
syntax so let's use it so we can simply
create a we can mention the type of the
type of area we are using which is int
and we can give a name to it let's say
nums and then we have to put a round we
have to put a square bracket to Define
that's an array equal to and then if you
already have the values here you can
assign the values itself or you can
specify the values dynamically so here
what I will do is I will put a color
packet here and since I know the values
I can directly put the values here let's
say 3 7 2
four so let's say we have these four
values okay and now I got an array with
four values it's it's that simple the
only problem is how will I use those
values how will I print those values
example let's say I want to print all
the values here or maybe even this first
value let's say I want to print three
because at the start if you remember uh
when we when I mentioned that instead of
using four variables I can use an array
in the four variables it actually makes
sense because every value will have a
different variable name it's easier to
fetch here how will you fetch the first
element from an array now what happens
is if I want to represent that array in
a memory structure what happens is
see if you have one variable you can
create one box right but if you have
multiple variables you have to create
multiple boxes here so one two three
four now this is your array which is
names numbers I've got the same code
which you are doing and then in this
array you'll be having these four values
which is three
seven
2 4. now what it means is if you want to
fetch the value of course in one
variable you have four values now if you
want to differentiate between all these
values you have to use some numbers
right some index numbers uh the way you
do it for the table columns right so we
have numbers in the same way here we
have to give them numbers now if you are
assuming that this will be number one
two three four uh no that's not how your
computer works so add a numbering starts
with zero the point remember it starts
with zero zero one two three now those
are the index values in fact you know
what should I do I should convert that
into different color 0 1 2 3. now this
numbers in yellow color are the index
index numbers for the array okay so
three seven two four there are the
values but 0 1 2 3 is the index that
means if I want to fetch
the values I have to mention nums in
describe but you have to mention the
number which index value you want to
fetch I will say I want to fetch zero
now in this case if we do that let's
compile and run you can see we got three
this is working so whatever value you
have here you're able to print it here
what if I want to change this I want to
print let's say I want to print the
value at number one
so compile run you can see we got seven
so basically you can actually print this
values one by one
okay that sounds good
uh how about updating the value so let's
say I want to change the value 7 here I
want to set 7 to 6. so basically I want
to change the second value and I want
the value to be 6. in that case you can
say index off so when I say second value
it's actually one because the numbering
starts with zero so to say nums of 1 is
equal to 6. now that's how you change
the value and now if you try to fetch
the same value here let's compile and
run you can say we got six
I hope that makes sense uh so basically
you can assign the value you can print
the value as well
what if you want to make it dynamic
okay how do I do that I don't have this
values let's say and then still I want
to create an array in that case instead
of using this syntax here what you can
do is you can say new int and in this
square bracket you can mention the
number the size of the array which is
full now this is another syntax the only
thing is by default all the values of
this array will be zero so of course
you've got four boxes but the values are
zero and if I don't set the value here
let's check what is the current value
for the index number one which is zero
so all the four values are zero uh I
want to change the value so what I can
do is you can specify I want to change
the index value 0 to let's say number
four and the nums of index one so every
every index have to set the value
let's say eight and nums of 2 is let's
say three I'm just giving random values
okay it's not like I have all these
values prepared in my mind but let's say
for three the value is nine okay so we
got these values here now how it looks
like in the memory it's very simple you
got an array with four boxes so the
index value is zero one two three and
the actual value so before assigning the
value of the values was Zero zero zero
zero but now since we have assigned the
value of the number the value has been
changed the values are four eight three
nine okay yeah so for eight three nine
those are the values you have
now this is how you store the value now
if you can also fetch the value let's
see what happens so at number one uh
index number one we have value which is
eight and you can see we got eight so
this is working but what if you want to
print all the values now that will be
tricky uh let's try so what you can do
is if you want to fetch all the values
of course you can just print this
statement multiple times
right the only difference you have to do
is you have to say index of 0 index of
one index of 2 index of three and you
can simply fetch all the values right so
compile
and then you can see we got all the
values this is working yeah but don't
you think we are doing the same thing
multiple times it's just that the
numbers are changing that to in sequence
you know what we can do here that's
right we can use a loop so I can just
remove all the extra statement just by
using one statement I can put that into
a loop now the main question is when I
start a loop here the loop will start of
course you have to say int I but what
should be the initial value for I
it should be zero you know why because
the index value starts with zero and
then less than should I say equal to
we can we just have to say 3 there
because the size of the array support
you have to stop at 3 and I plus plus
that's one way or you can say less than
four whichever format you follow
okay and then just put that into a curly
brackets now we can just shift this
statement in the block so that it will
execute so basically we are using a
forward Loop to to print this now the
only thing is if you can say we are
mentioning 0 which means it will the
loop the loop will run for four times it
will simply fetch the index 0 I mean
zeroth element every time or first
element every time we have to change
this we have to make it I so that the
value of I keep changing here and you
will get new value at a time every time
so compile and run you can see we got
the values so this is how you can use an
array of course there are a lot of
things related to array how can we
create multi-dimensional are they can we
use a different kind of loop so till
this point we were able to understand
what is an array right so basically we
have seen this example where uh you know
we have an array which has four elements
right we have three seven two and four
now if you look at this can you say this
is array of elements of course it makes
sense right so we can say this is array
of elements now can I create something
like this let's say I want two different
arrays so I got this as a first array
let's say four elements and whatever
elements we can have here let's say five
two six one so we got this array and
then I also want one more array here
right let's say we got in fact we need
two molari and of course they will have
some values it doesn't matter I'm not
concerned about the values as of now we
have some values there okay and of
course every array need to have a name
for it so can I say this is uh N1 array
this is N2 array this is N3 array we can
give any name to an array right in this
case I'm just naming them as N1 N2 and
M3
okay so if you're going to have multiple
values as one array can we have multiple
arrays combined to form one big array
what I'm saying is can we just have an
array of array something like this that
looks weird but can I use a different
color just to make you understand this
what if you can just have an array
so this is a big array which has three
elements and this particular array the
bigger element let's say the outer array
we name it as uh
nums so this nums array will be having
three different arrays
that sounds good right now this is
called
multi-dimensional array so ignore my
spelling that but this is called a
multi-dimensional array now how will you
represent this it's very simple
uh if you want to represent this we can
simply say hey I have a nums array which
is multi-dimension which will have array
of array the way you can achieve that is
very simple you just have to put two
square packet because one square packet
represents that's an array now can we
say the nums array is of array of array
yes we can and we have to mention the
type as well so it will be of type
integer let's say and then you have to
say new and you have to mention again 2
square bracket now but what will be the
values here see if you have a single
array it's very simple you can just say
the size is 4 but here if we talk about
the size how will you define it so if
you compare this particular thing can we
say we have one big array which has
three internal arrays to it so can I say
this is three internal analysis and each
array has four elements let me repeat
in this big array nums we have three
small arrays and each array has four
elements okay that's how you define it
now how will you assign a value to
everything so what you can do is if you
want to represent that in a good diagram
here what I can do is I will just draw
that once again
so we have one big box and in this box
we have three sections and each section
has array
and each array has four elements one two
three one two three simple right now how
will you give numbers to it so outer
array will have number as well so it
will be 0 0 1 2 and each array inside
will be having their own indexing uh
let's say 0 1 2 3. now let's say if I
want to represent a particular element
here now what element so let me assume
it what element I'm talking about let's
say I want to Target uh this element in
fact let me just fill some values here
five two six one uh three two one seven
four eight one two random numbers okay
nothing in my mind I'm just giving
random values Here and Now I want to
Target let's say the first value five
how will you target five what will be
the output for how will you find this
value
so 5 here becomes 0 comma 0 simple right
because this is zeroth row zeroth column
uh if I want to represent this six so
this 6 would be 0 comma 2. if you want
to represent this 7 so what do you think
in your mind if you can think about this
this will be 1 comma 3 and if I want to
represent this 4 here this will be 2
comma 0 this 2 would be
2 comma three okay that's how you
represent the values here quite simple
right so let's try to create this in a
code now so what I will do is I will
just remove all the extras things from
here I don't want student anymore and
let me just simplify this stuff all the
code gone
and I'm I'm just assuming that you are
doing The Code by yourself after
watching each video and that's how you
do it right it's not just about watching
videos it's also about implementing it
uh so what I will do now here is I will
just create a array of nums but this
will be a two dimensional array or a
multi-dimensional array and I can say
ain't
here so we want three rows and four
columns now there are different ways of
saying there's three rows four columns
or I can say we have three rows and each
row has one particular array of size
four as simple as that and here I can
just come back and I can by default all
the values are 0 right and in fact let
me just do that let me print all the
values now how do you print it we can
use a loop here now the only thing is we
have to use two loops
or nested Loops we have talked about
nested Loop before as well but let's try
so what I will do is I will say int I is
equal to 0 and I less than equal to okay
I less than now what should be the value
it should be 3 for the Outer Loop and
then I plus plus and then for the inner
loop see the outer loop will hover
towards all the rows now we have to go
inside the row as well so to go to
inside the row we have to say I ain't I
mean J is equal to 0 and J less than 4
and J plus plus
and here let me print the value so I
will simply say nums of
so what is representing the outer loop
it's I which represents the outer box
and J for the inner inner box because
for every row we have to start from 0
again right example if you see here
uh it will start with 0 and then for
every row it will go for 0 1 2 3 right
once you reach 3 here it will jump to
the next row and again it will start
from 0 1 2 3 then it will jump to the
last row and then again it will be 0 1 2
3. right so if you want to represent a
number you have to say nums of I and J
because I represents 0 and J represents
every column here okay let me just run
this code let's see what happens I will
say clear
compile and run you can see we got all
zeros
maybe you wanted to print this in a box
structure what you can do is instead of
printing Ln because Ln will point on a
new line you can say let me print a
value and let me also give a space here
for after every number and then once you
complete the inner loop once you print
one row just come on the new new line so
I will say just print again it will come
on new line
let's see if this works compile
run oh we got it so we got a two
dimensional array right the only thing
is I want different values here so I can
assign but I can assign them manually I
think this is a good time to talk about
how do you fetch the random values so
you know we have this math class in Java
which will give you some random values
right so this is a inbuilt class which
will generate a random value and to
understand that let me just go to the
random function random function returns
a double value so it returns a double
value if I store that value in temp or
maybe random the variable name is also
random the only thing is will not get
integer value and also I guess the
random function gives you a value which
is in points decimal points greater than
or equal to yeah basically it will give
you value less than one so what I can
simply do is I can multiply the number
by 100 let's see what happens so
whatever value I receive I will just
multiply that by 100 again right I'm
just doing some experiment here now once
you multiply that we have to also
uh do a typecasting now we have to
convert that double value into int now
whenever you want to convert something
we can use something called a type
casting so double value will get
converted into int here and I don't want
this to be generated on only once so
let's change the value for I will just
cut this part I will use it later
initial value for random is zero
and I want to find the new value every
time to assign the values here
and I can simply use the same Loop right
let me just print that statement
so that I will have it somewhere
and I will just copy and paste it here
to assign the values this time I will
not print values I will assign the
values
so I can say nums of
I and J is equal to
this value this formula I think this
should work I I just I'm not sure what
will be the value it will assign but no
we don't even need this variable
basically
but how do I know what value it is
printing so let me also print the value
of what it is assigning so that I will
know what is happening so compile
and run oh it's assigning zero values
why I think it should be typecasted
after we do the calculation compile run
oh got it so you can see we got this
random values uh so what was happening
before is we were typecasting the random
values and then we were multiplying by
100. what you have to do is since random
will give you in point values like 0.12
or
0.74 so all these zero point values we
just have to multiply that by 100 so
that you will get a double digit number
at least and you will simply Typecast it
later of course it will have 72 points
on values I'm just typecasting it
and then yeah so let me just remove this
printing so that you will get the exact
box here
compile and run if you want single digit
I think multiplying by 10 should work
I'm just assuming yeah A1 multiplying by
10 works because we only want single
digit
yeah that's how you Generate random
values that's how you print it
the random values are fun yeah so one of
the library which we have used is math
okay we can do one more thing here so
while printing we have used a normal for
Loop right can we use uh enhanced for
Loop can we let's try so in enhanced
model what you do is you use a for Loop
and then from the array it gives you the
first element right now coming back to
our drawing board here if we talk about
this particular array or this array here
it will give you one value at a time
right so we can simply accept that in an
integer variable but what if two
dimensional array here if we talk about
hey nums I want the first element Norms
will throw the entire array to you it
will not throw one element it will throw
the entire array and that's what you
have to handle so here you can say ain't
I will say n
now n here is not a simple array or it's
not a simple variable it's an array
itself it is coming from nums okay so
let me repeat n is not a simple variable
it's an array a single dimensional array
so we have to say with square bracket
now once you get the array from that
array we have to get the first value
so we have to use one more Loop here and
we have to say m colon n now m is taking
the value from the array of N and then
we can simply print the value so I will
just remove this bracket I will say
print M because that's the element and
with that I also want to give a space
and now here I just want to write into
in the second line okay so both are
doing the same thing let me prove I'll
clear this
compile run so this is printed by the
first Loop this is printed by the second
Loop the enhanced for Loop so that's why
we use two dimensional array with
different types of Loops so let's say we
have talked about multi-dimensional
array right now in multi-dimension Array
of course you specify the number of rows
you want so if you look at the code here
we have specified what are the rows we
have and in each big array we have add a
small array which is of size 4 right
and then we were assuming that every row
or every array inside the array will
have the same size example if you look
at this three
areas here they have the same size but
what's the guarantee that they will be
having the same size what if you have an
array here which is of size three uh
here you have a size four here you have
a size two can we do that
can we have the internal arrays or the
columns basically having less values
it is possible so what I'm saying is
this 4 is not fixed we can simply say
hey I don't know the number of columns I
have
yes we can do that so the internal array
or the inside array can have different
size of elements now this type of array
is called a jagged array so before this
we talked about normal or regular arrays
where you have you have to specify the
size at this point we are not doing that
see we have to at least specify how many
areas we have but internally those are
those rows we don't have to specify how
many columns we have
that we can manage but how how we are
going to manage so what we can do is
once you specify that I I'm not sure
about the number of columns here which
is dag data then we have to individually
specify how many columns you have what
I'm saying is you have to say index of 0
is equal to for the first ad you have to
specify how many values you have so you
have to say new and three so that's the
first thing we have and then likewise we
can specify the other values I can say
copy paste and paste for the first index
I have the size let's say four for the
second index I have a lesser size two so
that's why we to manage this one now
this is your Jagged array okay I mean
this one this is your jack Daddy not a
normal array because individually for
every column we are specifying what's
the size of it now if you if you try to
imagine this in a new structure let me
draw it here so you got a box this is
the outer outer thing and in this you
have three rows and each row will have a
box now the first box will be of size
three the second box will be of size 4
and the third box will be half size two
okay so we have different size of array
in different at different location so
for zeroth index we have three for first
index we have two or sorry four for the
second index we have two that's what we
have done here okay now once we specify
that the thing is how will you save the
value inside this now the problem is the
number of rows are fixed but I don't
even want to mention the number here the
way you can solve that problem is by
saying
Norms of or maybe you can say nums dot
length this will this will show you the
number of rows you have but for every
row okay in fact you know what we should
do we should save that value somewhere
um or maybe we can say this nums of I
for every row
I want to know the size
so now basically we have we have
specifically the size of each array so
for the first array I have three values
for the second I have four values so for
every row how many what's the length we
have we have here that's what we are
specifying
and now while printing as well instead
of using normal for Loop let's use
enhance for Loop and the beauty about
now enhance for the paste you don't have
to mention the size anywhere it will
automatically detect where the values
are
okay so if I try to
compile this code and run you can say
this is the values you have the first
row we got three second row we got four
and the third row we got two okay now
this is the jagged arrays so once we
know about Jack Douglas let's go back to
normal array what we can also do is we
can skip this part now can we create
three-dimensional array we can every
time you want to increase the dimension
you just have to specify extra square
bracket and extra Loops for every every
square bracket so now you can imagine if
I want to draw this I don't know how do
we how do we draw this but let's try so
we have the outer box in which you
specify how many rows you have we have
three rows zero one two in this you have
an array of size 4
so one two three four and in each box
you have one more array here which is of
size five okay let me just do that in a
small let me expand this
and in this we have one more array of
size five okay uh this is index number
zero one two three four and then this is
zero one two three so if I want to fetch
this value here which has value X is six
if you want to fetch this six you have
to say zero comma zero comma two right
and of course in every box here we'll be
having the same thing we have the box
here which has four elements and each
box will be having multiple arrays yeah
so we have added here as well and if I
want to fetch let's say the third
element here we have to say one comma
one comma three okay that's how you
fetch it so the more array you create it
will create a box internally to it so
that's how the array Works uh now this
is not jacked anymore this is
three-dimensional array so I hope this
makes sense uh we have talked about Jack
that is and three-dimensional in one
video in this video let's talk about the
drawbacks of array of course we have
seen a lot of good things about array we
can store multiple values and then we
had some fun with the multi-dimensional
array and the 3D array Jack that is but
let's talk about some drawbacks what I
will do for that is let me remove the
entire stuff and let's create a single
array here so let's say when you create
an array of norms and let's say this is
of int type so of course you have to say
new int and you have to give a bracket
under this was for the size four now
first of all we
all beeping Java is an object okay the
moment you're saying new keyword that
means it's an object right it will be
created inside the Heap memory but what
it does is the moment you say this line
inside the Heap memory it will occupy a
space and the memory location it will
take is Conti it's continuous okay which
means it will simply occupy the space
continuously and the problem with this
is once you specify the size here you
cannot go back so once you say four now
you cannot expand the size it's fixed so
in future if you want to create or if
you want to expand the array you can't
see one of the solution what you can do
is you can at that point if you want to
say hey I want to increase the size of
the array just create a new array of
that size and copy all the elements
that's a solution but it will also
consume some time and there will be some
computation will be happening so if you
know the size is fixed you can go with
add a the second problem is every time
you want to search something it will
Traverse between the elements so for
searching for inserting value it does
consume a lot of time the last problem
which is we we mentioned about Interior
right but what if you want to have an
array of different types let's say if
you want to have integer string double
in the same average unfortunately you
can't do that I mean there's a solution
uh if you want to have object of student
integer string there is a solution of
object but that's not that's not an
optimal solution so again they are not
really a drawback what I've talked about
they that's how the array works but then
you know when you say something is
drawback you say that's a drawback
because there is something new which
came up which has all these features now
the concept which I'm talking about is
collections now this is not a good time
to start with collection it will come in
later but uh just because of collections
we are talking about some drawbacks of
adding but other Addies are great they
are fast you can store multiple values
but yeah there are some things which
might have been done to improve it but
that's where we have collections right
we'll talk about collection later and
it's not like just because of collection
will not be using ad anymore they have
different use cases every time you know
you have a fixed size and if you want to
store multiple values as they will be
the first preference so once we have
talked about array I mean basically
which we have talked about why do we
need array and how to create an array
let's do something more with that in now
in fact in the previous video we have
seen how to create the array and then
how to print the values now in this
video let's try to see if we can find a
better way of printing this value see
what is happening now is let's say I
mean of course we know the length of
this array here right which is four ah
it can also be five or any numbers I
mentioned before right it can be 100 200
or whatever size you want to mention and
you can insert the value now before I do
anything else I just want to show you
one more thing what if the value of the
size of array is 6 and you are assigning
only four values here now in that case
the other indexes will also have some
values right let's see I just want to
see what are those values before we
continue
so compile and run you can see we got
the values but then the last two values
are zero remember we have talked about
this by default the values for the array
or integer array will be zero
and that's what is happening Here and
Now what I'm going to do is I want to uh
see if I can get this value see the
thing is why I should know the length of
the array it might also lead to errors
example if I say 7 here by mistake and
if I try to fetch the value see this is
where it will give you
an exception now till this point we have
not talked about exception of we have a
separate topic what are exceptions at
this point just remember exceptions are
runtime errors okay so the address which
comes in runtime at compile time there
is no problem when you compile this code
it will not uh blame you it will not
shout but the moment you run this code
it will say hey something is wrong here
so that's exception now what is the
problem the problem is we have six
values index number star starts with
zero it ends at five not at six and here
it says index 6 is out of bounds so
basically we are trying to go beyond the
limit okay so how do we solve this
problem so instead of specifying the
number hardware values we can do one
thing you know this arrays they have a
property called length so we can simply
use this length as a variable or a
property which will show which will tell
us what's the actual length of the so
that you will not make any mistake the
only thing you have to remember is you
have to put that you have to make sure
that it's less than not greater than
okay and I will I will clear this I will
say compile and run you can see we got
the values and there's no problem the
only thing is the size is 6 and then we
are printing only we are assigning only
four values let me go back to four
values and you can see we got four
values here
now this is one of the good addition in
terms of the property which you can use
so that's about length here now what we
can do is uh let's say if I want to have
a string array or maybe I let me create
a array of student can we do that uh so
remember one thing so if I create a
student here and of course I can create
one object I can get multiple objects
here and let's say I have a integer I
have a student which has some values so
let's say integer roll number
okay and the string name and int marks
of course not a good way to uh maintain
the records we don't want to maintain
marks but just for the example okay so
we have student and then we have these
three variables okay now mind you these
are the instance variable because they
belong to a class not to a method I just
want to comment the entire section here
and what I will do is I will create
student object so let me create the
first object I will say student S1 is
equal to new student and I want to
assign all the values to the student so
I will say S1 dot roll number which is 1
and S1 dot name which is let's say
Naveen and S1 dot marks which is let's
say 88 okay so we got the first object
now maybe I want to create more objects
what I can do is I can just copy this
code and paste and let's say three
objects so we want three objects here
and I will say this is two this is three
and let's say well number two let's say
this is hush and marks let's say 67 and
if I say this is 3 let's say this is
kitten and let's say the marks is
97. okay so we got these Marks here
right and then basically they have your
objects now I I made one mistake here if
you can I don't know if you have
observed but if you can see I'm still
assigning the values to S1 don't you
think it should be S2 S3 uh so it should
be S2 S2 and S2 and there here we have
to say S3 S3 and S3 so basically we got
three objects here now what I will do is
I want to create an array of students
right we have created the array of
integers but then how do we do that
array of students it's very simple you
say student and then you have to say
students because we are creating
multiple students here that's a variable
name equal to now this students here is
not one variable it's an array so I have
to say array and then we have to say new
now in this case when you say we have
INT in the same way here it should be
student
right student array of let's say three
students will be having so all these
objects you know we got three objects
here S1 S2 and S3 they will become part
of this array example I can say student
students of 0 is equal to S1 so the
first object the first reference is
getting stored here in the first index
and likewise we have this is S1 S2 and
this is S2 S3 so you can see we got
three objects in the array so of course
you need these objects otherwise this
will not work now if you are thinking at
this point we are creating present
object no we are not getting three
student object most of the people have
this confusion that on this line we are
creating three student object now we are
creating an array which can hold student
references it will not create those
object by itself
you have to manually create the objects
and assign to an array now this thing
will make much more sense when we start
working with databases when you fetch
data about a student it will give you a
lot of data you can basically fetch
those data in a student array now what's
the advantage the advantages let's say
if you want to print all the details of
a student so what you can simply do is
you can use an array which will start
with 0 and I is less than equal to okay
I is less than students dot length which
we have seen and then I plus plus and
then here we can simply print but how do
you print the values so what we'll do is
you have to print one value at a time
you have to say S1 because if you try to
fetch the value of a student it will
give you a address format okay example
let me show you something at this point
uh let me just comment this section and
let me print the student object itself
and let's see what happens so if I try
to print the S1 value
you tell me what will happen what the
what will be the output
I mean think about that I will just
compile this and run you can see it is
not printing the value of a student it
is printing something else see in the
upcoming videos will solve this problem
at this point it's printing the address
and we don't know what this is so what
we can do is explicitly you have to
mention S1 dot name and you have to
maybe you can do a concatenation here
and you can say S1 dot marks I just I
don't want to print the roll number at
this point so I'm printing on you this
too and now if you compile and run you
can see we got the student details okay
so can we do it here so let me just
uncomment this section the only thing is
you have to print this particular
statement cut
and paste now the only problem is it
will always refer to S1 we don't want to
refer to S1 right the student value will
keep changing so I can say students
square bracket I right so this value
will keep changing right this will be S1
S2 S3 in every iteration the same can be
done here
so I can say students of I that should
make sense and let's see if this works
let me go back here compile
and run you can see we got the values
right so basically we can work with
normal objects as well uh before this we
have worked with integer of course you
can work with string as well but we just
went uh one step ahead by creating an
array of students okay so I hope you got
some idea regarding how do we get an
array of students in this video we'll
talk about for each Loop now why do we
need another loop when we already have
this particular Loop here
okay for that let's understand let's
comment the entire section from here
because I want to use uh the simple
example which we already have here right
so if you remember we have worked with
this array which has four numbers so
let's work with normal integers now if
you want to print all the values this is
what we did right we used a normal
variable normal for Loop in which you
have a counter I which starts from 0 to
the last value of the length of the
array less than that which is three and
we were able to print all the values the
only thing is why you need to do the
counter and then you have you should
also know the length of the array and
then you have to specify the index value
here to fetch the value I mean this
works but then can we have a better
solution for this and that's where we
got an amazing Loop which only works
with array and array type of data so in
future we're going to talk about
collection as well and that also it is
used but since we only know addeds at
this point let's try to use another type
of loop now think about this can we just
say hey for Loop you know what I want
you to do
iterate between all the values and give
me one value at a time and of course I
will decide what to do with that value
example here as well we are able to
fetch a particular value of uh array and
then we can do whatever we want to do
with that of course at this point we're
just printing it but we have an option
of doing multiple things here as well I
would say hey for Loop you gave me a
value not the index number
give me the value
so what Loop says okay okay let me try
so whatever value of order will give you
you can store that in n a variable but
then from where you will get the value
you will get the value from the nums
with which is the array so I can give a
colon and we can say nums this is the
Syntax for for each loop I know this
will be confusing at the start but once
you get used to it you will love it what
is happening here is if you compare with
the upper Loop in the upper Loop we are
using a counter here we are not using a
counter we are simply saying from these
nums I it doesn't matter how many values
you have four values 10 values 50 values
I don't care you just give me one value
at a time and that one value will go
into n now you can decide what to do
with that at this point just to keep it
simple we are printing it okay so you
can see I just got the value n and I'm
printing it no I no counter no increment
no need to check for the length no
exception right and uh this is a beauty
about it it will just iterate between
the nums and iterate till the last
element so if you had five elements it
will iterate five times if you have four
elements it will iterate four times and
every time it will give the value to n
and that's what you are printing it here
let me prove that let me just compile
this code and run you can see we've got
the values
this is better right you can also use
this with the thing here which we have
done for student I will just comment
this part
and uncomment the entire section from
here
everything is uncommented the only thing
is I don't want to use the novel for
loop I want to use the enhance for them
so normally instead of saying that this
is a for each Loop we say enhanced for
Loop okay so what we can do is we can
say for and here okay the only thing is
when normal photo we use ain't because
we want to maintain the counter if we
talk about the example which we have
done for normal integers here also we
use we are using int because the type of
values in nums is int but now we are
working with students right so here when
you say student let's say stud colon so
we have to mention the student type not
int because from the students array you
are getting a student reference and you
will get the values from students so it
doesn't matter how many students you
have it will fetch one student at a time
and then with that student you can print
the same thing
so whatever you're printing here you can
print that here the only thing is this
two represent one particular student at
the time so you can simply say student
dot num and you can just concatenate so
what we are doing here is we are doing
concatenation the student name and then
we are giving a colon so to do that we
have to use a plus operator in between
to concatenate and I can also say stood
dot let's say marks let's see if this
works now we are working with student
not with normal variables compile and
run that's it you got the output so you
got Naveen and you've got number so this
is your enhanced for Loop yeah some
people do say it's a forage Loop but
let's call it as enhanced for Loop
because in the upcoming in the latest
version of java not the latest one I'm
talking about Java 8 which came way back
it has a forage method so just to not
get confused let's call this as a
enhanced for Loop now one of the reasons
why people say it's a foraged loop is
because in other languages this type of
Loops are called for it that's why in
Java also people have a tendency to call
it forage but let's call it enhance for
Loop so I hope you got the idea and I
would like you to work on this practice
this otherwise it will be confusing so
practice this multiple times and you
will get used to it it's time to talk
about a very simple concept and complex
at the same time because to use it's
very simple but when you try to
understand what is happening behind the
scene that's where it gets complicated
so let's try to understand that in this
topic of string so in this we'll just
talk about what is string now basically
we have worked with string before
example whenever you try to create a
variable we can have we have to specify
the type of it right example we have
worked with integer float double Boolean
in the same way if you want to store
a character stream let's say if you have
multiple characters something like this
let's say uh you want to store a name
like Naveen now this Naveen is not a
single character right it's a bunch of
characters and when you want to store
this together of course you can use a
character array we will talk about
either later but then we can create a
character array here which is a array of
different uh different characters or we
can create a string here now how do we
represent that in a string now one thing
to remember whenever you talk about
string in Java you have to put that in
double quotes the way you work with
characters in characters you use single
quote here we'll be using double quotes
So if you want to store Naveen so you
have to first put that into double
quotes and then where you will store
this of course you have to you you need
a variable here right so what I will do
is I will create a variable called name
now this variable name needs a type now
what type of this this is of type string
now one thing to observe when you talk
about primitive data types we have end
float double character uh Boolean and
many more right now all those actually
starts with small letter right uh this
string s starts with capital which means
that string in Java is not a primitive
type it's a class basically if you go to
string class you will find string is
actually a class
okay that actually makes some sense but
then when you say class we have seen
this right whenever you work with
classes and if you want to create object
of it we use a new keyword right we are
not doing it here so this does not look
like a correct syntax it works but it's
not something we are used to right
whenever you work with class we normally
create a new object
okay this works but then why this will
work that we'll discuss later at this
point if you want to go in a general
sense if you want if you have a class
the way you can create a string is by
the way you can get object of string is
by saying new string and you can give
the round packet now this is how you
create a string variable a string object
now basically this is a variable right
reference variable which is referring to
a string object now what might be
happening behind the scene so it's very
it's not that difficult uh if you
imagine this as your jvm The Big Box
inside this of course you will be having
your stack memory right now this is your
stack and then of course in this uh you
will be creating a reference variable
which is name and then it will have some
address but this address or the object
will be created inside Heap memory
imagine this is your HEAP memory you
know we should make this a big one this
time let's say a bigger Heap memory so
that I can write some multiple things
there now the reason we are creating a
heap memory in another structural format
is because there is no fixed size to it
it may expand depend upon your
requirement so we got a heap here now
when you talk about this line line
number eight when you say new string of
course it will create a new object for
you you got object here right and it
will have let's say some address I will
say the address here is one zero five so
of course you will create a variable
which is name here and then the address
is one zero five so there's a link here
and of course in this particular box
there is no data it's it's empty right
okay uh this empty makes sense actually
but then if you try to print this let's
try let's see what it prints if you try
to print this data here I will compile
this code and run you can see it spin it
prints nothing basically it prints blank
thing
okay it's because it's blank now how
will you provide data now in this case
what you can do is in this new string in
the Constructor you can pass this string
whichever you want to example if I want
to store Naveen that's the D time
storing ignore this original this is
given by the IDE but this is our value
which is Naveen so inside this string
Constructor you are passing the data
which is Naveen right now if you try to
print this you can say we got Naveen
here okay so that means in this thing uh
we are creating the data which is Naveen
that's what we are expecting as of now
let's see if that works okay now there's
also a concept of hash and equals right
so what I will do here is I will try to
print the hash code for this one so if
you try to print the hash code and if
you run this code you can say this is
the hash code for this depend upon data
depending up on some calculation now
what else we can do here so example
let's say if I want to concatenate this
Naveen with hello so let's say I want to
print hello Naveen what you can do is uh
of course you can write a different
statement to print hello and then you
can print the name but then string by
default does not work with any other
operators like subtraction division but
only there's one exception which is plus
orbital so you can use string with plus
operator
okay so let's say I want to print hello
and Naveen both so in this case you can
print hello and then to concatenate to
mix this two you will use a plus
operator here so you can simply say plus
and now with this compile and run you
can see we got hello nabin I hope that
makes sense
so you can use plus to do to print this
what else we can do uh we have certain
methods here which we can use now since
it's a class of course it will have some
methods right so there are some handy
methods here example you can check uh
what is a character of a particular
location so let's say I want to know
what is a character at location two I
mean index number one
so if I pass index 1 here
it will give me a character at index 1.
so if you look at this Naveen it is n is
index 0 a in is index one then two then
three then four and if you try to
compile and run this you can see we got
a so yeah this is how you can basically
use certain methods there which is
character add or you can also
concatenate two strings okay so let's
say if you concatenate my name with I
will give a space and ready so basically
what I'm doing is I'm concatening Naveen
with ready here let's see if that works
okay so that we got Naveen ready so
that's how we can basically use this now
since strings are so important for the
programmers what we got here is uh
let me just remove let me just remove
this line yeah so string is so important
for programmers what we got in Java is
instead of writing this new string you
can actually you know directly write
Naveen here even that works so behind
this it will create an object you don't
have to worry about it so when you say
string name equal to Naveen it will
create the object for you you don't have
to worry about object creation of those
stuff so most of the time you will see
this syntax hardly you will say uh
string name new string and then Naveen
that's hardly anyone do that so this is
famous and it even this works you can
still try this out and that's why before
when we were using string we directly
assign the value it was working so in
the previous video we have talked about
string right now we talk about this
string
uh what might be happening behind the
scene example let's say if you store
this Naveen of course it will be getting
stored in the in the hip memory but now
what I want to do is before printing
Naveen here let's say I want to append
something so let's I will say name is
equal to I want to add my name with
let's say ready here I'm giving a space
so that we can differentiate these two
words so of course now when I say name
it is will it will be Naveen ready right
so basically we are trying to change the
value now if we talk about integer float
double basically you can change values
of it right and it actually makes sense
that's why we call them as variables
and here also we are trying to do that
but first of all let's check if this
works
so if I go back and compile and run it
works you can see that the new data for
the Naveen is Naveen ready right and
that works but what if I say that's not
the case you're not changing the
existing string let me repeat
you're not changing from Naveen to
Naveen Reddy so if you're thinking there
will be a variable here where you have
Naveen you're making it Naveen ready uh
no that's not the case that's not how
string works okay so what happens so
what I would what I will do is I'll just
remove this part now so what is
happening basically
you know since strings are used heavily
in Java now most of the time you try to
reuse the strings the same string you'll
be using multiple times example let's
say uh if if before I show you something
let's say I create a string here which
is S1 is equal to Naveen
and you can see we have a capital M this
time so this two data are actually
different
okay so I will say string S2 is equal to
and I will say Naveen again now what do
you think how many objects we are
creating behind the scene think about
this okay so if you're thinking we got
two objects actually not
we got two references we got S1 S2 of
course in your stack you'll be having S1
S2 here
but
in total you got only one object
I know that sounds tricky here right and
let me prove that point to you uh see
what I want to prove is the value for
this field and this field will be equal
the way the way I can do that is by
saying s out S1
is equal to equal to S2
if this is true then they are same so if
I run you can say it got true that means
the value for the addresses are same in
total we got only one object so here
what happens is we have a special area
inside your hip memory so this is your
HEAP that's your jvm and that's your
stack so inside your hip you will be
having a special area called string
constant
pool and by the name itself you can see
it says constant that's right every
string which you create which you use in
Java which is a string literal is
actually a constant you can't change it
example if I if I write something like
Naveen here I cannot change it it's done
it's Naveen everywhere okay so you can't
change the data so example what happens
is every time you try to use a variable
example if you execute the line number
eight it checks okay we need Naveen
variable do we already have Naveen in
the string constant pool no we don't
have it so let's create Naveen here so
it will create a string variable Naveen
it will have some address let's say one
zero one and then the name variable here
will get this address so this name
variable is actually referring to this
particular address
okay then it goes for the next statement
let's execute this part Let's ignore
this line as of now let's focus on line
number 12 and 13. so line number 12 says
S1 is equal to Naveen okay so it checks
do we have Naveen with capital N in the
string pull no we don't have it so it
will create Naveen here and let's say
the address is 1 0 3 so it will store
103 here okay now that makes sense right
and that's why you're referring to that
particular location
now what happens on line number 13 line
number 13 says string S2 is equal to
Naveen it will go to string constant
pool again and check hey do we have
Naveen with capital n yes we do have now
it will not create a new object for you
it will simply use this address one zero
three okay and that's the beauty yeah
that's how you're trying to save the
memory otherwise you have you could have
created multiple variables with the same
data so it doesn't make sense right and
that's why it uses a string constant
pool now my question to you is what is
happening here now when I say you can't
change the data that means you cannot
simply update this particular Naveen by
Naveen ready no that's not happening the
wind is still there it will be it's a
constant you can't change this now on
line number nine what is happening is it
is creating a new object which will have
a data which is Naveen ready it let's
say it has the address which is 105. so
on line number nine basically what you
are doing is you are changing this
address from one zero one to one zero
five you're just changing the address
you're not changing the actual data you
are basically creating a new object okay
now you might be thinking what will
happen to Naveen here the thing is now
this particular object is eligible for
garbage collection it will be removed
after some time just to get some memory
back okay so Point remember is once you
create this object you can't change it
and that's why we have some terms to
remember and the terms are so there's a
concept of mutable strings and immutable
string now what is mutable means mutable
means change something which can be
changed and immutable means unchanged or
you cannot change it
so basically by default strings are
immutable once you create the object you
can't change it and that's very
important remember it's immutable string
okay so whatever data you're creating
here is immutable but what if you want
mutable string and that's why we have
two different classes in Java to use
instead of using string you can use
something called a string buffer or a
string Builder now both are very similar
with one difference that difference will
discuss later but they both are similar
and they both provide you a way to
implement a immutable string okay in
this video we'll work with string buffer
so what we have is we have a string and
where we have worked with it right so
what I will do is remove everything and
let's work with string buffer so I will
say string buffer and let's create a
reference for it equal to new string
buffer now when we talk about string
buffer of course in this string buffer
you will have a string and which is
actually mutable you can change it now
to make it more efficient you know what
string buffer does string buffer will
give you a buffer size okay which is of
16 bytes so I can just try to print that
first I will say SB Dot ah so we can
know the capacity of this string buffer
even if it is empty it will give a
capacity of 16 characters and you you
got it there in fact you can also
provide some initial string here so
let's say uh if I say Naveen here now
Naveen is of five characters right this
is how you basically create a string
buffer in bracket you mentioned this
string so it will create a string of the
object and the beauty is you can change
this data okay now the thing is uh if we
talk about capacity what it will be so
capacity is should be still 16 right no
it actually changes if you can see the
capacity will become 21 it's because it
will store my name and it will also give
me a 16 space extra
now why it gives me that space is
because every time you change data and
if it consumes a continuous memory
location inside your hip memory and what
if there's no continuous location next I
mean what if there is no location
available there is no space available in
that case it has to relocate so to
reduce the relocation of the string it
gives you a buffer
okay so that's the capacity and now we
know how it works we can also print the
length of the string we can say SB dot
length and length is available in normal
string as well so if I compile and run
you can say the length is five so length
n capacities are two different things
okay now can I append data see the
ultimate thing was can I change my data
which is Naveen in this case the beauty
is string buffer will give you a lot of
different methods to do that you can see
we have a method called append so you
can use append and you can append any
data which you want to so let's say I
want to append ready here and of course
I want to give a space between Naveen
Naveen and ready so you can append and
you can print the data so you can print
SB as it is let's first we have to
compile the code run and you can see we
got nothing ready that works next what
if you want to assign string buffer data
to string is example if I do that you
can see it will
give you error it says type mismatch
cannot convert from string buffer to
string of course right STIs of type
string so in that case you can get this
string back uh do we have a method for
it let's see yes we do have two string
we can use that I think that's the only
method we can use
yeah so let's use two string so
basically you can use two string to
convert the string buffer data I mean it
will get the string format it was stored
in Str and you can print it
okay we can use that what else we can do
with string buffer if I come back here
if I say SB dot you can see we have so
many methods here okay so we have append
we have gas it will give you a character
we have done that okay so we can also
delete something we can delete a
character at an index so let's say I'm
going to delete a character at location
two if you try to delete that data
compile and run you can see we got oh
something is missing the V is missing
there because that is at index number
two
okay so the idea is we basically we can
change it and you can experiment it a
lot you can try to use different methods
we can delete
we can insert also in between let's say
I want to insert a Java at the start you
can do that so you can say insert you
can mention the index value where you
want to insert a desert location and the
data we want to which you want to insert
so I will say Java space now what it
will do is it will add Java at index 0.
I mean that is start itself so if I run
you can say it says Java of course you
can add Java in between as well let's
say I want to add after fifth location I
think that should work after the space
is six so let's try that compiled one
you can see Naveen Java ready so it
works okay so yeah that's how we can
basically use insert we have more
methods to explore and I would recommend
you to do that can we see one more we
can also get this substring let's say if
you have a very big string you can
specify the starting point ending point
using substring you can set the length
as well so if you set the length of the
stream let's say I want to set the
length of 30. so if you want to add your
data and if you want to have a specific
length which is study here it will save
the data which is whatever you have now
been ready will be stored and all the
other values will be null let's see so
after Naveen ready it will add some
extra data here okay so that you can
replace that later cool or we can do
that we can also set a minimum or
maximum data I think minimum capacity
method which we can use I think the
method name is ensure capacity yeah okay
so we can say we can we can set the
initial capacity to 100 so it by minimum
capacity will be 100
okay that's how you have different
methods now what's the difference
between string buffer and string Builder
so as I mentioned we also have string
Builder right there's only one
difference string buffer is thread safe
and string Builder is not now what is
thread safe means that will understand
once you talk about thread concept so at
that point also uh we'll talk about
difference between string buffer and
string Builder but whatever methods you
have in string buffer it's almost same
as a string Builder so if you know one
you know the other one as well okay so
that's about string buffer and some of
the methods of string in this video
we'll talk about static keyword from the
start itself when we have written the
first code we are looking at the static
keyword and the question Still Remains
right what is the static so we know what
is method is we know what is written
type we know it is class but again
problem gets stuck here in static itself
now to make you understand this let's
take an example here so let's say we
have a example of mobile phone and every
mobile phone has a brand so brand will
be spraying Services string brand and
and we can have a default value for it
we can have int which is price
and then
string Network
okay and we can also make it for a
specific brand as well but let's keep it
simple let's have a mobile phone
different brands different price
different network and we'll say name
okay now see name itself of a mobile
phone changes right so we used to say
normal phones then we got smartphones
and now we have foldable phones right so
we can have a different name to phones
nowadays every phone is called a
smartphone now because that's how that's
what we call initially it used to call
mobile then we used to call that phone
right so we have a name here as well
what do you call a mobile phone so now
it's a SmartPhone okay so if you want to
work with this mobile phone of course
you have to create an object right so if
I say mobile obj if I will say mobile
obj1 and equal to new mobile and of
course every mobile will have a
different parameter here what I will do
is I will just remove this network just
to keep it simple we just want three
variables here obj one dot brand I want
to set the brand here let's say the
brand is Apple uh since I'm using an
Apple phone here and then the price
let's say 1500 dollars
and what else we have we have a name so
what do you call a mobile phone so um
currently if you talk about Apple phones
or any phones nowadays we call them as a
smartphone okay I know this variable
doesn't make sense but just for the
example I'm saying a name is equal to
smartphone right now if you talk about
this phone here we have all these values
right now of course if I create multiple
objects
it should have a different value of
course every object is different so we
can have a different value to it if I
come back to Apple let's say the next
phone is of Samsung and the price is
let's say 1700 and then we got we also
call them as smartphone okay the only
thing is you have to change it here as
well object 2 obser 2 and then I can
print the values as well
um you know what I will do I will just
create a method which will print
everything I will say public wide so it
should print all the details here so it
should print brand so that I don't have
to print that every time and I will say
price
and I will print name as well now by
doing this what I'm doing is instead of
printing it here every value I can
simply call obj1 Dot show and obj2 Dot
show so it will print its own value not
other values and if I come back here
compile and run you can see we got the
values right nothing complex here the
thing is if we talk about these
variables here they are called instance
variable right now if you create a
variable inside a method that's a local
variable but this are your instance
variable and every variable for a
particular object is different right the
value will be different now what I want
is I want to have the name to be same
for all the objects see because what is
happening is in in your memory so let's
say we have a jvm a big jvm and inside
this you have a stack where you have all
the reference and locations and address
and then you have a heap memory so in
total you can see we got two objects
right one with mobile obj one and one is
object 2 and then of course they have
the address as well so this is one zero
one one zero three and of course this
will be one zero one one zero three and
you will be referring that right so this
is referred here this is referred here
now that's how we can basically use it
and every object will have a different
value but what if I want to have a
common value for all the objects the
problem with this is if I want to make
sure that the name variable should not
be a part of the object because that's
an instance variable now it will be a
part of the object and every object will
have a different value I want this name
to be common for all how do I do that
now if you make this variable as static
Now by doing that what we are doing is
we are making this name variable common
to all the object what I mean by that is
let's say after some time if I say obj1
dot name if I change the name to let's
say a phone here just a phone not a
smartphone anymore if you make this as a
phone and if you see the values it will
affect all the objects you can see we
have we are trying to change the name of
obj1 but we are actually changing the
name of obj2 as well you can say this is
also phone now the reason is the static
variable is actually shared by all the
objects so basically will not be having
individual static variable for every
object we have a common variable which
will be used by all the objects imagine
there is a common variable here name and
all the objects will be referring to the
same variable so if you change the value
for this it will affect all the variable
all the objects okay now this is why we
use static now the beauty is
see why we have to refer brand with obj1
price with obj1 is because every object
will have a different value for it now
don't you think name is a static
variable and it will be common for all
the objects and that's why you can
actually call name with the help of a
class name itself you can simply say
mobile dot name so static variables
should be called with their class name
not with objects you can call with
objects but avoid it and that's why you
can see it gives you warning as well it
says the static field mobile.name should
be accessed in a static way which is
using a mobile uh the class name which
is mobile okay so the point remember
here is static variables are actually
shared by different objects and if you
want to refer to a static variable you
can use a class name so there's a
different area in your jvm where you
have all the static variables and here
as well I should say mobile now the
thing is in non-static methods you can
use static variables there is no harm
okay and that's the point to remember in
the next video we'll talk about what if
you create a static method yes we can do
that you can create static method and
the question is can I use instance
variables there okay we'll see that in
the next video but here we talked about
what is a static keyword so static
keyword means you are making something
as a class member not an object member
so static this name here belongs to a
class not to the object and that's why
you are able to use this with the help
of a class name okay and then yours
you're saving memory as well because not
every object will have their own value
for it or their own copy for it so
that's about static variable now we know
what is static variable static methods
right now let's try to expand this more
to simplify this what I will do is I
will remove the static method for some
time and I will also decrease this code
let's only work with one object now
and here see normally when you work with
variables so we you now we know that
this is an instance variable and this is
a static variable right the name
now to instantiate the instance variable
what we do of course we can instantiate
the variables from here but then what if
you want to instantiate the variable on
this line if you want to give some value
not instantiate if you want to
initialize the variable what you will do
so basically we have seen one concept
right which is Constructor so using
Constructor we can say Okay public
mobile
and we can give some default values to
it right so by default the brand will be
empty string and by default the price
will be let's say 200 right so this is
the default brand default uh text and
default number right which we want to
give what about name I can also give a
default name to a name which is phone in
this case let's say we can do that we
can initialize this static variable
inside a Constructor and there's no harm
in that but the problem is every time
you create an object every time you
create one more object it will call the
Constructor right and don't you think it
makes sense for this two to initialize
every time but why name has to
initialize every time
I feel that the name variable which is
static should be initialized only once
what do you feel of course the same
thing right how will you do that so if
you mention that here of course every
time you call the Constructor it will
install we don't want to do that not to
achieve that we have a special block
called a static block now in the static
block we can basically initialize the
variable the static variable now the
good thing about this is this static
block will be called only once
irrespective how many objects you create
it will call the static block only once
so what I will do is just to demonstrate
that I will create one more object here
let's say
and I will not assign any value to it
just to default values so object to
Second object so it will call the
Constructor two times it will call the
static block only once to prove that
what I will do is I will just print
something I will say in
static block now the Syntax for static
block is very simple it's
static keyword and then you just open
and close there is no bracket or
something it's just a simple block okay
and in the Constructor as well I will
say in Constructor okay and now with
this let me just compile this code okay
there is an issue I have written one
extra okay I have removed the
country package from here so compile and
run so you can see it is calling the
static block only once and just calling
Constructor two times
there's one more issue why static block
is called first
even before the Constructor it is
calling setting block and that's weird
is it the sequence let's try let me just
put this after the Constructor let's see
if there's any make doesn't make any
sense anyway Java does not follow the
sequence but just to
confirm you can see the static block is
still getting called first now to
understand that let's go to the diagram
here see what happens you know with
there are two words we and we only focus
on one word every time you get the
object that two steps one your class
loads
and then your objects are okay so first
your class loads and then your object
gets instantiated so there are two steps
every time you create the object there
are two steps class loads and object
will then will get initialized the thing
is the class will load only once
so basically in your jvm you have a
special area here which is called a
class loader okay and this will have all
the class which are loaded and by
default of course you don't have any
class loaded right so the class will get
loaded from from your library to the
class loader and it will happen only
once so for the first object when it
sees hey there's object creation it will
load the class first and then it will
create the object now every time you
load a class it will call the static
block
now since glass loading happens first
and that's what you will call this edit
block first and then it will create the
object and that's why it will call the
Constructor after select block now
irrespective of how many objects you
create the class is already loaded right
so you can simply create a next object
without loading because it's already
loaded now my question is if that is how
it is working what if I don't create any
object I'm not creating an object now so
if I don't create the object of course
it will not call the Constructor but
what about static block it will not even
call the static block if you can see we
don't have any output oh okay so that
means if you if you don't create the
object it will not load the class as
well but what if you want to do that
what if you want to load the class how
would you do that now for that we have a
special class inside Java which is
called a class class yeah that's a class
okay I know Java has been weird we have
object class we have class class but
that's how it is designed so Java class
if you go there you can you can see it's
a class and it has a lot of methods to
it one of the method which we want to
use here is for name now fourth name is
a method which does one thing which
loads your class and you just have to
mention your class name what's your
class name or the class name is mobile
so in this you can mention the class
name that's it okay the only problem is
it throws an exception okay at this
point we have not talked about exception
but just ignore this line
uh we'll talk about this in detail later
ones which start with the exception
concept but as of now just to make it
work I'm just writing this line ignore
it
what's important is the class dot for
name will load your class if I go to
font name you can see for them is a
method and it's a type method so you can
directly class you can call this with a
class name
and this particular method
do they have any definition mentioned
okay so it says the system class loader
is used so basically it will load the
system class loader to load this class
okay so which class mobile class okay so
now if I just write this line it will
not create the object it will just
instantiate it compile run you can say
it says in New
static block okay that means you're just
loading the class so basically that's
how you load your class you can simply
use the this line to load your class
normally when you build a project you
don't actually use this feature yes
there are some situation where you use
it example when you start a jdbc we'll
talk about this one but we normally
don't use it I'm just using this just to
show you how to call a static block how
to load a class okay I hope this video
makes sense where we talked about static
block to so static block is used to
initialize the static variables
so that's it from this video in which we
talked about static Block in the earlier
videos we have talked about static
keyword static variable static methods
and yeah that's super static now once we
talked about static variable it's time
to talk about static methods now what I
will do is I will just try to remove all
this content from here just to keep it
simple and let's make a static static
method now the method which we have here
show is not a static method right it's a
instance method it's because we have not
mentioned a static keyword now whenever
you want to work with a non-static
method you need to create an object of
it of course if you want to call you
have to create object of Mobile in fact
you know actually we need those objects
here
and yeah let's keep it here just to use
it
now let me create a simple static method
so I will say public
uh static void show one again if you can
see I'm using a different method name
just to differentiate it and here if I
try to first of all I will just print in
static method
now how do we call the static method
to call show we have to get object right
you can't simply come back here and say
mobile dot so this will not work if you
try to call mobile.show it will give you
an error it says let's see the error it
says cannot make a static reference to a
non-static method that means you cannot
call a non-stick method with the help of
a class name and that's why you need
object here which we can see we're using
obj1 object two
but can I call show one from mobile
let's try and we can you can see that
there's no problem
so you can call a static method directly
with the help of a class name
okay that's what we are doing here we're
actually calling it with a class name
now the question is this looks cool
right starting method can be used
directly with a class name but can I
call can I use us variables here let's
try to do the same thing I will just
copy this line and paste it here let's
see what happens the moment you do that
you can say there's no problem with name
so that means you can use a static
variable inside a static method but you
cannot use a non-static variable inside
a static method
the question is why I mean think about
this
brand and price they are instance
variable that means it will be different
for different objects now when you call
show with obj1 we know that in this show
when you're printing brand and price
you're talking about obj1
when you call show with object 2 you
know that the brand and price will be of
object 2. but then when you call
mobile.show1 how do we know which Which
object you are referring to so this
brand belongs to obj1 or it belongs to
visual two and that's why it says hey
there's a confusion right let's not do
that let's not have a non-static
variable directly getting access in a
static method it's not possible uh this
time I have added a directly keyword
that that means entirely is possible now
how would you do that indirectly it's
very simple what if you can actually
pass the object itself you can say hey I
want to run show one for obj object obj
one object now since you are passing the
object you have to also accept it here
so you can say mobile obj
and now now since we have the object I
can refer that with the help of obj1 dot
brand
so basically we cannot directly use a
non-static variable inside a static
method but if you have object reference
then you can use it because now we can
differentiate so the brand which I'm
talking about is for obj one not for
object two so that's how you have to do
it so that's how you work with static
method now if You observe here from
start we are using this right the main
method is static why in this world we
have a main static is because if you
don't make main static if this was a
syntax the problem is
if you don't mention static that that
means main becomes a non-static method
which means if you want to call Main we
have to first create the object of demo
oh that means you cannot call Main
without the object of demo but the
question is
we all know that main is a starting
point of execution if the execution has
not started how can you create object of
demo okay so there's a deadlock here
right uh so to solve that problem what
we can do is we can make this variable
as static so to solve that problem we
can make this main method as static the
moment you do that we are saying hey you
know to call Main we don't need object
of demo problem solved right so yeah
this is how we can solve this problem
and this is what static methods are
uh anything else I think it looks good
in the next video let's try to see
something more about static there's a
concept of static block let's talk about
encapsulation now I know that's a new
term but when we started with oops
concept now encapsulation is a part of
oops so when I say let's Implement
object oriented programming so yeah we
have talked about class we have talked
about objects and the next step is
encapsulation here now by word what
encapsulation means you know we have the
concept of capsules where we have
medicines powder there so basically we
can imagine capsule as something which
is keeping it close keeping it tight and
no one from the outside world can use it
that makes sense right so what we can do
here is let's say let's design a class
okay
and let's name this class as human I
know we can use different names but
let's go with human here and I know we
are aliens but let's say let's say this
is human now here when you have this
human class a human will have some
parameters right example uh if you
remember we have talked about this
before as a human or as a person we know
a lot of different stuff so in our mind
you have a lot of different concepts or
you know a lot of things example you
know your name you know your where you
stay you know your favorite actor you
know your favorite trainer of course you
can name you can use my name there but
just kidding so we have different
information right now can you imagine
this that all the information are
actually stored in your brain as a
variable box I'm a big fan of pixel
movie which is
I don't know the exact movie name but
you know uh Pac-Man basically eats
people and then they become pixels so
you can imagine the data in your mind is
Cube okay and in that box you have the
data example your name is stored in a
box which name Naveen or which names
name is equal to and in the Box we'll be
having a value for mates Naveen let's
say if you are your favorite actor so
you'll be having my favorite actor and
the Box Inside the Box will be having a
value so what I'm saying is all the data
is stored in your brain in the format of
boxes variables
now of course uh you can use these
variables right so let's say my name is
Naveen and let's say if I'm walking on a
street and if someone is asking my name
I might
provide my name what if someone is
asking my email address I might provide
them my email address depend upon who
that person is what if someone is asking
for my uh children's name my wife name
my family name my Facebook password no
I'm I'm not going to share those things
it's because there's something called
privacy right and yeah I know a lot of
people don't believe in privacy but of
course no one should be able to get your
data directly right it's not like your
data is available for the entire world
to see it's there it's closed no one can
see the data of course they can see my
Facebook profile but no one can see the
data inside your brain
that's important if they want to know
your data they have to ask and you can
decide do you want to share or not in
the same way let's say we have this
human class and in this human class we
have a variable called age and we have a
string which is named that's it just two
variables and now if I want to access
those data of course I have to create
object of human here and let's say this
is the human object Neo human and once
you got this object with this object you
can fetch data right uh of course you
can set the values as well and for this
particular object I can say obj dot h is
let's say 11. and obj Dot name is let's
say Naveen I know that's not my age but
at this point it's okay so we got these
values and we got this object created
here
now what I want to do is what if someone
asked me hey human or maybe someone is
trying to directly trying to fetch the
data example if I say s out and if I try
to say obj dot name now what we are
doing is just by using the object anyone
can fetch data okay and this will work
okay it will not give any issues I will
say compile and run you can see we are
able to fetch data and
syntactically there is no issue but then
if you really think that we have to
implement software for the physical
world or the real world it should match
with the real world not all the data are
directly accessible and we want to
control it so one way to do that is what
you can do is you can make your
variables private now what do you mean
by this private keyword of course we'll
have a detailed discussion later at this
point private simply means this
particular variable which is age is
accessible only in the same class let me
repeat this very this age variable is
accessible in the same class the moment
you make it private it's private no one
can no one from the outside world can
use it of course I can use my data
because that's private to me but you
can't access my data okay that's
probably to me right the same thing can
be done for the the invariable here and
if You observe the moment I do that we
got an error here I mean of course vs
code helps you that vs code says hey you
know this variable age is not visible
you know why it's not visible because
it's private now going forward this is
what you have to do every time you
create a instance variable let me repeat
every time you create a instance
variable make it private no one from the
outside world should be able to use it
now you will say hey that doing that we
are actually Breaking All the purpose of
building a software right if no one is
able to access this data then why we are
even creating these variables that's
right the reason why we're getting this
variable is because we can store values
and someone should be able to access
them
they should be able to access them but
not directly okay so there should be
some indirect way yeah we have indirect
way so the way they should be able to
access this data is with the help of
methods example let's say if you want to
know my name you have to ask for it and
I will decide should I should I share
the data with you or not so if you say
hey what's your name I will say okay I
will ask my brain what's my name because
most of the time I don't remember my own
name so I will say hey what's my name my
brain will say okay your name is Naveen
and then from my methods which is my
mouth or my by using my handwriting or
by typing somewhere there is a way I
have to share that data with you right I
have some methods Behavior I can talk I
can write I can type Now using those
behaviors I can share the information
okay not like anyone can just come to me
by it they will break my head and say
okay I got the data now that's not how
it how it should work so how do I come
how do I uh restrict it so what we can
do is we can make it private we are just
restricting it the only way to access
them is with the help of methods so what
I can do is temporarily I will just
comment these two sections and I will
assign the value here itself and we can
do that I will say name is Naveen and
then here coming back to public I will
say public I want to get data I want to
say hey get age okay and of course you
can use any method name it doesn't
matter but let's say get age and this
will return a integer value so I will
say int here and this will return so
this will basically return the age now
the question is can I access age here
and the answer is yes you can you can
access the age variable inside a method
of a same class that's right this get
age is defined in the same class that's
why you are able to access that and if
you see age here or name here so we are
trying to get the data of another class
demo and human there are two different
classes okay makes sense now now we can
also do it for the name so for the name
I will say public
string uh string get name and this will
basically return a name
okay so we got two methods get age and
get name and then we are returning the
age and name now if someone wants to
fetch it I can simply say Hey you know
don't call name that will not work
because name is a variable which is
private you can access the methods you
can say obj dot get name that's how you
can fetch a value of course you can also
fetch the age what I can do is I can
just say plus I can give a colon in
between and I can say obj dot get age
okay now I think we should be able to
access it let's try and compile
run oh it's working can you see that we
got Naveen and Levin so the point
remember is every time you create a
variable which is private we are making
sure that it is restricted no one from
the outside world should be able to use
it so this age variable this name
variable will be used by their own
methods that actually makes some sense
okay but there is one little problem
here what if I want to assign the value
what if I don't specify the value here
cut and cut let's say we have the
variables but don't I don't assign the
value now of course by if you don't
assign the value default value will be 0
and a null string but I want to how do I
set the value now for getting the data
we have said get for setting data can we
say set let's try so here for age I will
say public now when you're setting the
value you are not getting in return
something right so you will say void and
you will say set age okay now it's just
that when you are setting the age you
have to ask hey what is the value so
maybe you can also accept a value here
maybe I can say a right and then here I
can say age is equal to a now what I
mean by that is of course you have a
method which is accepting a value
assigning that to age but how it will
work so let's come back here which the
the portion which we have commented I
want to set the age right so instead of
setting the age to the variable I can
say obj dot set age we are using a
method now not the variable and in this
particular bracket you can pass the
argument and let's say the age is 30. so
now we are passing the value now this
value will be assigned to this a and
from a a this will be assigned to age
can we do the same thing for string
let's try I will say public void sect
name and of course we have to also
accept the name but what's the format of
a format of name it is string name I
will say end this time and here I can
say name is equal to n so whatever value
you pass will be assigned to This n and
from n it will be assigned to name now
the same thing need to be changed here
so I will just cut this part and I will
say cut this part as well I will say set
name and in the double quotes I will
pass the name
and the name here is Naveen
and we will use a different name this
time I will set a d okay and now I will
just come back here clear the screen
compile Run Okay so that we got ready
and study so what we are doing is we are
assigning the value with the help of
methods here and we are getting the
value with the help of methods here
so that's how we can access this data
now what we are doing is we are making
your variable private and then the only
way to access them is with the help of
methods right so basically we are
binding our data with the methods the
only way to access that data is with
methods so no one from the outside world
can use your variables directly so
somewhere we are encapsulating the data
and methods and that is encapsulation
okay simple stuff right uh so yeah
that's it from this video let's try to
understand this more what is this get
and set methods uh can we use different
names or
only this name will work that we'll
discuss let's try to understand what
these methods are or can we change the
name say get Aid set age makes sense but
can we use some other names actually we
can instead of saying get age we can say
let's say we can say ABC and set age we
can say x y z we can do that okay there
is no harm in that the only thing is
when you call this methods of course you
have to change the name I will say this
is XYZ so when you set the value you
have to call XYZ and then when you fetch
the value you have to say ABC and it
surely works if I uh try to compile this
and run you can see it works now the
problem with ABC and XYZ or any name is
your method name should Define what user
what is your intention because most of
the time it's not just about writing
code it's also about reading code when
you write a code once it will be read by
multiple people in the entire lifetime
of a software why not use proper words
which explains what that method is doing
so instead of saying ABC if I say get
age each it is actually makes sense
right it is much more readable what
you're doing there right and as I
mentioned before it is not a compulsion
to use the same name but then as a
developer we have adopted this standard
whenever you want to get the value of a
variable the method name would be get
Space the other variable name the
variable name which is age to set the
value you will say set and you will use
the variable name which is age okay so
that's how we can use this so This is
called a getter so for the variable user
this is a getter and to when you want to
set the value so the method is called
Setter so we can say that's those are
Getters and Setters uh in fact the
beauty is if I delete the entire part
okay let me just do that I know we are
we need to type that once again actually
you don't most of the ideas have this
amazing feature you can just right click
and there's an option of source in fact
it doesn't matter which ID you are using
uh you will see the option of source or
insert code something like this so it
will say source action what do you want
you want to get you you have to say
generate Getters and suggest for me
click on that for both the variables and
click on OK you can say it will generate
the methods for you and you see that
variable names it's same get age set age
and then we got get name set name okay
and those are called Getters and Setters
and of course there is no compulsion to
have both the methods you can also you
can only have get name you don't want to
have set name that's your choice there's
no compassion that there should be both
it depends upon you how you want to
implement it for this example I want to
assign value to H name I want to get the
values as well and that's why I'm using
this show so only thing is for every
variable you need two methods Getters
and Setters okay so yeah that's it uh
but there's only one issue now if I use
the code which is given by the IDE you
can see this new keyword here we got
this in this video let's talk about this
because in the previous video we were
doing something and then suddenly we got
this keyword so it's important now to
talk about this keyword here now what I
will do is I will just remove this or
I'll just change this variable name back
to A and N and of course here we have to
say A and N right and let me remove this
this keyword from here just to see if
this works now if I remove this keyword
from there and you find on this code
compile okay there is some problem with
the variable names I think we are still
calling x y z so it should be set age
and we are still calling ABC it should
be get H the same thing which we have
done in the previous video
okay so if I save this and if I go back
and compile so compile done
running
done so you can see we got the values
right the thing is when you talk about
this variable like age and when you're
passing a here we are using two
different variables right
now the point to remember here is this a
variable here is a local variable this
age variable here is a instance variable
right if you want to understand that
with a diagram uh you can just go back
here we have a stack memory remember we
have talked about stack and Heap so we
got a stack here and then we got Heap
here now the moment you create the human
object we got this object here human so
in this we have a human object and of
course it will have some address let's
say one zero one so we got obj and the
address is 101 that's the first object
we got and there is a link here which we
can cannot ignore and then we have some
more variables you can see if you
execute and of course this was my main
stack uh now we have executing
which method so if you say set age we
are executing set age method right
Now set age will have its own stack here
let's say we have a set age stack here
you know what I just have to zoom it a
bit
and here let me create segments so we
got multiple segments here and of course
this will be linked with uh this
particular variable here and don't you
think this this box which is address
once the one is an object of human so it
will also have the instance variable how
many instance variable we have we have
age and name so we got age and we got
name here now if you look at the set Age
Now set age this particular stack uh is
of set age every method will have its
own stack and in this we got a variable
called a and the value for a which we
are passing is study so we got 30 here
okay and then the same value 30 we are
assigning to age that means we are
changing this variable and we are
assigning a value which is study there
if that makes sense okay so both the
value for a and age study and that's why
when you fetch data when you say get age
it will return the value of age in the
object
which is study in this case and that is
perfectly working
now the problem is what if I just make
this particular variable age as age I
mean a as h
now what I want is I want my local
variable and my instance variable both
to have the same variable name
what do you mean by that is if I remove
this a from here the variable name here
will be H so both the variable name the
local variable and the instance variable
have the same name
then it should work right what we are
trying to do is the age variable will
get 30 here so of course in this stack
we got 30 and if you see we are
assigning H is equal to age so I'm
expecting that this age will get the
value from this particular age it should
work right let's try if I go back to my
code and compile and run
oh can you see that the value for age is
still zero that means the assignment
which we are assuming that it will be 30
it is still zero why
the reason is
if you look at line number 11. and if
you see it we are saying age is equal to
age
the problem is by default now see this
age can be local variable this age can
be instance variable
right because the names are same so can
we do this can we say it is possible
that
the age here is actually a local
variable it is also possible that the
age is assigning value to itself
maybe this age is not even an instance
variable that means this age is
assigning value to itself and this age
here
which we have created it is still
zero and that's why we are getting 0.
how do we solve this problem so
somewhere we have to mention hey you
know this particular age here is not a
instance variable this is not a local
variable this is an instance variable so
remember this point the preference will
always give always be given to local
variable so in case of confusion it is
always the local variable we have to
mention by some way hey this is not
local variable that's an instance
variable
how do you mention that so in order to
say that's an instance variable can we
do this can we say
a human can we get object here itself
object one equal to new human and then
we can say obj1 dot h now what we are
doing is we are saying this age is a
instance variable and you might be
thinking hey how can we use age with a
object see we can do that because we're
in the same class okay we were not able
to do that here because we were in
different class but again the problem is
we are saying this age is instance and
this age is local this should work let's
see if this is a problem or we have
solved the problem let's run this oh it
is still zero what is happening let's
try to understand more now when you
execute this set age method what we are
doing is we are creating a new object oh
that's the issue we are basically
creating a new object okay
um how do you solve this problem we
don't want to get new object because the
moment you create new object what will
happen here is it will create a new
object let's say 103 and this will have
this will also have age equal to name
equal to and what value you are signing
here your assigning value which study
and then here in this set age you will
create obj1 which will have the address
103 and there's a link here
so the value which you are changing is
of this age not this one we want to
assign the value to this particular age
that means creating a new object is not
a good idea okay how do I clear this
let's remove this
in fact you know this is a problem this
is creating a new object
okay if I don't want to get a new object
how do I access
this obj oh I got an idea here what if
with this 30 if I can pass the object
itself can we will it solve the problem
with 30 if you can pass this particular
object and we can accept the object here
what type of object it is it is human
human obj
and then here we can simply assign the
value so what I'm doing is if you if you
observe correctly we are not creating a
new object we are basically passing the
reference of the old object
so here it will be not 1 0 3 it will be
1 0 1. okay so this obj1 here will get
the address 1 0 1 and we can simply say
obj1.h and now we are not referring to
this address we are referring to this
address so we can change the age value
30 and let's see if this works I hope
this will work compile sorry compile
run oh it is working it's working so
basically the important thing is how do
I differentiate between a instance
variable and a local variable is by
passing the object itself but there is
one little problem here the problem is
if you if you read this line it says obj
dot set age and then you're passing the
object of the obj object as well why we
have to do this why you have to mention
obj two times
knows this Java says hey you don't worry
why you have to pass the object two
times I mean you're calling the method
by using the object you're also passing
the object don't do that don't pass the
object by default I will give you this
obj you don't even have to accept this
object what if Java says hey don't worry
don't create the object don't pass the
object I will give you the object and
that object my friend in fact you know
when we had a human here we don't even
need this human line here we could have
removed that and even obj would have
worked so your Jawa says hey why do you
even use this obj we can when we can
simply use this now this is a keyword
which represents the current object now
when I say current object what it means
the object which is calling the method
set H is called by obj which is this
object
here in this method we can actually use
that object with the help of this
keyword so this refers to the current
object who is calling the set set age I
hope that makes sense so from this point
we are always going to use this which
represents the current object
okay so here as well instead of using
name or N I should have used name the
only thing is we have to refer the first
name here is this dot name which is the
object itself the current object I hope
uh this all this thing have made sense
this is what this keyword is in this
video we'll talk about Constructors now
what are Constructors now look at this
example here which is of human now when
you talk about human we have some
variables right of course when you talk
about these two variables these are
instance variable and then we have seen
in the image as well uh basically
whenever you create an object example in
this we are just creating one object and
that object is getting created inside
the Heap memory you can see this is the
object we got
and of course with that object we have
assigned the value for the age we have
assigned the value for the name as well
which which is ready but I have not
written it here but we know that the
object is created
now the thing is
when you create the object if You
observe the line number 29 on this line
when you create the object what happens
when you create the object in the hip
memory it will just create a blank
object example if I try to remove this
if I keep it empty it will create a
object with a value so the value would
be I mean it will have a variable which
is age and the value will be 0 and it
will have a variable called name and the
value will be null right I will just I
will just try to print those things uh
what if I do is I will just print the
same statement before assigning the
value
right so I'm printing it here and I will
comment this section so that's how you
comment right I don't want this line to
be executed and now if I go back here
and compile
and run you can see we got null null
basically is
when you don't have the data assigned to
object type that's right string is an
object type I will discuss about string
later in detail as of now just remember
by default the the value font string is
null and the default value for integer
is zero okay that means if you don't
assign these values there will be
default values what I want here is of
course there is a way you can assign the
values later but what if I want to
assign the value when the object is
created
that's right on this line itself I want
to assign the value that means the
moment I get the object I don't want to
have a null value I want to have some
default values example let's say by
default every object created the name
should be something else the name should
be let's say Babu or something else I'm
not sure but can we have a default name
can we have a default age so let's say
for my application uh this application
can be used only by those people who are
12 and above so I can simply say hey the
minimum age for this is 12 so by default
the value for the age should be 12. can
we do that
so how do we achieve that of course we
can assign the values here or we can use
something called a Constructor now how a
Constructor looks like so a Constructor
looks like a method itself let me repeat
a Constructor looks like a method itself
that means a Constructor will have a
name a Constructor will have the round
packets example if we talk about methods
here we have a name and we have a round
bracket in the same way for the
Constructor as well we have to use that
so what I will do is I will say public
now the only changes in the Constructor
you don't specify the written type okay
so we can directly mention the customer
name here but what should be my
Constructor name now there's a
compulsion that your Constructor name
should be same as your class name so
Michael what is my class name it's human
and then since it looks like a method we
can give a round bracket and we can open
and close the curly brackets now one
thing I wanted to mention you can see
with the cuddly packets are mentioned
just I mean for the opening brackets are
just mentioned on the same line and here
the curry packets are mentioned on the
new line both Works Some people prefer
to use on the same line Some people
prefer to use on next line so anything
works now in this Constructor I can
assign the values but at this point
let's not assign the value I will just
simply print the statement I will say s
out and here I will print in Constructor
so you can see we are printing in
Constructor here so that's our
Constructor okay so let me repeat what
is Constructor instructor is a special
method that's why because it looks like
a method it has the same name as a class
name so those are the rules you have to
remember the Constructor will have the
same name as a class name a Constructor
never returns anything so don't don't
have to mention ain't float or doing
anything there so just specify the
access which is public and then mention
the name which is human
and in this you can do whatever you want
okay so I'm just printing in Constructor
so let me just try and compile so
comparison done there is no problem
code one thing to observe nowhere see
when you talk about this methods like
get age or set age all these methods we
have called them right so this is where
you are calling them
Constructor you can see we are not
calling it but still Constructor will be
called
okay so even if you don't call it it
will be called now when it will be
called every time you create an object
it will call the Constructor so every
time you create the object it will call
the Constructor example let's say if I
create two objects I will just copy this
line and paste it here of course I
should have a different name for the
reference obj1 now you can see we have
two objects now when you say you have
two objects and if I try to compile and
run this
you can see we got in Constructor two
times so every time you create a new
object it will create a Constructor or
it will call the Constructor okay if
that makes sense uh what we can do is if
we can remove this line and I can assign
the values I can say age is equal to 12
and name is equal to let's say by
default John of course you can have any
name but let's say John
now in this case I can see if this if
these values are assigned what I can
also do is I can just comment this
section let's say I'm not assigning the
values let's see what are the default
values compiled one you can see we got
John and 12. so by default
you assign this value okay so this is
where Constructors are helpful now you
might be thinking hey we can assign the
values here itself right uh see there's
a idea there's a standards which we
follow whenever you want to perform any
operation always do that in a method
don't openly do it in the statement like
here if you want to perform some
operations like assignment or
calculation always doing the methods and
Constructor is like method right so you
can assign the values here there is no
harm in terms of compilation you can
assign the values here as well but we
have to follow standards right and also
just try to think about something
Advanced let's say you are trying to
connect with the database now in that
scenario your application is trying to
connect with a database or the network
you need that connection right now where
you would like the connection
you can write the connections in the
Constructor
and that's why this becomes very
important now if you remember we have
also talked about method overloading so
when you have two methods with the same
name but different parameters those are
called method overloading now can we do
that in Constructor that's tricky right
okay so now we know what is constructed
right but what about this I mean can I
pass the values here what if I don't
want to assign values like 12 and John
what if I want to customize it so what I
want is every time I create the object I
should have an option of passing those
values not 12 and John every time can we
do that of course you can assign the
values later with the help of set
methods but what if I have an idea where
hey you know I okay let's let's go with
this object as well the second object
and in the second object I want to pass
the values the first object I want it to
be default the second object I want the
age to be let's say 18 and the name
should be let's say Naveen can we do
that if you can see this line is giving
you error it says hey you know you don't
have a Constructor which accepts two
values so those two values of type
integer and string you don't have it and
if you go up actually you don't have it
you don't have a Constructor which takes
two parameters can we do that let's try
so I will say public
human and I want this human to take two
parameters so I will say int
a comma string name and then here I can
just come back and I can say age is
equal to a so not the default value
which I want to assign here I want to
assign the value which is sent by the
main method so if you can see we are
passing 18 and Naveen here right so I
can just go back here and H is equal to
a name is equal to n now if you look at
this particular Constructor here it is
taking some parameter so this
Constructor is called a parameterized
Constructor oh I should say this is n
now what is the difference between
normal Constructor and a parameterized
Constructor is in fact it's normal
constraint is also called a default
Constructor
now we'll discuss why this caused
default Constructor so this is called a
default Constructor this is called a
parameterized Constructor because we
have parameters there and whatever value
you pass here will be assigned now you
can use both syntax you can either
create an object by not specifying any
parameter or arguments and you can
create a object with the help of values
which we are passing it here so this is
parameter wise and this is default now
what I will do just to explain this is I
will just copy the same line and I will
print the values for obj1 this time not
for obj obj one so basically we are
printing both and let's see what's the
output is compile run you can see we got
the first object drawn 12. the second
object is not John and 12 which is
Naveen and 18 because you are passing
those values now what I will do is
timeline I will remove this part just to
explain you something
see when I mentioned that every time let
me just comment this section as well see
every time you create the object it will
call the Constructor right but then if
you see I have removed the Constructor
will this work and it was working before
remember when we started this example of
human we were not having any Constructor
it was still working
at this point your Java will say hey
don't worry if you don't mention
Constructor there I will create a
Constructor for you and that's why we
say that's a default Constructor so
behind the scene you will get this
Constructor here which is public human
this is what you will get even if you
don't mention okay the only thing is it
will be default it will be blank if you
don't mention but if you want to do
something of course you have to mention
that explicitly and we can use the same
code or I can actually ask my IDE to
give me the code so you can simply go to
source and action and you can say hey I
want to create a Constructor but which
Constructor so I want a Constructor
which takes both these arguments and I
also want a default Constructor
Source action I want a Constructor which
is default you can say we got two
Constructors
there's only one change the syntax which
we have returned was a and name and here
if you can see we have age and name
and to make it work we have to use this
keyword I hope to remember this keyword
video previously and that's how it works
it has the same way which works the only
thing is we have to assign the values
here I would say age is equal to 12 and
the name is John so that's how we can
basically use a default Constructor and
a parameter-wise Constructor of course
we can create some more consider here
what if you want to just specify the
name not the roll number so you can say
I want a Constructor
Source action
and I want a Constructor which takes
only name so you can you can say we got
a Constructor which only takes a name
now what happens to this type of objects
example if I create an object here let's
say the second object and this time I'm
not passing two values I'm just passing
one value which is name in this case the
age will be zero so what you can do is
even if you're accepting name you can
assign the age by your certificates at
12. you can say age because there is no
confusion or you can also say this dot h
just to maintain the uniformity okay uh
so that's how we use Constructors
default Constructors parameterized
Constructors in this video let's talk
about this and super now this is a very
super concept so let's focus so what I
will do is I'll just remove all this
thing just to make it simple and clear
this part as well and for this I don't
even need uh this particular classes so
let's let me just close these files and
keep it simple okay so we have
everything very simple code here now
what I will do is just to understand
this and super I will create a class
called a I know this is a very simple
name but just for the example we can
take them and then we got a class B
okay we got two classes and then I'm
also saying that this B Class extends a
of course we are doing an hat and CR and
it makes sense because we just talked
about inheritance and then what I will
do is I will create a Constructor for
both of course we can do that right now
before creating Constructor let me say
if I create object of B of course we can
do that right so this B Class we call an
object of B Class here and we can do
that let me create a Constructor of B
here now how do we get a Constructor
it's very simple you specify public and
then you say B back it open and then
here I will type in B I'm just trying to
keep it as simple as possible that's why
we have taken Class A and B and then a
very simple statement now what I will do
is I will try to compile this code and
you tell me what will be the output
comparison done right if I run this code
there will be some output right now
think about this we are creating the
object of B okay we are instantiating it
and we have learned about this that
whenever you create the object it will
call the Constructor of a class so the
object we are getting is a b and we have
a Constructor which is B here which is
which prints a statement so of course
I'm expecting that it will execute the
Constructor and it will and you that's
why you got in B that perfectly makes
sense and we have talked about this for
a long time
The Twist here is what if I have a
Constructor in a as well and here I am
printing in a now what do you think will
be the output
because of course we are creating the
object of B not a so it should call the
Constructor of B and that makes sense
but if you compile this code you will
see something strange if I compile this
code and run oh it is also executing the
Constructor of a now that's weird for us
right because we are creating object of
B it should only call the constitution
of B
but it is also calling the Constructor
of a and that sounds weird
now we'll understand that but at this
point just remember whenever you get
object of a class it will call the
Constructor of subclass and superclass
both a is a superclass here B is a plus
it will call the Constructor of both why
we'll talk about it in some time but it
calls the constitute of both now let me
just add a Twist here in B let me create
a parameterized Constructor and we have
seen that right so what is parameters
Constructor a Constructor which takes a
value let's say this is n okay and here
I will print
in B int because we have a Constructor
which takes a integer parameter I'm just
printing e just in just to differentiate
between these two statements now with
this if I compile this code and run what
do you think what will be the output
compile and run still it is in a and in
B why not in B int is because when you
are creating the object you are not
passing any value here basically you are
calling a default Constructor but if you
pass a value let's say 5 in this case
you are specifically mentioning hey you
know I'm creating an object of B and I'm
passing a integer here so it will call
the Constructor of B which takes integer
Now by doing this if I run this code or
you can see it is printing in a and in B
int okay that actually makes sense it
will call the concept of a but what if I
also have a parameterized Constructor in
a as well which takes a n and it also
planes in a end now since we were not
having a parameters Constructor it was
calling a default Constructor that's
what I'm assuming at this point now when
you have a parameterized Constructor for
both for A and B both
now there is an expectation that it will
print in a int and in B int and that's
what I'm thinking I'm not sure what
you're thinking uh let's drive let's see
if this works oh no
what is happening here it is calling the
parameters constitute of B that actually
makes sense but why the default concept
of a it should have been called this
this one right let's understand why it
is first of all Calling The Constructor
of parent class why in the first place
the thing is and remember this point
every Constructor in Java
has a method
which is there even if you don't mention
okay and that method is super
now this method is there even if you
don't mention you can imagine that's
like a John Cena I don't know if you
know the John Cena memes but that's just
that you can't say it okay so super is
there you can't say it even if you don't
mention super it is there so by default
every Constructor the first statement is
super
and every Constructor not just this one
every Constructor here as well super
okay so every Constructor will have
super same goes for a as well it will
also have super
and super irrespective which class it is
it will have this statement super even
if you don't mention it is there okay
that's a point to remember now let's try
to understand how it is working let's do
a dry run the moment you execute this
statement what is happening it is
calling the Constructor of B which is
parameterized so it is calling this
particular method so when you execute
this method the first thing it sees is
super not the system.out.pental N what
it is saying is super now what is super
now super method simply means call The
Constructor of a superclass so let me
repeat super means call The Constructor
of a superclass now watch this
superclass this is a superclass it is
calling the Constructor of a superclass
but but which one the parameterized one
so the default one if you can see we are
saying default we are not passing any
parameter here so just calling this
particular Constructor and that's what
is printing in a and that's why if you
can see the output it is print first
printing in a and then once it executes
the a Constructor it will execute the
remaining part of B Constructor which is
this part in B int and that's why we got
in Bay end okay that means if I don't
want to call this Constructor if I want
to call the parameter wise one we have
to do only one change which is what if
in this super you pass a number so N is
a value right it will have a value the
same value you are passing to this super
now what we are saying is hey Java I
know you are going to execute this super
glass Constructor but I am passing a
parameter there so now this time you
have to call the parameterized
Constructor by doing those changes let's
compile and run here we go it is
printing in a int and in Bay end so
super is a very handy tool it's there
already you don't have to mention that
but if you want to make some changes of
course possible may you have to mention
so if you want to pass a parameterized
Constructor then explicitly you have to
mention super I hope that made some
sense okay now what I want is I want to
call the default Constructor of B okay
I'm not passing any parameter here I'm
calling a default of B
so of course if I execute this
if I compile and run you can see it's
printing in a and in B why is because
when you are calling the default
Constructor here in default concept of B
it will execute first it is calling this
super that means it is calling this
middle Constructor which is printing in
a and then it is printing in B it will
continue with this execution of consider
B right but what I want now is I know
you got the point what I want is I want
to execute in a int and then I want to
print in B so the output which I want is
in a INT in B so how can we play with
that so what if here if I pass a value
let's say 5 or any number doesn't matter
if I pass a number it will try to create
object of B with a default Constructor
it will execute the default Constructor
but now we are calling a superclass
Constructor by passing a value
so which one which computer will be
called of course the second one and it
will print in a INT in B let's try
compile run and that's what we got so
that's how we can play with super and
that is fun right now I have a question
for you maybe you have observed it or
not see in B Class when we are saying
super it actually makes sense because we
have a super class for B okay this is a
here is a superclass but when you say
super for a what is a super class for a
we have not mentioned anything here
right okay now that's why you have to
introduce A New Concept here every class
in Java that repeat every class in Java
extends the object class
so object is a class in Java which has a
lot of methods we'll talk about those
methods later but every class in Java
extends this class even if you don't
mention so even if you don't mention
this it is extending it again you can
imagine this as a John Cena it's there
you can't see it okay so even if you
don't mention or you mention it's the
same thing
So when you say super here you're
basically calling a Constructor of the
object class
okay an object class also we have a
Constructor this is what you are calling
cool right uh so even if you don't
mention it is there now you might be
thinking the b class must be extending a
and object both no B Class extends a a
class extends object so this is
multi-level inheritance okay there is no
multiple still now okay so yeah that's
how it works we have object class so
with this super represents the
Constructor of the object class so yeah
so we have talked about super but what
is this okay now let me introduce this
here the output which I want now is I
want to execute both the Constructor of
B okay so let me just keep it default
now let me say super I want to execute
both the Constructor of B so I want only
one object okay with one object can I
execute both the Constructor of course I
want to execute the Constructor of a
which is default but I want to execute
the Constructor of both P so what I'm
saying is
I want in a I want in B and in B int is
it possible uh for that what we can do
is see we are creating the Constructor
let me pass a value here let me pass 5.
so of course by doing that what we are
doing is we are calling the Constructor
which is the parameterized one
and we are calling super and that's what
he's calling the superclass Constructor
but then we have one more method called
this we have talked about this keyword
right now what this this will do is this
will execute the construct of a same
class let me repeat this will execute
the Constructor of a same class which is
this one we are not passing in a
parameter so it will call the construct
of a same class and then this
Constructor is calling the construct of
a superclass
let's try if this works compile run and
you can see that we got in a in B in B
int I mean of course this will execute
first this method but this method this
particular method B Constructor is
executing this which is the default
Constructor the default Constructor
executes the super which goes here it
will execute in a it will execute in B
and then in Bay end
so that's what is which is this keyword
and also this method and super method so
this method execute the constitute of
the same class super method executes the
construct of a super class in this video
let's talk about the naming conventions
now if you see the code which we have
written till now somewhere I was using
capital letters I was using small
letters when to use what
and then what if you want to join two
words how will you make it more readable
now that's where Java says it follows a
naming Convention of camel casing so
basically it uses
camel casing now what camera kissing
means or let's talk about in general how
do we name our classes now whenever you
create a Class A Class name should start
with a capital letter so when you talk
about class it should start with a
capital letter example if you want to
get a class called calculator the C
should be Capital now on the other hand
if you talk about variables or methods
so for variable and methods what you
will follow is you will start with a
small letter example if your variable
name can be marks a variable method name
can be show so it will always start with
small class capital
variable method small in fact we also
have a concept of interfaces which we'll
discuss later so if we talk about
classes and interface we'll have to make
it capital let's say interface is
runnable so basically this is the
convention which which we follow class
interface we have capital letters
variable methods we have small letters
we also have a concept of constants
which we have talked about uh so when
you talk about constants it will have a
capital but all capital example if we
talk about the value of pi if we talk
about a constant of brand so it doesn't
matter what your constant is so you can
have all capital here now why do we do
this we do this just to see and
understand what could be the thing which
you are doing example if you say if you
see this type of things you can guess
hey it can be a class or interface if
you look at this you know this is a very
this is a variable if you look at this
you know this is a method and we look at
this this you know these are these are
constants it makes your code much more
readable and that's important modern
right it's very easy to write a code
which works it's difficult to write a
code which anyone can read and that's
why you should follow this convention so
this is how you use the main convention
but what if you have a word which which
has two letters example if you talk
about show my marks if I want to do this
so you have to say show my mark because
if you say show my marks it is actually
a bit difficult to read right so what
you can do is every time you combine
words make sure that the first step of
the second word or the first letter make
it capital it makes it much more
readable compared to small letters now
this is what camel kissing means you
know we have camel so it goes up and
down so we have small letters then we
have in between we have Capital small
again we have Capital so this is camel
casing now apart from this there are
different languages which follow snake
casing rule where we use underscores
example in some languages they follow
snake casing they use underscore and
people who jump between different
languages they get this tendency of
using underscore so again Java will not
give you any error but if you follow the
Java pattern Java developers will not
like this so if you're writing a code
where you have a Java team or everyone
that works on Java try to follow camel
casing and but again it will not give
you either it perfectly Works underscore
works in the names but that's what we
follow we follow camera guessing here
not snake casing yeah uh if you have the
class name which is
again uh I want to say my data is a
class so you can say m is capital
because that's a class name now I will
give you I will show you some names and
you have to guess what those are example
if I say h
that's variable right okay what if I say
data what is this this is a constant
because everything is capital
okay uh yeah in in terms of constant if
you want to say my data which is a
constant you have to use my data but
again everything is capital right so at
this point you can use underscore just
to differentiate this and again these
are the good practices which I'm showing
you how about this if I use something
like human but I use a round bracket any
guess yeah that's a Constructor why is a
Constructor is because the first is
capital that means it represents a class
name and we also have a round packet
method like something so that's a
Constructor so this is a naming
convention which we follow and try to
use good names for your variables your
classes your methods so that it will be
easy for others to read okay so now we
know how to create the object right so
we have a class let's say we have a
class A and then in this class A we have
a show method now how do we call show
method that's very simple first you have
to create the object of a and then you
can call the show method now what
happens behind the scene so of course uh
you have your big jvm here and then in
this you will be having your stack
memory and then you'll be be having your
hip area as well now in this Heap memory
so if you look at line number 14 it will
create an object let's say the address
is 1 0 1 and then in this you will be
having a variable or methods we don't
have a variable as of now so let's say
we have a method we just show so of
course in order to call this show we
need object so we have done that and
then we have obj here the address will
be 1 0 1 and it will refer here
and then every time you want to call
show basically you have to say obj dot
show that's how it works right okay now
just to clear the things this obj here
is not called the object it is called a
reference variable right so this is your
reference variable what is called a
reference variable because it is
referring to an object the object is
here so this is your object
okay so the question is if I want to
create this object is this line
compulsory or do we have a shortcut now
to understand this mode Let's also use a
concept of Constructor so let's say we
have a Constructor here which is a and
then I'm just trying to print something
here it says object created so of course
we know every time you create the object
it will call the Constructor as well so
it should print so if I compile and run
this code you can see it says object
created and it is printing in a show now
actually if you look at this line here
there are two steps not one example so
let's say if you create a local variable
called marks okay and then you set the
marks for it you set the value for it
let's say 99
we had everyone hates this type of
people right anyway so we have this
variable so what we are doing is we are
first of all declaring the variable and
then we are as a value the same thing
can be done
you can do it in two two steps we can
declare the object and then we can say
obj equal to new a
now this is called reference creation
right this is where you're creating a
reference and then this is where you are
creating an object and assigning the
value to obj
that means this is I mean when you say
new a this is where you create the
object let me show that let me remove
everything from here and say new a this
is object creation not the entire line
when you say new a Constructor that is
your object creation the moment you do
that in your hip memory of course we
don't have all this data now so ignore
all this data which is which is there
let me just remove this this is not
there imagine there is no object so this
line will create an object doesn't
matter what's the address let's say 501
and it will have this show method okay
the only thing is we are not doing
anything we are not creating any
variable inside stack example when you
say ain't marks the moment you do that
it will create a int variable called
Marks here the value will be the value
will be blank and whatever value you
want to assign you can assign that here
but if you can see we are not doing
anything here we are just creating a
object that is created inside the Heap
memory nothing in static and if you
don't trust me let me just show you the
proof If I compile this code and run it
says object created this is the object
and this type of objects are called
Anonymous object you know why it's
because this type of object don't have a
name right what do you call when you
have a reference it is called a
referenced object okay because there is
a reference in this tag so when you say
obj there's a reference here for the
anonymous object there is no reference
the only problem with this type of
object is you can't reuse them once you
have written this line you got the new
object in the Heap how will you use it
that's the problem right so you should
use this object only when it is required
so let's say if you want to call show
you can actually call this okay so you
can say new a
dot show this is object right this is
object so using the object you can call
show the only thing is you can't use the
same object again
so if I compile and run it worked the
only thing is you can't use this object
once more so if you write this line once
more what will happen now I mentioned
that you can't reuse it what happens
when you do that you can see it says
object created so it has created two
objects every time you say new a it
creates a new object so whenever you
want to use a normal object you can use
this of objects now let's talk more
about oops concept now oops basically
stands for object oriented programming
now in object-oriented programming we
have talked about object class
encapsulation right now let's talk more
the concepts now one of the most
important thing in the concept of Ops is
called inheritance now what is
inheritance now there are two words
actually here which which will confuse
people is is and has now what these two
words are now if we talk about a
computer now of course computer itself
is abstract concept right now A a
computer can be a laptop a computer can
be a desktop a computer can be a mobile
phone that's right so even if you talk
about this phone this is a computer in
the form of mobile phone of course and
the computer itself is an abstract
concept no one owns a computer you
basically buy a hardware which can be a
desktop laptop or a phone now can I say
that if you talk about a desktop so I'm
talking about the desktop which is this
big and it will have certain parts right
a desktop will have a motherboard a
desktop will have a hard drive CPU Ram
so when you talk about this thing it is
desktop has a motherboard desktop has a
hard drive it has a CPU right so the
important keyword there is has if we
talk about her house a house will have a
TV a house will have a sofa AC bed so
all those things what a house has right
so house is an important word but at
this point let's not focus on has in
this video let's talk about is now what
is is okay so example if you talk about
a laptop so can we say a laptop is a a
computer so what it means is laptop got
it features from a computer so can we
take another example here if we talk
about a car let's say let's say if you
talk about a Fortuner which is very
famous in India so this car is actually
a car right so Fortuner is a car so
that's how you represent something you
represent a device or a physical entity
by referring to its upper model right
you try to take the features of it now
coming back to the enhance Concept in
real world example let's say if we talk
about the human world you know when I
was in my 10th standard so just for the
example okay nothing not that important
but when I was in my 10 standard I did
my 10th in 2005. at that point Nokia
released a lot of smartphones right of
course Nokia is not there anymore but
Nokia was one of the most important
factor in the smartphone industry now
when they came up with a smartphone one
of the most famous smartphone which they
built is double six double zero I'm not
sure if you have seen that I'm not even
sure if that you're that old maybe you
were not even born in that year but but
yeah so it was double six double zero uh
amazing phone if you can just search on
Google uh Nokia depositor double zero
you will see that phone now a lot of my
friends were having that phone it was
costly phone at that point it was around
10 000 rupees and I was not having any
phones so they used to ask me hey which
phone you have I used to say hey I don't
have a phone but then I realized hey
till when I will say that uh the thing
is next time when people used to ask me
which phone I have I used to say I have
double three one zero now I was not
having a new phone now this is my
father's phone and we know the concept
right father's phone is ears phone in
fact in in general when we say our
parents property it's your property
whatever they own it's yours I don't
believe in that okay I'm not a big fan
of inheritance on nepotism but yeah you
get everything uh so I used to say I
have that phone okay so this is it
heightens now how will you use this
concept in programming now in Java what
you have is you have different classes
right example if you create a Simba
class here and let me get a very simple
class let's say we have a class here
called a calculator now what features a
calculator will have a calculator will
have some variables here and then it
will have some methods let's say method
is ADD method is sub okay and then
method is multi so we have different
methods here or let's also have division
why division should be the left there so
we have all these methods right and it
is working so you can basically create
object of calculator and you can access
all these methods no harm in that but
what if you want to create a advanced
calculator now of course let's say uh if
someone comes to you and say hey you
know you made an awesome calculator and
now I want you to create a scientific
calculator or advanced calculator now
you have a choice you can edit the same
class but there's only one thing what if
you enhance the same class you add some
more methods here now you want to give
calculator to someone someone asking you
for the calculator object they basically
access all the basic features and
advanced features as well
so it is good to create a submit class
okay so you can get a separate class and
you can say advanced calculator right
and then this will have all the advanced
features of course it will have all the
basic features and it will have the
advanced features as well so we have
basic features Advanced features both
but don't you think you need to Define
these basic features again and again why
we already have those features here
right we already have those features
here can I just use those features in my
new advanced calculator
so what I'm saying is basically this
advanced calculator is going to inherit
the properties and features from
calculator so I can also say Advanced
character is a calculator and it will
get all the features of calculator okay
uh it will make much more sense once
once we start coding but what we are
doing here is we are doing inheritance
so basically inheritance is a very
important feature using which you can
just copy the feature from the upper
class so this is your can you can I say
this is a parent class so this is a
pattern class and this is a child class
because child class is accessing the
feature of parent class okay so whatever
I earn it's my money plus my parents
money is my money that's how the system
works right we can also say this is a
super class we have different words for
it that's it and we can say this is a
subclass we can also say this is a base
class not your base and this is a
derived class so it depends upon how you
represent that if you say this is a
parent class then you have to say it's a
child class if you say that's a super
class then it becomes a subclass if you
say this is a base class you have to say
this is a derived class that's how it
works okay now this is what inheritance
is so in theory we have talked about
what is an Essence right basically you
can just use the features of a
superclass let's try to Implement that
in this code of course will not be
working with humans anymore let me just
remove the entire code from here
and all gone and let me also make sure
that this is empty gone so we have a
very simple method which is main here
now what I want to do is I want to take
the same example of calculator here so
let me get a class called calc and of
course I can just create this thing uh
in some other files as well that
actually makes sense but just to keep it
simple I'm using the same file here
so we got a class called calculator and
in this I can add some methods and some
variables so let's say I will Define
some methods here and I will say public
and it can add two numbers it will
accept two integers as well I will say
N1 comma and two so we got two variables
right and then I can just return N1 plus
N2 okay now let's say in this calculator
we have two methods one is ADD and one
is sub which is sub here and there's
there will be a subtraction operation so
we got two methods right now one thing
to remember if you look at file explorer
every time you get a file it also
creates a class file so for every class
in your code it will have a class files
we have used a calculator a computer
human student before and that's why we
have all these classes what I will do is
I will just delete them okay so you can
see all these classes are gone in fact
let me also delete the demo one to see
what happens and that's fine you can
also delete you can delete all the class
files so every time you compile the code
it will also create a class files for
you let me let me show you that so I
will say Java C and if I mention the the
file name which is
demo.java the moment I say enter it will
create two class files because we have
two classes if I go to explore you can
see we got demo.class and we also have
calc.class now when you run this code if
you say Java and if you say demo uh it
will just run the class files and as you
can see we are we don't have any code
here for calculator so it will only run
the demo class
and that's how it works so if I just try
to write this code here which which we
already have and if I try to create
object of it let's try creating object
of it in fact it let me know one more
thing before we start
let me for this example let me cut this
part and create a new file and let me
say this is calc dot Java uh and yes we
have this code here so you can see now
we have two files and before I continue
I will just delete this class files
again
okay class file deleted and now let me
just compile this code once again
so if you can see when I'm compiling it
it is only compiling the demo file it is
not combine the class dot Java right but
when I create an object of it if I
create object of calc obj equal to new
calc of course if you want to use it we
have to create object first and now if I
recompile this and let's look at the
class files we got the class file for
class as well so if you are not using
calc it will not compile it it will just
say hey my responsibility is to compile
the Java file I'm doing it but if you
want to work with the class the
calc.class as well or crack.java as well
you have to create object and that's how
it compiles now once the compilation
done you can Simply Save the value in R1
or we can say obj dot add it will add
two numbers let's say four and five and
then we can also find R2 which will be
result of subtraction so I can say sub I
will say 7 and 3. okay so basically you
can see we got these two methods and
when you try to print the values I will
print R1 and I will give a space and
also print R2 so basically I'm just
printing two values back to back and if
I say come file again because we have
made some changes and run you can say we
got 994 so four plus five is nine seven
minus three is four and that's what we
are getting here
everything is working fine right now
there are two conditions here why we are
going for inheritance the first one is
what if you want to add some extra
features you want so let's say if
someone is asking you for hey you know
uh Naveen I want a calculator and I want
two features addition and subtraction
what will be the cost I would say okay I
will charge you ten dollars now let's
say if the same person come back and say
Hey you know I want a calculator which
has four features addition subtraction
division multiplication and maybe at
this at this point I want to charge
fifteen dollars now of course I can add
those two methods here or I can create a
new plus you know why is because if I
edit the same file if I add more
features here I can't sell calculator
for ten dollars now I have to make a new
product worth fifteen dollars I don't
have calculator I have advanced
calculator which does four operations I
want both the models I want to sell the
10 calculator and a 15 calculator that's
one reason okay so let me just do that
so let me create a new calculator and I
will say this is advanced calculator
which has all the features dot Java and
in this I will basically have two more
methods which is public and multi which
will take two values and it should
return N1 into N2 and likewise we'll
have one more method here for division
so this is div
and division we have to say slash that's
it so we got advanced calculator which
has two features but now if I create an
object of advanced calculator now
instead of normal calculator I can I can
access multiplication and division I
can't access add and sub and that's why
you can see we got another here it says
the method add is undefined for type
advanced calculator that means in this
we don't have add-in Supply so what do
you think what could be solution here
think about this so one solution which I
can see is just write those two methods
here of course we can do that okay we
can just copy copy and we can paste it
here but don't you think we are writing
the same code again and again now when
you repeat the same code it is called
redundancy right we have same code
multiple times and redundancy is a crime
so make sure that you don't repeat the
values you don't repeat the methods
definitions and classes the point is if
I don't Define it here how would I
access them that's where the inheritance
concept comes into picture so United
says hey don't worry if you already have
a class called calc you can simply say
extends calc your job is done okay so
you simply say advanced calculator
extends calculator and now all the
features of calculator comes in here and
there's one more Beauty even if you
don't have this Java file that's fine
for inheritance you need a class file
not a Java file so even if you delete
this it will still work okay so that's
the first first reason even if you don't
have a code ready with you if you do
even if you don't have a Java file you
can still use a class file okay so
that's the beauty of inheritance we are
simply saying extends calculator which
is this class now what do you think will
it work let's try
so you can see there's no problem add-in
subtraction working we can add some more
variables here I can just copy this code
and paste paste another same line
this is my R3 this is my R4 and I can
just say this is multiplication okay so
multiplying number like uh let's say is
5 and 3 okay and then dividing the
number let's say 15 by
four let's do this and now when I
perform this operation of course I want
to print R3 and R4 as well on the same
line I'm lazy to write multiple lines of
code here and R4 so we are printing
everything in in the same line let's try
what happens compile no problem
run how it works you can see that
addition is nine uh suppression is four
multiplication is 15 if I'm not wrong
yeah and division is is three so 15
divided by 4 will give you a quotient of
three
okay cool this is working right so this
is how we use inheritance so important
thing here is this advanced calculator
here is called a subclass this
calculator here is called a superclass
and to inherit we use a keyword called
extends okay and this is basically a
relationship of is a uh advanced
calculator is a calculator and that's
why we say is important about that cool
can I can I have multiple classes in
hitting each other we can that will say
in the upcoming videos at this point we
just went for a simple inheritance where
we just use the feature of our
superclass you can say parent has all
these two features child is just
extending it or using it I can say this
is nepotism so so basically we were able
to do two advanced calculator which uses
a feature of calculator right so this is
extends now what if in future let's say
we got one more requirement we want to
build a let's say scientific calculator
and I don't know the operations I will
just say advanced calculator I'm very
bad with names I will just use this and
this advanced calculator will have extra
feature let's say it also has a feature
of finding the power of a number okay so
let's say public int I can simply say
power
I want to do that so it will take two
numbers the first value N1 and I also
want a power let's say N2 and let's say
this will return okay how do we do the
power so basically we have a math class
I can just simply use it matte dot yeah
we have a function of power just take
double value but that's fine I will just
pass integer double also takes integer
value N1 into
and the problem is it also Returns the
double value if you can see Power
returns a double value so what I will do
is let me return double value okay so
you have a choice you can return double
value or you can just Typecast it with
int and you can do that otherwise double
is okay so you can see we have a power
function which takes this method and it
it calculates now the thing is if I want
to create object of power when I will do
that I will just create that in demo I
will say hey if someone wants to try
very advanced calculator they can do
that okay it's just that very advanced
calculator if you can see we don't have
any other methods okay now that's
that's an issue right now I know in your
mind you have a solution right you have
a choice you can just add you can just
type all these methods here or we can
come back here and say extends okay now
it will extends what if we can also say
calculator but then this will only have
addition suppression division
multiplication but not the feature of
advanced calculator which is oh it will
not have this two as well because this
two is there in advanced calculator it
will only have ADD and sub you can see
multi and division not found
in fact you know I should also have R3
in fact this should be of type double
double R5 equal to obj Dot Power by
passing two values one is let's say four
raised to two at least we know the
output it should be 16 uh and I also
want to print R5 oh we are printing
everything in one line great and you can
see multi individual does not not
working so if you want to make it work
you can't just extend calculator you
have to extends advanced calculator so
you can see we have multiple hierarchy
here so very advanced calculator is
extending advanced calculator advanced
calculator is extending calculator so if
you try to compile this code let's see
if this works compile and run
you can see it's working you you got 16
at the end you got points over because
we are returning a double value this
works so if you're trying to imagine
this what we are doing is so we have a
calculator and then advanced calculator
is extending calculator and then we got
very advanced calculator is extending
from advanced calculator now this is
when you are saying multiple where we
are doing inheritance right so this is
called
multi-level enhance so basically we have
multi-level inheritance here because we
have multiple level but in the earlier
example we were having a just two right
so we were having this two now when you
say only two classes this is called
single
level
s and I know because I became a doctor
there but you got the point right so if
you have multiple layers that is
multi-level patterns and then you say
single that is single when you have only
two classes
now the very advanced calculator here is
taking the feature from advanced
calculator advanced calculator is taking
the feature from calculator so by
default all the character stuff will
come to varied once and that is
multi-level so in the last video we have
talked about what is single level
inheritance and then we have talked
about multi-level right now it is
multi-level so when you have the class
which is getting headed by someone else
and then someone else something else is
getting inhated by something else it is
multi-level now can we have a different
structure here let's take one more
example so if you say we have a we have
B and we have C now this is multi-level
right and of course when you have a and
b that's it this is single level but
what if you have a and b and then you
have C where your a is your parent in
fact in this situation as well if you
try to expand this one here as well we
have
this a as a parent
and then this B becomes a child
now b b becomes a child for a but then B
is also a parent
for C right so C becomes child here now
in the same way if we talk about this a
b c here we are saying both are parents
so we have a as parent and B as parent
and then C becomes a child
so C is anything from A and B both now
is it possible in Java let's try in fact
it is possible in other languages like C
plus plus let's try in Java what I will
do is I will just go back to the same
class okay same file demo and here let
me get a class called a and of course a
will have some methods this should be
capital A and then Class B and Class C
okay we have this uh three uh classes
here okay and let's say C is okay let's
try this first if B extends
from A and C extends from B okay this
works we can say there is no problem
here but what if I want the seed to
extend from A and B both as you can see
this syntax is not working it gives you
an error as well you can't put a comma
when you say extends a comma B okay does
it means we can use extends
extends B now even this will not work so
it doesn't matter what combination you
do multiple inheritance in Java will not
work
yeah so this thing will not work
multiple enhancements will not work but
the question is why so let's try to
understand that here now let's say if we
go back to this particular example here
let's say
you create object of B okay in this
scenario if you create object of B let's
say obj
now obj can call all the methods of b
and a both so let's say in B we have a
method called show okay let's let's say
there is a show method and then
from obj you are trying to call show
will this work yes this will work let's
say in a we have a method called ABC now
if you try to call obj Dot ABC yes this
will work but what happens you know when
you say obj dot ABC it will try to
search for it first in the b class in b
class we don't have it so it will say
okay I don't have that method maybe my
parent class will have so it will go to
a by checking hey do you have ABC parent
will say yes I have now in this case it
will work
the same thing is applicable for c as
well let's say if you create object of C
which is obj again and then if you try
to call a method let's say let's say a
has a method called X B has a method
called Y and C has a method called Z so
let's say we have Z method and then when
you're trying to call Z this will work
because in C itself we have the method
if you say obj dot y will this work yes
because it is coming from B now when you
say obj dot X it will also work because
it will call from a so first it will
search in C in C we don't have X it will
go to B in B also we don't have X it
will go to a yes in a we have X okay it
works but now if you come back to this
example let's say if you get object of C
as object so let's say this is C object
okay and then if you let's say in this a
we have a method called show okay and
that's how that's how we're working so
let's say if you if you call show now
now of course c will say okay I don't
have a method so will this work let me
ask my parent so it will go to a a will
say okay I have show problem solved this
will work right engine I'm not talking
about Java let's say in general this is
how it works now let's say we have in B
we have a method called X okay now it
will say obj dot X will this work now it
will search and see and see we don't
have it in a also we don't have it in B
we have it so this will also work
okay but what if there's a method called
Y which is there in a and b both okay
and now if you are trying to say obj dot
y
the problem is from say we don't have it
and a and b both has this method which
one you will choose that's a confusion
right
uh it is almost same like let's say if
you want to call someone your phone is
dead and then now you want to call so
you can ask your patents and both the
parents has a phone which one which
phone you will choose now if you chose
your dad's phone
your mom will feel bad if you if you
choose your mom's phone your dad will
feel bad again I'm just giving an
example here I'm not saying it literally
happens but in fact they will be happy
that you're not using their phone but uh
yeah that's a confusion we have here
right now this problem is called Ambi
Beauty problem okay so ambiguity simply
means we have we have a confusion here
which one to choose
now this problem is there in multiple
languages which supports multiple
enlightens Java says oh that's a problem
let's remove the feature itself
okay I know that's a weird way of
solving the problem but yeah they have
removed the problem itself so it's not
like they found a solution they said
instead of finding a solution let's
remove the feature that's right in Java
multiple inheritance does not work okay
so in the it's a very famous interview
question uh do we support multiple
entities in Java and the answer is no
there is a indirect way not actually a
way it's just that it is possible by
going all through steps but yeah that's
how Java is implemented in new feed in
new versions they have done something
which changes it uh with the help of
interfaces but we don't know interfaces
yet so let's talk let's say Java does
not support multiple enhancements
oh okay this makes sense so once we
talked about inheritance and Method
overloading as well right we have talked
about method overloading in this video
let's talk about method overriding
that's right so we have two different
method overloading and Method overriding
so let's talk about overriding here so
for that what I will do is I will just
try to keep it simple again and let's
use the class A and inside this class A
let's say we have a method so I will
just remove this part and here I'll say
public
void show just to keep it simple I'm
using a very simple example here which
is uh show which prints something let's
say it prints in show okay now if you
have a method inside a class of course
you can create the object and you can
call the method right and we have seen
that so let's say if I go back to my
main method if I say a obj equal to new
a and I can simply say obj dot show and
it will work right and it should work
that's what we have done from a long
time so let's compile this code and run
and you can see it prints in show just
to keep it simple we have we have went
with a very simple example now what I
want to do is I want to get a class
which is Class B and I want this class b
to extend Class A and of course when you
talk about inheritance this method show
it also will be available inside Class B
right so if I create object of Class B
yes of a it will also work because
that's how many items works right so if
I go back compile and run it works you
can see we got in show what I will do
now is I will also print in a show just
to differentiate that this is getting
printed in the a class okay now the
thing is
what if you want to have a different
definition of it okay why do we need
different definition let's say we got
two methods here public wide config so
let's say we have this method which is
called config I don't know what it will
do just to keep it simple I will just
say s out and I will say this is in a
config okay and let's say they have
different implementation they have
different statements at this point we
are not focusing on statements we are
here to understand the concept right so
let's say it does something show method
and config does something and I can
actually call both the methods not just
one I can call config as well okay and
if I
compile and run this code it works you
can see it says in a show in a config
now let's say I want a different
definition for sure okay not for config
so basically what I want is when when it
comes to B and when I call show it
should print in B show
how do I do that how do I change the
execution so what I want is when I call
show it should not call the show of a
because show of a will print in a show I
want to use config as it is so I can't
even remove this inheritance if I remove
this and if I Define the methods of
course I can Define show but then I want
this config to be coming from a so of
course you have to keep it you have to
say Class B extends a because we want
config what we don't want of a is show
because it is printing in a show I want
to do something else
and that's an audio you can say public
void show you can write the same method
name or maybe a different name you can
say in show one I mean so one and you
can print here in B show I mean of
course you can do this the only thing is
if you come if you execute this code now
it will still print in a show you know
why is because we are calling show and
both these methods are different one
with name show and one with name show
one
okay that means if I call show one then
it will work then it will print in B
show but what I want is I want them to
have a same name I want my this method
which is so
should override the method here
is it possible and the answer is yes in
Java we get this amazing feature where
you can basically override the methods
of the passing class so of course you
want everything except this part
okay I mean except this show method I
want config but I don't want show now
let me give you one more example here
remember when we talked about
inheritance I have used an example where
I was not having any phone in my 10
standard and my father had a phone which
is double three one zero now if you ask
me at that point which phone I have I
used to say double three one zero
because that's my father's phone
but after two years when I was in my
12th standard I got my own phone I got
Motorola c168 again uh not a smartphone
but it was good it was a very slim phone
so when now if you ask me which one I
have I was I will say I have Motorola
c168 my father still had double three
one zero so here if you can see
if someone asked my father father will
say I have double three one zero if you
ask me I have a choice of saying double
three one zero but I will go for c168
which is my phone right so you always
give preference to your own features
first example if you call show here it
will execute the method of b instead of
executing the method of a so basically
this method show
overrides the method of a here and we
can simply execute compile and Quran you
can see it prints in Bishop now this
will make much more sense when we say we
are creating not a but we are getting a
calculator
which has a method called let's say let
me remove config for some time let's say
that we have a method called uh add and
this will return a value okay and here
instead of printing this I can simply
accept two values I can say int and one
comma int and two
and here we have done this before and
that's why I'm writing this code very
fast against a return N1 plus N2 okay
so if your class which is instead of
saying B I can say Advance calc which is
extending calc it will also have some
features but let's say I want to add two
numbers which will also take int and it
will have the same parameter okay
because in method overloading we have
seen it can have the same method name
but different parameters here in method
overriding it will be same name same
parameters as well I mean same type of
parameters not the name doesn't matter
name uh let's say N1 N2 and it will have
the same name same number of parameters
same type of parameters but it will have
a different behavior let's say N1 plus n
two plus one I'm just adding extra 1
there so what I want is if I come in
this section okay at this point I'm not
overriding it I just have ADD method
inside calc and if I create the object
of advanced calculator by saying
advanced calculator obj equal to Nu
advanced calculator
and if I try to call the add method by
passing three and four of course 3 and 4
is 7 so if I get this value somewhere if
I say int R1 is equal to and if I print
the value for R1 and again since we have
done this code before I'm just typing it
fast
now what do you think what will be the
output I am passing 3 and 4. so of
course it will first search for this
method add inside the same class of
course we don't have that method so it
will go to the upper class by saying uh
hey you know uh calc you are my
parenting class I'm searching for ad
with you and yes it is available
so basically we can just compile this
code and run you can see we got seven
and that actually works but now I want a
different definition for add I just want
some changes instead of adding those two
numbers it should also add one at the
end okay so if I compile this code now
and run it will print eight so this ad
is overriding the add method of
calculator okay just remove this
statement that's extra so this concept
is called method over writing so this
method is overriding the method here I
hope that makes sense right in this
video let's talk about packages the
thing is whenever you have a file
doesn't matter is it a music files or
documents or code we normally put them
in a folder right and then we create a
folder structure as well in fact I
remember in my college days when we used
to store different songs you know we
used to create different folders like
you know we have a songs folder then
inside that we have rock songs DJ songs
songs romantic songs and in fact in that
as well when you go to sad songs we can
have normal sad songs ultimate sad songs
okay now that's exaggeration but we do
that right we create a structure there
in the same way when you talk about Java
project you will not be creating one or
two files right it would be having
multiple files sometimes your project
can have let's say uh 200 files 300
files okay maybe most of the time when
you have a complex project now how will
you put all these files in one folder
you can actually you can put everything
in one folder now if you see our project
structure here what we did is we have
this folder called codes and in this
codes we have all the files in fact we
only have three files now but just
imagine we have more files imagine we
have 100 files it's okay to put them in
one folder but it's always better if you
can create a structure where you can
have few files in one folder and few
files another folder and then you can
have a folder inside a folder now
normally this type of pattern in in Java
is called packages normally you you
store files in a package so yeah that's
right the folder is package here and of
course one package can be a part of
another package the way you have folders
inside a folder so how do we do that
here in Java so make you understand
let's say we have these two files you
know advanced calculator and calculator
now these two files are related right
they both work for the calculator so it
is a good idea to put them in one folder
now how will you do that you know you
have an option here of creating a new
folder that's one way all you can what
you can do is you can just come back on
top of your class and say you can create
a package so the keyword which you use
to create a package is called package
and you can put this class in that
particular package let's say the package
name is tools right so of course you can
create any pack any package name but it
should have one it should make some
sense so you can see I'm saying that
they are tools
okay and the thing is you can see we are
getting an error it says that declared
package tools does not match the
expected package the thing is you don't
have calc inside the package in fact
most of the IDS will give you an option
of directly if I click on Quick Fix yeah
so you can see most of the IDS doesn't
matter which ID you are using in vs code
we have this option in most of the
famous ID you will get this option of
doing something some red red symbol or
something like that here we have an
option of quick fix if I click on that
it says move calc.java to package tools
okay that is a good idea we can click on
this and you can see it created a folder
called tools
and now we can actually move this to
tools as well the only thing is when you
do that and when you go to this
particular class
okay it has already done the changes you
can see I have not written this it is
already there thanks to vs code and the
IDE uh so basically you get this here so
it's always a good idea to put your
classes in a package you can create a
complex structure if you want you can
create a one more folder here let's say
we're going to folder called database or
maybe DB connections or DB classes or
maybe you can say simply said DB now
this DB will have all the database
connections so let's say if you want to
create some files which will connect
with mySQL Oracle or it does something
with database so you can put all those
classes in database folder okay now
that's how you create a project
structure here
okay the only thing is if you want if
you have this structure here let's say
if you have calc and demo Advanced calc
and if you can see both are in a package
now the only problem you will face is if
you go to demo and you can see demo is
not a part of any package normally you
put the main class so the class which
has a main method separately outside the
package so that you can easily access
other classes
okay when I say easily access another
classes can I do that can I create
object of calc here so if I say calc obj
equal to new calc which was working
earlier if you remember our previous
examples
it's not working now you can say it says
calc cannot be resolved what's wrong the
problem is demo and calc now they are in
two different folders you can't directly
access it okay so when I say you cannot
directly access it do we have an
indirect way uh yes we have an entire
way so what you can do is if you if you
see this bubble
it says import calc that's right if you
want to use calc in your particular
class you have to say import calc but
then calc belong well calc belongs to
tools.calc so basically you have to
mention the package name and then you
have to mention the class name whichever
you want to import and now you can see
there's no issue how about advanced
calculator if I want to use advanced
calculator obj1 is equal to new advanced
calculator okay now you cannot access
access this one you know why is because
we have only imported calc not advanced
calculator how will you import this you
are right just come back here and say
import tools dot advanced calculator so
whichever class you want to use you can
just import them in fact Java internally
has a lot of classes example let's say
one of the classes which we are going to
see in future which is let's say list
now when we use least which design build
class or with input interface what is
interface we'll talk about that later or
maybe at this point we can talk about
let's say add a list which is a class
when we use analyst and when you create
object of it I will say list is equal to
new
add a list now the moment you do that it
will also come from a package you can
see it is now given given by the IDE it
is auto completing it but if I remove
this line you can say it will give you
error it says allergies cannot be found
so we have to import this one as well
and this belongs to a package now that
package is import
java.util dot as a list this is up to
you have to import now you might be
thinking why we have two dots here Java
dot util how it looks like so basically
we have a Java folder inside Java folder
we have a util folder so it's the folder
inside the folder and Java has multiple
folders efficiency Java dot we have
applet folder we have awt folder beans
folder Lang folder IO folder and all
this thing so in general whatever class
you use in Java belongs to a package let
me repeat whichever class in build class
which you use in Java belongs to our
package now you will be saying okay
everything makes sense but don't you
think string is also a class and one of
our favorite
class which is system system is also a
class right so when we are using system
we are we have never imported it so when
I say system.printer then there was no
need to import the package but the
system belongs to our package and the
answer is yes if I go to system and if I
go on top here can you see that it says
package so this class system class
belongs to our package java.lang but we
never imported it the thing is by
default every Java file will have
java.lang by default imported so even if
you don't mention that it's there this
line is there even if you don't mention
the thing is it's actually this not this
line what is by default is this
java.lang.star now what is this star now
in one particular folder if you have
multiple files and if you if you want
all the files you can simply say start
just like we have tools here in tools we
only have two files and we are importing
both so can we just do that yes we can
so we can simply put a start here our
job is done and by doing that I've also
removed the list we don't even need that
you know that so basically if you want
to import all the files you can say
start okay so that's how you can create
a package in Java as I mentioned you can
create a folder inside a folder example
let's say if I have a folder called
other so let's say we have other folder
and these tools actually belongs to
others so now if I move this
you can see we have tools inside the
other now how it will look like when you
talk about your the calc so you can see
it says other dot cap so you have to if
you want to go inside the package
normally in folder structure we use
slash here we use dot so just others dot
tools dot uh calc okay that's how you
have to import it and of course you can
say start it will import everything
now my question to you is if I say
import other dot star now is this two
line same
or can I remove this of course right
when you say start it should input
everything but now if you can see it is
giving you error the reason is
when you say others.start it so star
simply means all the files not all the
folders okay so in other if you have
some files let's say if I create a new
file here I will link this as a DOT Java
the moment you do that you can see this
a class belongs to other package now you
can easily use a but not calc so if you
say a obj 2 is equal to new a this will
work is because you are saying others
dot start it will import all the classes
which are all the files in in the other
folder not inside a folder which is
tools so if you want others I mean tools
as well so you have to mention
others.tools dot star so that's how
basically you use a package structure
now there is one thing you know not
important at this point but since we're
talking about package let's talk about
it because you will be seeing those type
of structure multiple times when you
create a project a big project normally
you deploy your project on the server
somewhere right
and maybe you're creating a library
that's right what you do is when you
create a project it's not always for
your use sometimes you create libraries
so that others can use your files now in
this case as well you will create a
package and then you will give your
package to others
the only thing is when you are sharing
your package to the entire world it
should be unique it should have a unique
name let me show you something I will go
to a website now this is one of the
website where you can get the libraries
the library simply means if you want to
do something and if you don't want to
write your the code entirely by yourself
you can use some libraries and most of
most of the time we do that example
let's say if I want to connect my
application with mongodb which is a
database so I can simply search for
mongodb drivers sync this is a driver
which we use to connect Java with
mongodb so you can use this package in
your project okay let me select a
version
so this is the package
okay now the thing is when you talk
about this package what should we name
of it so this name should be unique on
the internet now how will you make
something unique that's tricky point
right so when you are creating a project
how will you make it unique so one way
to do that is by reversing your domain
name that's right of course right when
you're building a library you will also
have your website your company website
maybe so let's say if you talk about a
company like Google so if I'm working
for Google and if I'm creating a library
so what I will do is I will name I will
say this belongs to a package so if I'm
making a project for let's say Google
and I'm making a calculator or advanced
calculator so I will say com dot Google
dot uh calculation now this is my
package name okay so by making
com.google I'm making sure it is unique
right only Google can own this domain
right it's their domain so that's how
you do that so depending upon your
project you will see this type of
packages in fact in future videos we
will be using some packages which have
com dot something it means they have
just reversed their domain name just to
make it unique but again for learning
purpose you can name your package
anything you want example the way we are
doing here pack each other but it should
have it should have a meaning that's
important now once we talked about
packages it's a good time to talk about
access modifiers now one of the access
modifier we have seen in fact we have
seen two private and public
apart from this we have more we have
protected and default as well so in this
video let's try to explore them or one
or two videos so what I will do is
initially I will start with public now
what is public basically let's go to
demo and we have we were trying to
import the packages and of course we
should do that right anyway we don't
have to do that java.lang it is it comes
already so we don't have to worry about
it and now what I will do is I will just
go back to my class A let's work with
class A now and in this class A you can
see that class A is public okay and it
belongs to a different package called
other and in this class I will just
create a variable called int let's say
marks so we have this variable called
marks and the let's say initial value
for Marks is six because we just want to
access this is it working or not now how
will you access this variable so you can
just go back to demo so we have ADD we
have a right which has this code which
is simple class and then we have our
marks let me go back to demo and in this
I want to access it so I will just
remove all this lines just want to work
in fact tools is also not I need now
that only work with other and in this
let me create a object of a now
connected object of a yes we can because
we can access it and then I'm just
trying to say obj dot marks now I'm not
trying to do that you can see it gives
you an error it says the field a DOT
marks is not visible
I mean that's weird it's there right
Marx is there the thing is it is not
public now when it is not public you
cannot access it outside the package you
can see that that's the issue we got now
what if you have a class in the same
file or maybe in the same package let's
say in the same package which of which
is of demo I will create a file called B
dot Java and in B dot Java let me just
say because they're in the same package
now so no package is same package
basically I will try to create a
variable called int let's say marks
let's see if I can access this marks and
demo I will just go back here and I will
repeat the same sentence same line in
fact two same same statement with the
help of B object now this is B the only
thing is we have to use a different
object name because we cannot have same
and using this obj can access marks so
you say there is no issue even if marks
is not public it's no issue because they
are in the same package the moment you
have a different package and if you
don't mention public it will not work
okay that's the issue you can see it is
not working now if you want something to
be accessed outside the package always
make it public and that's why methods
most of the time they are public
variables should not be public but
method should be public example if I say
public void show here now show can show
is acceptable I can use show from
anywhere example if I can come back here
obj dot show this will work because
that's public but if I don't write
public that it will not work but that's
one so public means it can be accessed
from anywhere okay now apart from public
we also have a private so if I talk
about private can I use private anywhere
private variable can be used in the same
class irrespective of the package okay
package the secondary part it can be
used in the same pack same same class I
can't even use outside the class example
let's say if you look at this B and if
you look at this demo they're in the
same package right
but now if I create a private variable
there here if I make this as a private
variable which is which you should
always Mark your variables as private
the moment you make it private even if
the same package you can't access it so
private variables can be used in the
same class irrespective of the package
it's on the same class now let me do
iterate when you talk about public it
can be used from anywhere okay you can
see this table a public can be used from
anywhere
private can be used from the same class
okay now apart from public and private
we have two more okay let's talk about
those now now if we talk about this a if
you don't mention private something
should be applicable right if it is not
private is not public what is it so by
default there is something called a
default access modifier okay which is
also called private protected but we'll
talk about that later but it is called
default Now default simply means it can
be accessed in the same package it's as
simple as that it can be accessed in the
same package example if we talk about
this B when private was not there it was
able to be accessed in the same package
so we got private which can be accessed
in the same class we got public which
can be accessed from anywhere and then
we got private which can you only be
accessed in the same class and default
in the same package okay apart from this
we have one more which is called
protected now what is protected now
let's say we have this class A which has
let's say if I make this variable as
protected okay and then I'm going back
to demo and inside this demo somewhere
I'm creating a class in the same package
basically it doesn't have to be in the
same class or same file in a different
package basically let me create class
called C and then I'm saying that this
class extends
a now in this class A so you can see
this is protected uh can I use protected
in some other package
you can see marks is predicted in the
other package like demo again Marx is
not working so basically
if you make it protected you can't use
it outside the package before coming
there you try to know what we should do
let's try to create a class here itself
let's say a class called launch and in
this class let me have a method which is
public void ABC let's say and let me try
to create object of a equal to new a
and see from here can I try if I try to
use marks let me just print marks obj
dot marks okay it is working so it works
in the same package
but it doesn't work in other packages
okay so you can see demo is another
package but what about a subclass we
have class C here and then
if I try to create
a method public void ABC and you can see
this class C looks same in both the
packages the difference is this is a
different package and it is extending a
now and now if I try to access
marks it works there's no issue you
cannot access marks outside the package
but you can access marks outside the
package but it should be a subclass
if you can see C is a plus of a now if
you see this image here this image looks
like right
let's talk about private private can be
used in the same class nowhere else
protected can be used in the same class
in the same package
in the other package but subclass
public can be used everywhere
default can be used in the same package
okay it's it's that simple so this is
how you specify the modifiers now how do
we use and which one to use basically
the idea is very simple
try to make your classes public which
you are doing and of course we don't
have a public here the thing is you
can't even make this class public
because you cannot have two public
classes in the same same file
but and the general idea is in one file
you should have only one class
so try to make your class public next
try to keep your variables the instance
variables private the methods most of
the time will be public but if you think
there is a method or a variable which
should be accessed only in the subclass
of other packages use predicted try to
avoid default default is not something
we should be using I know from from if
you check all this thing we are
promoting default a lot but don't do
that don't use default stuff example
this is default either make it private
public protected or public don't keep it
default default simply means you don't
know what to give the access so give it
private predicted or the public in this
video let's talk about polymorphism
remember we have talked about method
overriding and then we say there is
something more this is where we are
talking about so we have a concept of
polymorphism now this is a very
important Concept in terms of op and
most of the languages which implements
Ops has this concept now what is
polymorphism now basically as a concept
it has two words one is Paulie's second
is morphism now Paulie simply means many
and morphism means Behavior now what it
means is there is something which
behaves differently in different
situation based on uh yeah based on
situation let's say as a human you
behave differently at different
locations right example for as at home I
behave differently at my office I behave
differently when I'm with my friends I
behave differently right so that
situation changes me in the same way
because the name also changes right at
home I am uh I'm a son husband of a
father at office I'm a colleague I'm a
boss I'm an employee at my with my
friends okay they use different words
but then let's not mention that so the
important thing is your behavior your
name changes at every place right your
behavior changes based on that in the
same way in the world of object oriented
we have a concept of many Behavior
polymorphism so the same object or the
same reference will have different
Behavior based on how you create these
questions of it now to implement this
there are multiple ways in different
languages but before we go into the
implementation let's talk about its type
so there are two types of polymorphism
one is called a compile time
polymorphism and second is called a
runtime polymorphism of course they have
different names uh some compile time is
also called early binding runtime
problem is also called late binding but
we have these two words compile them at
one time now what do you mean by compile
time see if you can Define your behavior
so the behavior is defined at compile
time that is compile to polymorphism if
the behavior will be defined at runtime
that is called a runtime polymorphism so
when you compile the file and when you
know what thing will be executed at the
compile time itself it is compile time
now which method will be executed will
be decided at runtime that's run time
now we have done two examples here which
is overloading and over writing so if we
talk about overloading it's a part of
compile time because at the compile time
itself example let's say if you have two
methods you have let's say two methods
which is ADD which takes two parameters
ain't
an INT
and then we have one more method here
which is ADD and when you say ain't
ain't in which takes three parameters
now both this have the same name but
different different parameters that is
Method overloading now which method to
execute will it will you execute the
first or second method will be decided
at compile time now let's say you have
two classes Class A and Class B two out
of two different classes and Class B
extends Class A we have talked about
this in method overriding and let's say
you have a method which is ADD which
takes two parameters and also here we
also have the add method which takes two
parameters
now out of this too which one will will
get get executed it will be cited at
runtime so this that is called a runtime
polymorphism in fact there is one more
concept which we are going to discuss in
the implementation when we talk about
Dynamic method dispatch at that point
this thing will get more clear but just
to generalize what is polymorphism
polymorphism means many Behavior so your
behavior of your reference or your
execution will change based on some
situation if it is compile time which is
your method overloading where you decide
based on the parameters at compile time
itself in runtime you're not sure which
method will be called because both the
methods have the same name same
parameters now in this video let's talk
about Dynamic method dispatch now once
we have went through what is
polymorphism we have also mentioned that
it is same thing multiple behavior and
we have two types of uh polymorphism
which is compile time polymorphism
runtime polymorphism now to implement
runtime polymorphism let's try one more
example here and we do that with the
help of dynamic method dispatch again to
keep it simple we'll use a simple class
like Class A and then we got class B and
let's say Class B extends Class A okay
and let's say we have class C
and again we have discussed most of the
topic so let's make it quick so we got
class C so if you can see we have class
A which is getting extended by B and C
both so you can say class A is parent
and we have two Childers one is B and
one is C now what I will do is in this a
I will create public void show okay and
this show will print let's say in a show
okay and we'll be using class a bit
later as of now let's only focus on
Class A and Class B now my question to
everyone is I mean okay let's remove
this classy just to remove the confusion
let's go step by step so let's say we
have these two classes Class B X is
Class A now my question to you is how do
I create an object of Class B and of
course we have talked about this from a
long time I can say b obj equal to new B
and that's how you get the object right
and of course using this obj I can call
show there is no harm compile this code
and run you can see we got in a show now
this is how you create the object right
now there is one more thing
can I create a reference of a an object
of B is it possible since B in B extends
a so you can say B is a child of a so
can I refer this obj as a and the object
of object is B now when you look at this
obj what is this obj it's a variable
right and what is a type of a variable
the type is a here right so the obj type
is a but the implementation is B okay
that's the point remember and this
perfectly works now if you want to
imagine this let's let's go with this
one more example here which I will write
here let's say if I create a class
called computer and of course class
computer has some methods okay and then
class laptop and we all know that laptop
is a computer so I can also say laptop
extends computer yeah we can say that
right and now
if I say laptop is a computer if I want
to create object of a laptop of course I
will do it it's very simple you will say
laptop let's say lap is equal to new
laptop so let's instead of saying uh lab
we say obj1 and then I can just call all
the methods but my question is can I
refer this obj1 as laptop yes it is a
type of laptop I know I can also say
this is a computer and that's what you
do right when you look at the laptop you
can say hey that is a laptop but that's
also a computer we are referring that as
a computer so we are referring this obj
which is an object as a computer but
technically it's a laptop right in the
same way we can refer this obj of type A
so we can mention the type as parent but
the object can be of child okay so I've
just created this laptop computer just
to show you let me remove that
so yes it is possible to create a
reference of a superclass and the object
of a subclass okay and this will surely
work let's compile there is no issue
let's run and you can say it says
initial
but the twist is
if I have the same method and we have
talked about this in method over writing
if I have the same method and if I say
this is in B show
now what it will call Will it call in
Asia or in B show as per the method
overwriting it should call in B show but
look at reference reference is of type A
that's tricky right uh let's try in fact
what I will do now is just to first
let's run this code and I will show you
something you can see it says in B show
let me initially set the object of a
itself
and then let's go step by step so I will
say compile and run it says in a show in
fact I can call this obj show once more
but before calling object show what I
will do is I will make one change here
I can just come back here and you can
say obj is equal to new B that's right
we can assign a new object to the old
variable okay now if you want to
understand this with a memory of course
we have a stack here right in this tag
we have different variables and then we
have a heap memory here now initially
when you say obj that's your object
right and it will create object of a so
1 0 1 is object of a and talking about
line number 24. okay line number 24 we
have this line so that's an object here
and it will have some methods the method
name is show itself right and this will
have a value which is 1 0 1. so I'm
talking about line number 24 okay and 24
this is a link now when you say obj dot
show line by 25. so at that point it
will look okay so obj dot show that
means I have to call this show method of
object a so this my friend is an object
of a
and now on line number 28 we made some
changes that is now this particular
object is referring to the object of B
so we got one more object here which is
let's say 1 0 3 and this is an object of
B now okay this will also have a show
method because that is what we mentioned
there and now since we are changing the
value here this will be replaced by one
zero three there is no one zero one
anymore that means this link this link
is broken and we got a new link now on
line number 29 when you say obj dot show
it will call this show method of B so
it's not about what is a type of the
object or reference you can say type is
still a but the object is B and that's
what you call the B show let me compile
and run you can see at first for this
line it is printing in Asia for this 90s
printing in B show likewise if I create
another class here Class C which extends
a
and if I have the same method I will
just reuse my own code and if I said
this is inch C show what will happen if
I create if I just go back here and say
obj equal to new C and if I say obj dot
show what do you think what will happen
if I run the for the third time and
that's of course right different object
will have a different Behavior remember
runtime polymorphism and you can see we
got in C show so the same object which
is obj dot show is behaving differently
with different objects polymorphism
right so if you say we are not even sure
so when you compile this code at that
point we are not sure obj dot show will
call which method of of which class I
mean method of which class it will be
decided at runtime and that's what is
called runtime or polymorphism and all
this concept is called Dynamic method
dispatch because that's Dynamic which
method will it will call we are not sure
okay and that's how it works so Point
remember here is irrespective of what
type of object you have
or what type of variable you create is
it type it's a type A but it all depends
upon what object you have it is only
possible when you have inheritance okay
you can't simply say we are getting a
new class class D and you will say Okay
class D and you can't simply go back
here and say obj equal to New D this
will not work because D is not extending
a if you can see where if we can verify
D is not extending a so this will not
work this will only work when you have
inheritance so only you can have a child
objects for the parent variable which is
a obj parent type variable let's talk
about final keyword okay so the keyword
we are talking about now is final now
basically final keyword can be used with
a variable a final keyword can be used
with a method and a final keyword can be
used with a class and we'll go step by
step so let's start with the final with
variable
now when you make a variable let's say
if I create a variable called num and if
I say now the value for Num is 8. and of
course when you make a variable of
course you can change the valuator right
so initially the value was 8 and now you
are making it nine there's no problem
right and of course you can print the
value as well so if I compile this code
and execute the decent value is 9. now
there's a concept of making constants
right so what is constant so if you make
your variable constant you can't change
the value of it now the way you can do
that is by using a final keyword now in
different languages we use different
keywords I guess in C plus plus we use
const in Java we say final so the moment
you make your variable as final variable
the value the variable becomes constant
so once once you assign the value you
can't change it okay that's important
and that's why you can see we got an
error here in fact you can also get this
error by compiling the code you can see
it says cannot assign a value to a final
variable so that's final Yeah final
variable num okay so because num is
final you can't change the value and
this is actually very important so
whenever you have a value which will
which you think will not change try to
make it final it's a good practice to
make final variables is because you will
not get any unexpected output because if
you think the value should be constant
then y to even change it example if you
want to make a variable for pi we know
the value of pi right which which will
not change
so it's good to make that particular
variable as final so it's always a good
idea to make a final variable because
that's a stand that's what a good
practice is
so we have talked about what is final
variable so final variables simply means
making constants now let's talk about
final method in fact even before final
method let's talk about final class then
final method will make much more sense
so at this point I will just remove this
part so now we know what this final
variable is right so what I will do here
is I have a class here called let's say
calculator okay now I'm making this
class and in this or maybe let's keep it
simple let's say a so I've got this
class a right and now in this class I
have some methods let's say the method
name is public void show and you know
what let's make it calculated just to
make just to make it much more sense and
I will also say public void add this
time I will not return the value I will
just print the output here itself I will
say a
into B
and then I will just simply print a plus
b I'm just adding it here itself
right and then we got the method which
is show and here we are saying public
here we are saying in
calc show Okay so let's say we have this
class here which is calc and then we
have these two methods and if you want
to make it work of course you have to
get object of calc you will say calc
obj equal to new calc and with this
object you can basically call both the
methods you can say show you can say add
and you can pass two values 4 comma
let's say 5 right now with this let me
just compile this code and run compile
no problem and run you can say there's
no issue it is printing in calc show and
9.
now what if someone else is trying to
create a class called advanced
calculator
and maybe you maybe that they're trying
to extend they're trying to inherit the
features from your class which is calc
okay and by the way is possible anyone
can inherit your method or your classes
right because it's available
uh what I will do is I want to stop this
I want to say Hey you know no one should
be able to extend my class you want to
stop the inheritance how will you do
that so if I make this class as final
you can see it will give you an error it
says the type advanced calculator cannot
be a subclass of the final class that's
right so once you make your class Final
you are basically stopping the
inheritance okay so basically when we
talk about final variable it means you
cannot change the value of it when you
make a class Final it means no one can
extend it you're stopping the
inheritance okay that makes sense now
what if your your class is not final so
of course anyone can use it and maybe
you don't have an issue of people using
your class for your inheritance
the problem which we have is
someone will create object okay of not
your class but advanced calculator and
they will use your features and you are
okay with it because ultimately you're
printing your own class name which is in
character or maybe I can say bye Naveen
okay so maybe this this Calcutta is by
Naveen so if I compile this code and run
it will print my name at least I'm
getting the credit
but what if someone says hey you know I
will use your feature of Edition because
there is no great mention
but I will have my own create here so I
will create my own show method method
overwriting remember and I can simply
print by John I'm not sure who John is
but let's say if that person says bye
John now what will happen is when you
execute the show method and add
you can see add is my implementation but
they are just overriding show method and
it says bye John I don't want this I
don't want anyone to override my method
how do I do that
how do I stop over method overriding in
that case you can make your method as
final now when you make your method
final which we talked about here when
you make your method final no one can
override it you can see we got an error
cannot override the final method okay so
that's how we can use final keyword we
can use final keyword with variable to
make it constant you can use final
keyword with the class to stop in
heightens and you can you can use final
keyword with method to stop method
overriding so I hope I don't make sense
now in this video let's talk about
object class remember when we talked
about inheritance I also mentioned that
every class in Java extends the object
class so in this video let's try to
understand what is that so what I will
do here is first of all I will create a
simple class let's say class A so every
class in Java extends the object class
right so even if you don't mention it is
there but what is there inside this
class so what I will do is first of all
I will say let me create object of a
here I will say a
and uh okay so we got the object but
then using this object you can you can
see we can call so many methods we have
not defined any method in this class but
still we have the axis of equals method
then we got notify hash code uh notify
all two string weight
so many methods right now what they do
so let's understand that so what I will
do is in fact
this I will say laptop class just for
the example and here also let me get
object of laptop here so I will say
laptop obj equal to new laptop okay now
I will try to create some variables here
so I will say private int let's say
price and let me also get a string
variable here which is private string
brand okay so we got this two laptops
I can say model as well so we got model
and price right so if you talk about
MacBook or Dell XPS or Lenovo laptop so
it doesn't matter which laptop it is we
have a model and we have a price here
now if you talk about this particular
laptop here let me set the values to it
and timely you know what I will do I
will just remove this private so that I
can access it from outside here and I
can say oh uh okay so I will say obj dot
model I will set the model as let's say
Lenovo I don't know is it a laptop yoga
maybe and then I will say obj dot price
is equal to let's say thousand dollars
okay so I got a laptop I am I got the
values right what if I try to print the
object what happens behind this scene
when I try to print the object of course
we tried this before and it was giving
some weird output let's understand what
that output is now if you try to
concentrate on this output of course
this is not the values which we set but
it it prints laptop and it actually
makes sense because obj is a laptop
object and then we got the at the rate
symbol and then we got some weird
numbers I'm assuming they are heximal
values because you can see we got a d f
they are part of X decimal numbers okay
so these are the accessible format but
what is it let's try to understand that
now what if I say every time you try to
print end the object it by defaults
behind the scene it will call the two
string method let me repeat every time
you try to print the object it will call
to string method even if you don't
mention yeah and okay by doing those
changes let me just run this code once
again compile and run you can see this
it prints the same thing that means yes
it is getting called but what two string
is doing so if I go to two string now
first of all two string is not my method
if you can see in laptop plus we don't
have any method called tostring but in
the object class that is you can see we
got a two string method which returns a
string right that's what we are printing
right it returns something
what it returns it Returns the class
name if you can see it says get class
get class method will give you the class
name
then it calls get name so class name
okay that is laptop okay it's working
and then we got address symbol in
between okay that also makes sense why
we got it there and then it prints
something in hexa string that's why we
got hex decimal values here but what
exactly it represents it converts the
number into hex decimal string and that
number is actually hash code now what is
Hash code if you go to Hash code again
it belongs to the same class and behind
the scene implementation of a hash code
works with the it basically generates
the hash based on the values you have
okay now hash is a very simple Concept
in terms of cryptography and anywhere it
tries to create a single string of all
the data which you have so let's say if
you have a object which has five
variables it will apply a hash algorithm
and it will generate a string a number
string which will be of fixed size okay
to know more about how passcode you can
just go to YouTube and search for what
is Hash or go to Google and search for
what is Hash but at this point we are
returning a hash code okay that's what
we got here okay now the thing is we are
trying to print this right so body fight
is calling two string and that's why we
got this output but what if
when I try to print the object it will
print something which I want
and one thing we know that if you don't
have a method in your class it will call
the method of a superclass but what if I
create that method here itself so the
public method which returns a string the
method name is to string if I implement
this method and if I return something if
I return say hey that's it and if I
clear this and compile and run oh it
says hey you know it's not printing the
laptop class name and accessible values
it's just trying to call tostring which
is this it is written hey it's not going
for the superclass here
that is awesome now let me also try by
deleting this thing okay let's not call
to string by ourselves let's see if it
is getting called automatically it is
happening right now whatever you want to
return you can do that here right what I
want to return is I want to return the
model information with a
colon between and the price so that it
will print that particular data compile
and run you can say it says Lenovo Yoga
thousand dollars okay so that's how we
can basically work with the object class
methods if you don't mention it will be
coming automatically by the object class
now there is one more thing let's say if
I create one more object of laptop and
this time let's say the values are same
let's say this is object one object two
this is the object one one okay don't
give me suggestions yeah this is two and
two now if you compare these two objects
are the same yes the values are same but
do we have the objects which are same
let's try how will you compare this so
what I can do is I can just create a
Boolean variable here
and I can say result
is equal to how do I compile object 1
dot obija 2 or obision 1 is equal to
equal to Omega 2.
let's try I mean we can use double equal
to between obj1 and object 2 as well
let's try to print the result and let's
see what happens if I compile this code
and run
oh it says false okay maybe using double
equal to is not a good idea let's use
some inbuilt methods if you can see obj1
actually has a method called Equals it
checks for the equals okay that's great
it checks for the equals of obj1 and
obj2 okay let me try this I hope this
will work compile and run oh it is still
giving you false
why the objects are same right the thing
is if you go with the equals method here
you can see in our class we don't have
equals and the equals is actually coming
from the object class it basically
compares the two object by their hexa
decimal number we don't do that so we
want to compare them based on their
values so one thing we can do is we can
implement the equals method by ourselves
so we want the equals method which will
return a Boolean value the method name
is equals and it will accept only one
object I will say this as an object of
the same type laptop because we are
comparing laptop with laptop I will say
this is other and then the object which
is calling this equals is this object
and we have passed one more object here
which is other or maybe I can say this
is this and that so this is that object
this object so we are comparing two
objects
now how do I compare I can check if this
dot model dot equals so when you talk
about this model it's a string right now
string has equals implemented properly
so we can use string equals to compare
the string and this dot we are comparing
that dot model right we are comparing
two strings here and we have to also
compare the price this dot price is
equal to equal to that dot price now why
I'm using equal to for integer because
that's how it works right
and we have to also say open and close
if this matches then I will return true
as I will return
false
simple right and since we have only one
statement I can actually do this
right
in one line you can see I'm just
comparing the values here I'm combining
these two strings which is model model
and price and price
it will not use the equals of object
class it will use the equals of my own
class let's see if that works compile
and run oh it works can you see that we
got true now if I change the value let's
say it becomes yoga one
and if I try to compile and
then you can see it says false because
we have a different value
cool
okay in fact you know I can actually
simplify this more why to even mention
if else anyway this is returning true
and false right
what I can actually do is the entire
stuff from here
you can cut this part and say return the
entire string
because the string itself will compare
right it will return true or false
I can do that in one line
yeah this one way but there are some
rules in Java if you are trying to do
equals
when you when you say two objects are
equal of course they should have a same
value and they should also have a same
hash code so what I mean by that is
don't Define the equals and equals
method by yourself you can use your ID
and you can say
Source action and you can see it gives
you an option of generate hash code n
equals click on that
select all the variables which you want
to compare and click on OK it will
generate the equals method for you and
you can see it does multiple checks we
have only checks for the value but what
if you want to check if the object is
not null maybe you want to check for the
class name as well maybe you want to
check uh if the model is not null before
comparing so it does multiple checks for
you it's a it's a good practice
and that's why I say sometimes you have
to prefer your own IDE output and it
also implements hash code you know this
is how the hashmer is generated
basically uh it takes your data and
works and applies some algorithm on your
data to generate the result if this
algorithm can change you can Implement
your own algorithm but of course it
should have all the variables which
should come comes into play example
let's say I have one more string here
which is serial number
and I'm okay if two objects have the
same model number and same model same
price by different cell number that's
okay with me so maybe you can just skip
this serial in your equals and hash code
okay that's the important thing the
thing you have to remember here is the
object class has multiple methods and we
have worked with two string which is
here in fact you know we don't even have
to mention two string here we can right
click and we say
Source action generate two string with
both the variables okay it will generate
a two string for you which is much which
gives you a much better output than what
you can type
now I know with by asking the code from
your IDE you get these two extra
annotations here in fact three
this is actually we'll discuss that once
we talk about annotations at this point
is not needed it's not compulsion but it
has some importance which we'll discuss
later yeah that's how we can use object
class we can work with
hash code equals tostring and yeah in
this video we'll talk about what is
downcasting and upcasting now before
this we have to understand what is
typecasting so let's say we have a
double value so let's say double D is
equal to let's say 4.5 and then of
course I can print this value I can say
d and we all know what will be the
output it will print 4.5 but what if I
want to save this value somewhere okay
so example if I say int is I equal to D
can we do that can we have the double
value inside integer of course it will
not support right because 4.5 cannot be
stored in integer so yes we can at least
store 4 here right so maybe we can
remove 5.5 we can at least store four
but how will we do that by default Java
will not allow you that because Java
says I type mismatch cannot convert from
double to int it's because it says you
know uh you might lose data and we can
say hey that's okay for me I am okay to
lose data so what you can do is you can
Typecast it so you can say hey I don't
get what value you send just send that
in the integer format I'm okay with it
okay so this is typecasting you are
converting the type of a value right now
by doing this if I try to print I let's
see what happens of course we are
showing that integer we will lose data
so we are losing 0.5 but that's okay we
at least we got four now this is called
typecasting
now coming back to the world of oops can
we do this in oops so let's try and we
have talked about inheritance we have
talked about uh how can we have methods
into two different classes how can we
override those stuff now just to keep it
simple what I will do is I will create a
class here and we'll name this class as
let's say a again I'm just trying to
keep things as simple as possible we
could have gone with other other names
as well like calculate or something just
to keep it simple let's say we have
these two classes Class A and Class B
and Class B extends a so we are
basically trying to achieve in heightens
here
and now with this what we can do is we
can create object of a of course we can
do that right we can create object of a
and that perfectly works now in this two
classes I want to have some methods
let's say in a I have a method which is
show or maybe I will say show one and in
B I can have a method which is public
void Show 2 right and then I will just
print something here
so I can print in a show
and now you know what I would say here
see we can write any complex logic to it
right but the idea here is to understand
the concepts that's what you're focusing
so in B show now what I want to do is
using this a object so if you can see we
are creating this obj of type A and also
the object is also of a right and now
with the help of this obj and you can
see I'm not trying to achieve method
over writing here there are two
different methods so one show two two
different methods and I can call show
one and you can see I can only call so
when I can't call show two what's the
reason I can't call show two it's it's
very simple we don't have Shoto inside a
and a don't even know B exists okay
that's a fact B knows what a is but a
has no idea what B is I hope that is not
the scene in real world your parents
knows you so let's let's try this
compile and run you can see it says in a
show but now my question to you is
can I have the reference of a an object
of B and then we have seen that it is
possible I can actually create this I
can have a reference of a and object of
B we have done that in Dynamic Methodist
patch we can basically do this right now
what we are trying to do here is we have
an object of class subclass and then we
are trying to assign that to a pattern
class now we can actually say hey you
know what you can do please Typecast it
so whatever object you are sending is of
child class but Typecast it with a which
is a parent class
the same thing we have done for the
integer interval right now when you are
doing this we are basically going up
right which is if it if you try to
compare this A and B A is a super Class
B is a plus so we are trying to say
refer I mean objectives of B but refer
to a so we are going up which is up
casting so this concept here is called
up casting and of course this will work
there will there is no issue you can
still call in a show because in b as
well we got the same method even if you
have the object of B it will still work
okay so this is called upcasting so even
this is not compulsory it is something
which is which happens implicitly behind
the scene so you don't have you don't
have to mention the casting part it
normally works so this is upcasting now
what is downcasting
so let's say I'm creating a reference of
B now why we have to go for the
downcasting first of all see using this
even if the object is of B using this
obj I can't call show 2. if you can see
the object is of B and the method show
to belongs to B but still you can't call
it reason is because the reference is of
a and a has no idea what is this show
too okay so to solve that problem what
we can do is we can create a new
reference let's say obj1 but then I want
to use the same object I don't want to
get a new object of course you can do
this but you're getting a new object can
we do this can we say obj1 is equal to
obj now the problem is even obj is
referring to a new B object but the
problem is it is referred to a it's the
type of obj is a so it's the same
problem of double and int right similar
so what we can do is we can do a
typecasting here we can say hey I know
this is reference of a but the object is
of B right so whenever you use assign
fine I want the type to be of B and
that's how it works this is called down
casting so this obj is the parent object
or parent reference you are downcasting
it to the child reference Now using this
new obj1 I can call show two okay so
this is
downcasting this is downcasting this is
up casting in general they are called
typecasting okay
so you don't have to actually remember
this terms every time up casting down
casting at after some time you actually
you get used to this concept you will
implicitly use those things anywhere you
want
but yes while teaching we have to use
some words so upcasting downcasting so
yeah that's about this concept but
remember this we can create a parent
reference and child object and we can
also come back to the child reference
here in this video let's talk about
abstract keyword now what is abstract so
before that let's understand something
so we know what is class what is object
what is in items and how do we do
overriding of the methods right now with
those knowledge let's talk about
abstract keyword so for that what I will
do is I will create a class here and let
me name this class as let's say a car
okay now in this card you will Define
some methods let's say if you talk about
car a car can drive
of course right a car can play music as
well public void I mean that's what we
do right we play also we also play music
in the card you know some people they
don't start their car before playing the
music
or they don't start they don't uh set it
on a drive mode before uh before they
play the music okay so we have these two
methods let's say maybe we can add some
more methods in the car maybe you can
sleep in your car and other methods but
let's say we have this too we have drive
and we have play music and of course in
this method I can Define some statements
let's say when I say it is playing music
I can say play music or we can write
multiple statement logic is not
important the important thing is a
concept let's focus on that so let's say
in the play music we have this statement
and in Drive let's say at this point I'm
not sure I want to build my own car but
I'm not sure how can I drive a car I
know how to implement play music but I
don't know how to set up the engine I'm
manufacturing my own car so I don't know
how to set up the engine how to set up
the wheels but a car should drive that's
what I know and that's why it's we call
it right if you don't have a drive
feature then why you will call it a card
you can State it's a home theater anyway
now if I want to use this car I can
simply create an object I can say obj
and then I can call the methods I can
call both the methods opj dot drive and
obj Dot play music of course we have two
methods I should be able to call them
now if You observe in the drive we are
not doing anything why we are not doing
anything because I don't know how to
implement drive but I know how to
implement play music so I'm able to
create this object and I'm able to call
these two methods and I I think it
should work and if I go back and run it
works it's not like if you don't Define
something it will not work it's working
the only thing is when you're defining
this method you are actually not
implementing anything here you're not
writing any statements so it's valid in
Java syntax term but as a feature I mean
just imagine you're buying a new phone
and your phone says it can do this
feature this Feature Feature one feature
two feature three but then none of the
feature works of course you will not buy
any phone like that right in the same
way if you talk about this card you are
writing a method over here which is
drive when you're not implementing it
why someone should be able able to
create object of this why in first place
someone should create a class itself
right when you don't know how to
implement it see the thing is when you
build an application you have a
structure which you follow you design
your application not I'm not talking
about the thing you which you see on
this screen I'm talking about when you
build an application you design on paper
what are the classes you need what are
the methods you need now at this point
you know how to play music but you don't
know how to drive now in that case
should I remove this method completely
if I do that then how will you call it
as a car so what you can do is you can
say Hey you know I am creating this
method drive but I'm not sure what
should I implement it here so instead of
defining it here so when you open the
curly packets and close you are
basically defining a method so instead
of defining a method you can basically
declare a method which means you can put
a semicolon at the end when you do that
you are declaring a method that also
means that the drive feature you had
declaring but it is not working and no
one should be able to create object of
it okay again we'll see that in some
time but when I declare it it is giving
you an error now first of all why you
will declare when you are not defining
anything maybe I have this mindset
someone else can just come back and they
can say they can Implement a car maybe
they will build a a wagon let's say and
a wagon will extend my car and it is the
wagon's responsibility in fact you know
instead of saying wagon let's say wagonr
it's a very famous car if you search
online uh so we have this wagonal car
which some of them don't like not not a
big fan of it but
okay so let's say we have this card
wagonal extends card in fact I have a
card which is smaller than wagonr which
I love so we have this class wagonr
extends car here and what I want here is
I want this wagonard to implement the
drive feature see if you think card is
just an abstract concept right no one
actually buys a card what you buy is a
real car like wagonard or BMW GLS or the
Toyota Fortuner or Ford ecosport right
so you buy a real car you don't buy a
card this is just a concept so when I
say drive here a car don't know how to
drive but then when you when you create
a real car that car will know how to
drive so I want this wagonr to be
responsible to Define this method okay
so I can just copy this and paste it
here and here instead of declaring it I
will Define so what I want is I want
this wagonr to implement it of course
the other feature like play music can
simply be extended but not drive drive
should be implemented here and wagonr I
mean the company who built wagonal cars
it's their responsibility to define the
method here I can say driving of course
they will write a complex logic but just
to make it simple I'm writing one
statement so they are responsible to
Define this method and we are not doing
it here now if you want to declare a
method you can see we are getting an
error here you can use an abstract
keyword So when you say abstract it
means I'm just giving you the abstract
idea of a car should have a drive
feature but I don't know how to
implement it now when you are using my
feature and when you call your vehicle
as a car it should have a dry feature or
whatever object you're creating is a
card you need to have a drive feature
and that's how you make it so you make a
public abstract void drive so you have
to use an abstract keyboard if you want
to declare a method okay here we are
defining it but if you can see even if I
do abstract it is giving you an error it
says the abstract method Drive in type
car can only be defined by an abstract
class okay what it simply means is if
you have an abstract method abstract
method can belong to only abstract class
so that means you have to make this
class as abstract as well so you can
have abstract methods only in the
abstract class and whichever class is
extending the abstract class will have
this drive method if we don't do that it
will give you either example if I change
the method name you can see it will give
you error it says the typewagonr must
implement the United abstract method car
dot drive so if you are extending an
abstract class you need to Define it
compulsory otherwise it will not work so
you have to Define you have to basically
override the method now when someone
creates an object of a car in fact first
of all you can't create object of
abstract class Point very important
point and that's why you can see we got
an error here it says cannot instantiate
the type car it simply means you cannot
create object of car so the point
remember you cannot create object of an
abstract class okay but then connect it
to reference of abstract class yes that
is possible you can say car obj that is
absolutely correct but if you want to
create an object you have to get object
off not card but wagonr okay and then
with this object you can call drive you
can call uh play music and we have
talked about Dynamic method dispatch and
we know when you call drive it will be
calling Drive of webinar not of car
anybody is it is declared right uh so
basically that's how you can create an
abstract class that's how you can create
an abstract method and basically that's
how you can restrict the creation of the
object here now a few more points to
remember is it compulsory to have an
abstract method in the abstract class I
mean we know that it is compulsory to
have the abstract method you need
abstract class right but is it
compulsory to have a abstract method in
the abstract class let's do that if you
come in this section okay you can say
there's no problem it's not like a
abstract class should have abstract
method
abstract class can have abstract methods
it can have normal methods so you can
have an abstract class with which only
has abstract methods you can have
abstract class which has only
implemented methods which are this which
are non-abstract methods and you can
have a abstract class which can have
both normal methods as well as the
abstract method and you can create
multiple abstract method okay example if
I can come back here and say Hey you
know I want a car to fly I don't know
when this is possible but in the movies
you see that right so a car jumps from
one building to the building uh okay and
I hope you know the movie name but
anyway so if you talk about this
abstract method which is fly and you can
see I'm declaring it here now when you
declare a method and when you say you
have an abstract class which is getting
implemented or which is getting uh
extended by another class it becomes
compulsory for you to Define one more
method here so you can say public not
abstract you can say public void you
have to Define fly as well otherwise it
will not work so you can say a flying
okay and now with this you can call the
methods you can say obj dot fly and this
should work compile run and you can see
it says driving play music and flying
now there's one important thing here
which is what if when you are creating
this class wagonr and then you are not
able to implement fly what will happen
first of all it's compulsory to Define
all the methods okay all the abstract
methods so you can see in this class we
have three methods but only two methods
are abstract and that's why it says it
should Define fly as well as drive but
we are not implementing fly so you can
see it says the type again I must
implement the United abstract method
car.fly but what if you don't do that
so in that case if you have a class
which is not able to implement all the
methods in this case even this class
becomes abstract class so you have to
make it abstract class
and you can see there's no error but the
problem now is
you can't create object of abstract
class right so maybe you have to create
a new class here by saying uh updated
webinar which can also fly and this will
extend now which class you want me to
extend the car or the wagonr of course
wagonal right because you will get this
drive feature from a wagonr so you can
simply extend it with wagonr and then
here in this class you can basically
create object of fly in fact if you are
using IDE and if you don't if you are
lazy to type you can come to the seller
and you can say fix Quick Fix add
unimplemented methods and it will do it
for you okay and here we can say flying
so even you can do that the only thing
is now the object will not be of wagonal
the object will be of updated wagonr
is it the method class name okay it's up
it should be updated right so that's how
you can create a object so again we are
not getting object of abstract class we
are creating object of the class which
is not not abstract okay now since we
are calling this class as abstract class
even this class should have a name right
so normally we call them as a concrete
class so we can say this is a concrete
class
okay so we have abstract class and then
we have concrete class so you can create
object of a concrete class not an
abstract class so I hope this makes
sense uh that's about abstract keyword
so let me just reiterate abstract
keyword can be used with methods if you
want to declare them and if you have any
abstract methods you have to make a
class as abstract but again on the other
hand if you have abstract class there is
no compulsion that abstract class should
have abstract methods abstract class can
have normal methods also I mean all
these normal methods no abstract methods
even that is possible next Point
remember we cannot create object of an
abstract class if you want to create
object you have to get a class which
which implements all the methods a
subclass which implements all the
methods and then that class will be
called as a concrete class and you can
create object of it so that's about
abstract keyword in this video we'll
talk about inner class that's right a
class inside a class I know that sounds
weird at first but let's let me go with
that see most of the time when you build
an application you might have a scenario
where a class will be used only for that
particular purpose okay so let's say you
have a class A and then that class needs
variables so we can do that example we
have a class A here and this class A can
have variables this class can have
methods so when you have this class A
this class can have variables this class
can have methods right now this
variables and methods only work for this
class A so if you want to access them
you have to get a class first
in the same way let's say if you have a
class where that class is totally
dependent on Class A there is no other
need for it in that case you can create
a class inside the class
okay the way you do that is by defining
a class like a and then you can define a
class called B inside it now just the
way you have class A here I can create
variable that works we can say variable
age and then we can have method as well
which is public
white show now we have these two things
we have a variable which is age and then
we have a method which show and then we
have a class as well so imagine a class
having all three things a variable a
method and a class
and inside this class let's say I have
created I create a method which is
public void config and in this config I
will print something
let's say in config just to print
something okay and I'm trying to make
this example as simple as possible
that's why I'm using this class name in
real life don't do that make sure that
you use proper class names
and so let's say we have this scenario
now question is how will you call this
config so it's very easy to call show in
fact I should print something here just
to see what it prints
in show now question to you is how will
you call this show and then we have seen
this right you simply have to create
this object of a and then you can call
obj
dot show I mean show will perfectly work
right if I compile this code and run you
can see it says in Show Now I want to
call config how will you do that do that
of course you will say if it is a Class
B then you have to get object of B to
call this config let's try if I try to
create object of B by saying B obj one
new B you can see it will give you an
error it says
uh B cannot be resolved oh it's not able
to find B the thing is B is not openly
available right B is a part of a so if
you want to have a b here you need to
say a dot b so B belongs to a that's why
you have to say this
okay now why I'm doing this so when you
say if you compile this code and if I go
back here can you see that we got two
classes and we have seen this right
every time you compile a code you will
get those number of class files so
you've got a class file for demo that
makes sense you can see we have
demo.class uh you will get a DOT class
as well because uh a is a class but we
also got B is also classified it should
have its own class file and that's right
we got it we got B dot class the only
thing is B belongs to a so the dollar
symbol separates these two so it says b
class belongs to a class and that's why
it's a dollar B
okay that makes sense so if you want to
access B you have to say a dot b that's
how you access it and you can say obj1
you can say there's no problem in
declaring the variable the problem is
when you say new now how will you do it
if you say B it will not work again it
will say cannot able to resolve B in
that case if you say a dot b no that's
not the proper syntax the thing is if
you want to create object of B you need
object of a first
now you will say why it's very simple if
you want to call B if you want to call
this show now show is a method right
it's a non-static method which means if
you want to call show you need object in
the same way if you want to access this
variable age you need object in the same
way if you want to create object of B
you need object of a because that is a
non-static method okay so I'm focusing
but on static here right can I create a
static class uh yes we'll see that in
some time but we got this object Here
and Now using this obj1 I can call the
config method if you want to create
object of a inner class which is B in
this case you need to First specify
where it belongs to so B belongs to a
and then you need object of a outer
class which is obj here to create object
of inner class and once you have that
you can simply call this methods and
that will properly work you can see what
in show and in config okay now we have
all also focused on a study class right
you can also make this class as static
and we all know when you refer it to our
static class you don't need object so
basically you don't call this with the
help of object you can directly refer
with a dot b now this will work only
when the class is static the inner class
is static it will not work for
non-static class now can we really make
study class yes we can provide it there
it's an inner class if it is out of
class you can't make out of class static
you can see it will give you add it says
illegal modifier for the class A only
public abstract final are permitted so
basically you can't use static here
static can be used only for the inner
class okay I hope that makes sense so
that's the concept of uh in a class now
once we know about inner class let's
talk about Anonymous in a class I know
that sounds weird right anonymous
anonymous simply means something which
doesn't have a name okay so what I will
do is I will just try to remove
everything here and let's work with this
particular class okay and in fact I
needed a a class let's say class A is
there okay and inside this class A I'm
creating a method which is public void
show again just to keep it simple I'm
using simple names here and here I will
print in a show okay and if I want to
call a of course I will simply say A obj
you need to create object of a and then
I will say opj dot show let's see if
this works compile and run it works you
can see God in a show that perfectly
works now the question I have for you is
very simple question what if I want to
change the behave behavior of show
method okay that means I wanted to do
something else now I know in your mind
you have the idea right we can simply
create a class which is B and this class
B will extend a so basically basically
we are trying to do method over dividing
here in this B as well you will be
having the same method which is show
which will print in B show we just want
to do something else and by doing
something else what I mean by in this
code is I'm just trying to print
something else but of course you can do
whatever you want I just want to change
the behavior of this show method so we
created a new class called B and here
what we can do is we can create the
object of B but the references of a so
what we are doing is we are overriding
the behavior of show and then you will
say hey we have already talked about it
right we have talked about method over
writing hold on hold your horses let's
see if I compile this code and run it
says in Bay show but now if you think
about this class now first of all uh as
we mentioned every time you compile a
code it will create all the class files
see we got a B because of the previous
code let's delete that you can see we
got B dot class as well now you will say
what's a harm in that see the Harvest
the only purpose of this class B was to
extend or to extend a class to override
the method and maybe it will be used
only once now of course if it is using
multiple times in different places of
course it should create a new you should
create a different class but what if we
know that this class will be used only
once only for this particular use
in that scenario why to create a new
class oh then you will say if you don't
get new class how will you get a new
implementation okay let me show you
something what if I can simply come back
here just before the semicolon and I can
Define what should be the new
implementation
I know this looks tricky but just be
with me see till this point we have seen
that first you have to create a class
and then you create the object right and
that's what we are doing from a long
time but now this is the first time that
I'm saying I want to create object of a
but this is the implementation
this is the design for it don't go for
the original design I will give you new
design the new design is I will use the
same method name or same method here the
only change I want to do here is it will
print in new show
I will just provide some indentation so
that it will look better so what I'm
doing here is I'm providing a different
implementation for show method
okay and let's see if this works I just
want to see
compile and you can see that it says in
new show it is not going for the
original method
so we are providing a new implementation
here now this is called uh in a class
okay you will say hey how it's a class
we are not creating we are not using a
class keyword right that's why we are
not using that last keyword and we are
not even giving a name to it and that's
why it is a inner class because this
class is created inside the demo class
and also there's no name for the class
and that's why if you go back to your
files can you can you see this
we got demo inside that we have a class
but there's no name for it and since we
don't have a name for it it says one of
course if we create multiple classes you
will have a different number it will say
2 3 4 and list goes on
and since we don't have a name it is
called Anonymous class
so this is Anonymous in a class which we
are going to use a lot in the upcoming
videos uh once we talk about interfaces
must we talk about functional interface
Lambda Expressions this is very famous
concept so just get used to it now if I
if you want me to type this code one
second I will do that for you I will
what I will do is I will just go back
here
see it is not difficult it's just that
you are unfamiliar with this concept and
it will take some time
okay so what you do is just before the
semicolon and after the Constructor open
the curly packets and close this is your
class and in this class you provide the
method which is show and whatever you
want to do in show you can do that here
you can say I'm printing in new show and
then you can call this show so when you
call this show it will call the show of
the new implementation not this one okay
and yeah that's how it works so that is
your Anonymous inner class okay so we
have talked about abstract class we have
talked about inner class in fact we have
talked about Anonymous in a class can we
just use both let's try what I will do
is I will just make this class as an
abstract class because I want to create
this method show as an abstract method
okay let's say this is abstract
okay and then uh let's say I'm not doing
all those things
now I have a question for you if I want
to create a object or if I want to
instantiate a can I do that of course in
the abstract class we have seen we can't
do that because you can't instantiate
the abstract class and we have found a
solution as well you can create a
separate class by saying extends a and
then you can provide the implementation
here you can just go here quick fix
implement the method and one more thing
you might be saying that I'm reviewing
this line multiple times it's just that
we have not talked about what is at the
rate override will we have a separate
topic on that so at that point we'll
discuss that so here I just want to say
in the show okay and then of course I
can create the object of B and that's
done with the help of this object obj I
can call show again we have seen this in
abstract class concept
but I want to talk about something else
so you can say it says in B show
now if you look at the entire purpose of
this class B is to implement the show
method that's it and if you are using
this method only once then why to even
create this class can I use something
else can I use anonymous inner class
here okay so what I'm what I'm saying is
I can simply say new a
and okay it's not working but can I
provide the implementation here and I
can create a method which is public void
in fact I will just simply paste the
code because we already have that code
with me
and here I will say in new show so what
I'm doing is I'm providing the
implementation for the abstract class
here itself okay and you might be
thinking we are still getting new a
right is it the object of an abstract
class we can't do that right how we are
doing this the thing is this is a class
here right the anonymous in a class and
we are creating the object of not a we
are getting the object of this Anonymous
inner class
that's a point to remember
so most of the time when we have
interfaces or abstract class we use this
concept so if you want to implement uh
the interface or the abstract class only
once
then you can use anonymous inner class
and this perfectly works so let me just
try it out
compile this code and run you can see it
works so we can use anonymous in a class
for the abstract class as well
in fact if you have multiple methods you
can still do it if you let's say we have
one more abstract metal here which is
public void let's say config we can
create a method for config as well and
since we are using an IDE it give you
the method so you can simply use this
and you can print
in config so it's not just for one
method if you have multiple methods you
can provide the implementation in the
anonymous inner class
in this video we'll talk about
interfaces now before we start with the
interface let's talk about the abstract
class now let's say I create abstract
class here so if it's abstract class A
and in this class let me create some
methods now we all know in the abstract
class we can create our abstract methods
and normal methods as well but let's say
if I have abstract class which only has
let's say abstract methods if I say
public abstract void show and we have
public abstract void config now when you
have abstract class with two abstract
methods of course this works there is no
compulsion to have non-abstract methods
here or we call them as concrete methods
there is no need for them now whenever
you have a situation where you have
abstract class which only has abstract
methods we have another way of doing it
now see all these are decided at design
time so when you make an application at
designing you specify things okay what
are the classes I need and what are the
abstract class we need
so you create this hierarchy of system
of course we'll talk about hierarchy in
some time why do we need it but at this
point we create a hierarchy and when you
have a class which only has abstract
methods the other alternative for that
is to create an interface so instead of
creating an abstract class we can create
an interface
most short time we use this interface in
project development so let's understand
that so we have the interface a now you
will say what is changing there now
first of all interface is not a class
okay so that's why that's the main
difference between abstract class and
interface and by default every method in
the interface is public abstract so
these two keywords actually not required
because anywhere they are public
abstract so even if you don't mention
they are by default public abstract and
that's why if you can see when I put a
semicolon just after the method there is
no error because behind the scene public
abstract is there now this is your
interface so interface basically means
it's like a class just that all the
methods are by default public abstract
okay but then how will I use this how
will I instantiate this the same problem
was there with abstract class right we
cannot instantiate it now if you look at
this how do I instantiate let's try so I
will say a obj see there is no problem
in creating a reference of it so that
also also means we are creating a type
the way you create classes so let's say
if a is a class you can say a obj so a
is a type right in the same way here the
interface a is a type
okay this works but now I'm going to try
to create object for this
it will give you an error it says if you
see the error it says cannot instantiate
the type A because this interface you
can't instantiate it okay the what's the
solution
the solution is see first of all why do
we get interface we create interface so
that we can design something we can say
example let's say if you ask me about
how do we create a table I can say or
maybe if you ask me how to reach
somewhere so I can say go straight take
a right go straight take a right take an
auto uh take a bus get down at the next
stop so what I'm doing is I'm giving you
the path right I'm giving a design you
have to literally take a walk I will not
work for you I will just show the
directions in the same way interface
says I will tell you what are the
methods you need but I will not
Implement them it is your job to
implement so when I say yard now I'm
talking about classes see ultimately you
create object of a class interface just
show you the design
so here what I can do is I can create a
class let's say Class B so we have a
class B here and then in this class I
want to implement these two methods now
in terms of abstract class we say
extends right because class extends
another class here a is the interface we
have to use a different keyword here the
keyword which we use is implements so
whenever you want to implement the
interface you say implements keyword and
when you say implements it becomes
compulsory for you to Define both the
methods okay if you fail to Define both
the methods by default your class also
becomes abstract okay but we don't want
to get abstract class right we want to
create a concrete class we want to
create object of B in that case it's
your job to Define both the methods okay
there is one way you can use a shortcut
here you can just go back here and say
quick fix it will ask you to implement
the methods or you can do the hard work
you can say public void show and then
you can define something here I can say
I'm defining in show and then we can
Define another method as well which is
config or public
void config and here we can Define in
config so basically what you're doing is
you are implementing both the methods as
I mentioned before if you fail to
implement these methods or this class
becomes an abstract class but we are
implementing it right now when you
implement basically you can't create
object of a but you can create object of
B and you can say it works and now using
this obj I can call show I can call uh
what are the method we have we have
config so we can call both the methods
and that perfectly works if I compile
and run this code you can say it says in
show in config okay what else can I have
uh so the way you create variables here
also the way you create methods here can
I create variables now first of all we
don't uh Define variables right we
declare them so we can actually so if I
say int let's say eight that's a
variable I know I don't know why I'm
taking this age variable every time but
let's say we have eight age here and
let's say we have string area so that's
the area name
but you can see we got an error that
means can I I cannot create variables
that's weird I just said we can right so
the only thing is every variable in the
interface we can create actually those
variables the only thing is they are by
default final and static so all the
variables inside the interface are by
default final and static
okay uh so that means we have to first
initialize the variable So when you say
it's it's final we have to initialize
the variable right okay that's not my
age but let's say 44 and let's say area
is Mumbai
okay so basically what we're defining is
we are defining the age which is 44 and
the area is Mumbai now this variables
are final and static now first of all
since they are static which means we can
directly use the interface name remember
when we use static variable we don't
have to
use the object example if I want to
print the value of name or area here I
can simply say a DOT is the interface a
DOT area I can directly use it not with
the object
and if I compile and run it works you
can see we got Mumbai
if I try to change the value of this if
I say a DOT area is equal to let's say
if I want to change the area to
Hyderabad
it's not working you can say it says the
final field that's right the area is
final it is static we are using directly
the interface name and it's also final
okay so that's one thing you have to
remember now you might be thinking why
it has to be static final see first of
all you don't instantiate the interface
right whatever you instantiate is a
class and you are not doing extent you
are doing implements what you get in
implements is only the methods right you
don't get the variables there in
implements so that's why it is static
because we want to use the interface
name and final because interface objects
or interface don't have their own memory
in the Heap right what you create object
office of B not not of a
so if you don't have your own memory how
can you have a non-final variable so
this is interface in fact before talking
about the need for interface we have one
more thing to add here
so let's say if I have a interface and
I'm creating a class which implements a
one interface here can a class Implement
multiple interface example let's say if
I have interface which is called X so if
I say interface X so B Class implements
a and X both and the answer is yes if
you can see there is no error here the
only thing is whatever method you define
here so let's say the method name here
is run you can see we got an error here
the only thing you have to do is you
have to Define run as well so you will
say public void run so basically we can
have one class implementing multiple
interfaces now that's not the case with
abstract class right because in abstract
class we can we can extern only one
class in interface you can have a class
implementing multiple interfaces
so here I can simply print running okay
so what we are doing is we are using
multiple methods here we have three
methods coming from two different
interfaces this interface says two
methods show in config and this
interface is has only one method which
is one and you can see we got three
methods here uh there's one more thing
let's say we have one more interface
which is called uh interface y now the
thing is when you talk about class and
Class A Class can extend another class
right what about interface but can we do
interface and interface what keyword we
have to use here see whenever you have
interface to interface we say extends so
interface y extends X so inheritance is
is valid here as well now in this y
interface you will be having a method
called run so that's the inheritance
okay so you will get this declaration in
the interface y as well let me show you
if I remove this X and if I keep y even
now we have to use one otherwise if you
remove run from here if you you comment
this part you can see it will give you
error it says the type B must implement
the United abstract method one
okay but we are implementing y right
it's just that y extends X so we have to
use one
now Point remember here is whenever you
have a class to class we say the extends
whenever you have class to interface
basically a class is in implementing
interface so we have to say implements
and whenever you have interface to
interface we say that extends again okay
this is the point you have to remember
so again I will comment uncomment this
part
okay now there's only one thing you have
to remember whenever you create a
reference of a in phase and object of B
which is a class I can only call two
methods which is of part A if I try to
call run with a it will not work because
a has no idea what one method is if you
can see in a we don't have one in fact
what we will do is I will just remove
this code for time in yeah and then if
you want to implement one if you want to
call one in that case we need to create
the reference of X which is obj1 is
equal to Nu B now with this obj one I
can call one but again I can't call
other two two other methods okay so
that's one thing you have to remember
okay now once we are good with this
let's try to understand what's the need
of the interface let's try to understand
what is a need for the interface now for
that let's take an example here so let's
say we have a class here and so the
example which I'm trying to take here is
for the developers let's say when you
join a company of course as a developer
when you join a company you want to
write code right you want to build
application and if you have seen the
trend whenever you join a company most
of the company will give you a laptop to
work on and luckily if you get a Macbook
that's great so they give you a laptop
right so that's that's the thing right
if you want to work in a company let's
say if you go to our office and if you
want to work there you will say hey I
want a laptop so in this case let's say
you are a developer okay so I will say
you are a deaf right of course you're a
human but let's say you're a developer
and then as a developer what you do you
make applications right or maybe I can
say you write code I'll set the app you
you develop applications right now when
you say you are developing an
application of course you will say
coding okay you're building an
application here of course as a company
if I want to build a product I have to
hire developers now in this case let's
say if I hire a developer let's say
developer name is Naveen and then if you
say new developer and with this object
Naveen I can say Naveen dot Dev app
right so I want the window develop
application and if I compile this code
and if I run it perfectly works right
now let's say
if I say hey you know I will make an
application but I need a laptop first I
cannot work without laptop but we don't
have laptop right so what I will do is I
will create a laptop class I will say
class laptop and in this class laptop of
course in a laptop what you do is you
write code and I can say calling
right in fact what laptop when you say
code you it basically you code the new
compile then you run so you do all those
stuff right so I'm saying code compile
and run and now as a developer what I
want is if I if you ask me to write a
code what I will do is I will just say
hey give me a laptop so basically you
have to accept a laptop object here
that's right you can also pass the
object so this developer will say give
me a laptop and then I will write code
so here instead of saying this you can
simply say lab dot code right now since
you have a laptop object you can
basically call this method called code
and it will work so what I'm doing is I
got two classes here which one is
developer and second is laptop and
inside laptop class I have a method
which is code and then once I pass this
object I can simply code right now the
only thing is when you ask a developer
to write a code developer will say hey
give me a laptop so that means first you
have to create an object of laptop so I
was a laptop lap is equal to the new
laptop so we got a laptop object of
course every developer needs a different
different laptop object so let's say if
you hire five developers you need five
laptops to give them
okay I was a lab here now this should
work there's no problem if you can see
the code everything should look good uh
if I run you can see it still works so
basically we are saying code compiled
one so what you're doing is from the
main method you are calling Dev app
which is here and then you are passing
the laptop object okay so you're passing
this object here and when you accept
this object you're calling the code
method so it will call this code method
and you have to execute this part
everything works well right now the only
thing is do you really need a laptop see
in some companies they give you a
desktop right so if you go to the office
you they will have a desktop where you
have a monitor you have a desktop a good
desktop which works so why as a
developer you are asking for a laptop
what if company wants to give you a
desktop you can't say hey I cannot work
without laptop right you should be able
to work on any computer
so let's say you also get an option of
desktop there in fact in desktop as well
I can do the same thing but I will say
faster like desktops are always faster
than a laptop right so you can see when
you're coding uh it says code compiled
One faster because it works fast now
what if a company says hey you know I we
don't have laptops with us but what we
have is we have desktop our desk is
equal to new desktop and they don't want
to pass the laptop object so that when
the company says Hey Naveen you have to
work you have to make an application and
what we are giving you is not laptop we
are giving you a desktop now nobody will
say I can't work you can see Naveen says
I can't develop application because my
application only needs laptop you can't
do that so writing laptop here is an
issue
we can't do that right so how do we
solve this problem and that's what you
know when I was talking about abstract
class and interface I told you about the
design thing right so when you back an
application you have to make it more
flexible here we are what you are doing
is you're doing a tight coupling here
which is you are saying that developer
is dependent on a laptop no developer is
not dependent on laptop developer is
dependent on a computer a computer can
be anything your computer can be a
laptop a computer can be a desktop so if
you want to improve this example what
you can do is you can create a class
called computer okay and in this
computer class you can say public void
code and basically you know I want to
keep this empty because I don't want to
add a code because we don't computer
does not exist right it's just a concept
and I can say a laptop is actually a
computer so when you do that the
advantages in fact desktop is also a
computer so when you do that what
happens is now both this laptop and
desktop they are computer so when I'm
creating a reference of it so can I say
computer lab is equal to new laptop and
computer
desk is going to do that new desktop we
can do that right we can create a
reference of a parent class an object of
a subclass and that's what we are doing
here same thing can be applicable here
right as a developer you are focused
more on the computer not on laptop or
desktop the moment you do that you can
say everything is working there's no
problem here is because what you are
passing here is Dex desk right which
desktop basically but that is referred
as a computer and what you are referring
here is a computer there's no mismatch
here you are passing a computer
reference you are accepting a computer
reference but when you call code it will
be called based on what object you are
passing so basically we are passing
desktop object So when you say code it
will call the code of the desktop not of
the laptop let me show you so if I
compile this code and run you can say it
says faster that's desktop but now if I
pass a laptop let's say computer company
decided to send you a laptop and now
when you compile and run you can see it
says code compile and when there is no
faster here that means that's laptop
code
so that's how you design the application
right to make it Loosely coupled where
your developer object is not dependent
on the laptop or desktop it is dependent
on the computer any computer will do a
mobile phone also do because that's a
computer now there's one change
see if it if you look at this code we're
doing nothing right so instead of
defining it here can I simply declare
this and we know when you're declaring
it we can make it abstract and since
your method is abstract you can also
make your class abstract and problem
solved and that's the importance of
abstract class right you can create that
abstraction layer where you say we are
not working with laptop and desktop in
real world as well we do that right uh
sometimes we don't mention rows or
lilies or sunflower we simply say
flowers right we don't say apartment or
a villa or anything we say house right
so we try to generalize things in real
life in real in virtual world as well
it's good to generalize things instead
of specializing things there's one more
don't you think we can also use
interface instead of using abstract
class so we are using interface we don't
need public abstract the only change you
have to make is instead of using App
extends we have to say implements
and that's the beauty of interfaces
right
I know we have written a lot of code
maybe you have to watch this video once
again to understand and try it by
yourself that's when you will understand
the power of the interfaces and what you
are creating here is not the classes
reference we are getting interface
reference yeah and that's the importance
of the interface in this video let's
talk about enums now enums are named
constants which we create so basically
if you try to have some consonant
example you know when you talk about
other codes or if you have worked on a
networking concept so let's say when you
send a request to the server the server
will give you some status right if it is
accepted the request if it is rejected
the request or the resource not found
the four not four error so basically you
know we have these numbers for every
type of data you get from the server and
also we can have a name for it now when
you know that we have a specific error
codes or when you have a specific
constants which you want to use instead
of creating a different object by
yourself you can create are enum now how
it looks like let me just give you a
simple example so let's say we have enum
here and I'm saying I want to go with
enum of status so I will say status now
in this status I can have different
constants which I want to use now of
course you can create a class and you
can create multiple objects of it so
let's say this status can be of running
State a fail State success pending so
you can have all those things and of
course you can create a simple class
called status and you can create
multiple objects right but just to keep
it simple we can use enum where we can
Define all the names constant and they
said this is pre-built okay example
let's say if you talk about status I can
have status like running status I can
have status and of course you can if you
can separate them with the help of comma
you can say running then we can have
failed uh then we can have pending and
let's say success of course you can
change the sequence doesn't matter but
you can have this constant now the
advantage for this is if you want to use
an application where you want written a
status to the client uh that status can
be running the status can be failed
pending or success instead of getting
returning a string format or a specific
object you can simply return this status
now how easy it can be it's very easy
you can just go back to your main method
and you can say I want to have a status
so you can create a status reference
which is s let's say and this is same as
what you use normal variables example if
you want to say int I and then you'll
send the value as well right let's say
five so we have this int as a type then
we have this I as a variable and then we
have a value which is five in the same
way you can have a type as status that's
right this is a type of it so all these
are objects now this is something
different in Java now if you're coming
from C plus plus in C plus plus we
directly create these status and we have
all these constants
and it treats in them in a different way
but Java says oh everything is classier
so basically the status is a class here
I know that sounds weird but yeah that's
how it is implemented this is a class
and all this are actually objects of
status so by default you got you got
four objects and you can use any of the
object here example I want to use let's
say a status
dot running now that is my object which
has been assigned to S now of course you
can print this SEO and it will print the
running status so I can say compile and
run you can say it says running so
basically you can use any status here
now what are this just to reiterate
these are actually named constants so
instead of using numbers or string we
can use named constants it will make
your work bit easy again I'm not saying
you have to use this everywhere but if
you have a scenario where you want to
use constants uh we can we can use this
concept and you can use any constant
here we are using running I can also use
failed even that works compile and run
you can see we got a failed status but
yes if you try to use a status let's say
no idea status now if you can see this
status don't have any no idea and that's
why you can see we got an error here it
says no idea cannot be resolved or is
invalid field that's right so you can
only use those status which you
mentioned here now in other languages we
have one more thing you know all this
actually has a number uh so basically
you get numbering for it maybe one two
three four so that you can pick this
state as based on numbers in Java it
starts with zero so this is zero one two
three and if you want to get that you
can actually do it so you know you once
you get the status you can use a method
called ordinal so so different constants
here have different numbers this is
based on the numbers right or the order
of it so this is first second third
fourth right but when you have zero one
two three so when I try to create the
ordinal of running of course it will
point zero and that's what you want to
see so you can see we got zero but yes
if you change it to success which is
three in this case you can say we got
three in fact you know you can also
print all what if you don't want to
print one you want to print all here uh
so what you can do is instead of getting
one status you can get all the status
first of all because if you say status
doc success it will only give you one
status but what if you want to get all
so in that case instead of saying this
you can say status dot so there's a
method here if you can see we got values
and that's right why we got methods is
because this status is a class and you
get some inbuilt methods now from where
you are getting these methods we'll talk
about it in some time or maybe maybe
next video but uh you got methods so you
can see status dot values will give you
what okay so let me just jump to values
just to see what it will give you so
status dot value will give you an array
you can see it gives you an array so on
this side we have to say this is not a
normal variable this this is a array and
for that maybe I can say SS just to have
a different name and once you got this
array you can print all how you can just
come back here you can print all let's
try I'm not sure if you can get all here
no compile time issue run or it is
spending the address or something I know
that
okay so what you can do is you can
specify the index value I can say 0 it
will print running yeah it works but
then what if you want to print all and
we have seen it right we can use a for
Loop here now which one I will use
enhanced for Loop so I will just cut
this part I will use enhanced for Loop
here and every time you iterate of
course it will give you status right so
what is this added this arrays of type
status so it will give you one status at
a time so you can say status s colon SS
and here you can print the status so
basically it will print
all the status for you so you can say it
is printing all the status now with this
s you can also print the order of it
just to see how it works so you can say
s dot ordinal it will print yeah so it
will also paint the order of it 0 1 2 3.
yeah so let's expand our example of enum
with if else and switch now as I
mentioned before these are constants
right so basically when you have this
constant can we just compare them we can
actually the way you compare normal
variables or strings so let's take an
example here let me just remove int
variable there and let me also remove
the array let's keep it simple now so
let's say I have a status here and S is
equal to and the status of which I want
to set is let's say uh pending okay
initially the state value pending and
this value can be coming from anywhere
maybe you called a method which returns
this success or this status and you want
to check what is a status and based on
that you want to print some value
example if it says running I can print
all good if it is failed I can say try
again if it is pending I can say please
wait if it is success I can say done so
how do I know what is this value for
that you have to compare right so you
can say if the S is equal to equal to
status start running if this is a status
I will print I will come back here and I
will print all good and I can say if
else I want to check for the second one
I will say if status dot uh if it is
matching with failed I can print try
again else if if the status is equal to
I mean s is equal to status dot let's
say pending now in this case I can say
please wait else of course you can also
do if else else here but we only are
left with only one status I can say else
I can print done okay so basically you
can actually compare the status with the
help of if else and we can just come
back here say compile and run you can
see it works it says please wait because
this is pending but what if you got a
status which is a running state in that
case it will print all good okay so this
is how basically you can work with if
else but what if you want to work with
switch because say in switch there is a
limitation which now a switch can
support right it supports integer string
and many more but here the question is
does it support enum and the answer is
yes so what I will do here is instead of
using IF else I will just reuse the code
but I will use a switch here and in this
switch you can pass this status as it is
there's a change compared to if else
which is when you say case you know in
if else you basically have to use the
status as well but in case you don't
have to do that because anywhere the S
is of type status right so it knows
whatever your passing is basically a
part of a status so you can directly use
the constant itself so I can say running
if it is running I can just print this
statement and of course in switch we
have to also put a break and then we can
check for the second case
so that's case uh failed and here we can
have try again so of course we have to
say break here as well what else we have
two more
anyway let me just delete the entire
stuff from here if part you know I'm so
lazy I can just reuse this so the next
status is what pending in pending I can
say please wait and then the last one is
success in check for Success yourself
even writing the case we can say default
and here we have to give a colon and we
have to say done so basically whatever
we have done with if else we can also do
it with switch and switch actually makes
much more sense here because we are
working with constants right so switch
looks good in the case of enums and now
the question is will this work let's try
compile and run it works you can see it
says all good but yeah if I change the
status to let's say success I just want
to see if it prints done
yeah we got done so this also works with
uh switch so that's how we can use
with enum if you
if it enum and I've also mentioned that
enum is a class right so does that mean
we can extend any other class uh the
thing is no that's that's a thing which
is not suitable here you can't extend
enum within any other class apart from
this everything is same that means you
can Define methods you can Define
Constructors
that's right you can create Constructors
you can also create your own variables
inside the enum and that's what we are
going to do here
okay so what I will do now is and
there's one more thing is remember with
enum we have use certain methods for
example if I come back here and if I say
uh status was the object s okay here
let's do it here so if I say s dot you
can see we'll get some methods here and
we all know that by default every class
in Java extends object and that's why
you will get the hash code and then two
string Methods which is here but what
about this methods ordinal uh name and
then uh compared to now from where you
are getting all these methods so by
default enum in Java extends our
enumclass okay let me just prove that to
you I will just print it here s dot get
class
dot get
so what I'm doing is I'm just print I'm
getting the class name and the super
class of it so I'm just I'm just trying
to print this super class of our class
enum and I will just compile and run you
can say it is enum so inum in Java
extends E M class and all those extra
methods you get it from enumclass okay
now once we are good with this let's
treat our own class as enum and I will
do a different example here instead of
using status I can let's try to use
laptop because we have to use some
Constructor stuff which makes much more
sense with the laptop and let's say we
have some laptop models which I which I
love uh example MacBook then we have
Dell XPS
then we got surface not a big kind of
surface by little surface the Microsoft
laptops and we have ThinkPad I used to
love ThinkPad when it was with IBM but
anyway
let's see right and then what we can do
is let's say for every laptop I want to
define the price as well now how can we
do that so what we can do here is just
after this MacBook because that's an
object right so just after this I can
say hey Macbook will cost you let's say
two thousand dollars uh XPS will cost
you around let's say uh two thousand two
hundred dollars Express a bit costly and
surface is let's say 1500 I'm not sure
the cost and let's say ThinkPad is
eighteen hundred dollars so we got this
cost for this laptops here right and
then okay it gives you an error but
we'll solve that error in some time now
first of all what is that error so we
are trying to say that this is a price
but how will your enum will know that
you're talking about a prize here now in
this case what we can do is let's create
a variable int price so that we can have
an instance variable and then if You
observe here don't you think this is a
Constructor you can say it says that a
Constructor of laptop that's why we can
have a Constructor here so when you
create the object by passing a value
that's what we are doing here we are
saying these are the objects we have
and this is a Constructor where we are
passing a value
okay that means I can simply ask my
editor hey you know I need a Constructor
here which takes the price
and yeah we got a Constructor and now
you can see there is no error that means
whatever value you're passing here will
be assigned to this price and the beauty
is this laptop is a class and all these
are objects and every object will have a
different value for the price it's not
like once you define price for one
object it will be applicable for all no
that's not the case and once you have
this let's get back to our main and here
let me create a laptop lap is equal to
and let's say by default I maybe I want
a Macbook here and once you got the hold
of MacBook I can let's say I want to
print I want to print lab which of
course it will print MacBook let's try
once
yeah it plays MacBook I also want to
print the price of it oh now that's
tricky because the price is private and
we have seen that make make sure that
your variables the instance variables
are private how to access this now one
way to do that is with the help of
Getters and Setters the only problem is
can we use them here yes we can create
our own methods so what we can do here
is I can right click and I will say hey
I want a Getters and Setters basically
you can change the value as well okay so
that means if I want to print the price
I can just come back here and I can
print lab dot get price now this is
specifically for Macbook so if I use a
different object here I will get a
different price and with that if I try
to compile and run you can see we got
two thousand now what if you want to get
all the laptops okay let's try so we'll
just comment these two sections first of
all you need to get all the laptop that
means you need arrays so it's the
laptops or in fact you know what you can
do you can directly use a loop here and
you can say laptop lab colon from the
laptop so this is the enum you want all
the machines or all the constants so how
do we get all the values so dot we have
seen this right we can use values here
which will give you the array and one by
one you can fetch the value
so what you can do is you can print the
object and also you can print the price
let me print the price how do I get the
price it's a lab dot get price
okay I hope this will work let me just
verify once yeah we can do that so I'll
say compile run you can see we got all
the values and at any point you can
change the value as well okay so you try
that so try to call set price and pass a
particular value here and your price
will change okay there is one more thing
uh what if I don't specify the value for
surface let's say we have a surface here
and then I don't mention this value now
what will happen you can see we are
getting an error
why before it was working the thing is
see by default we have a default
Constructor right the moment you mention
a parameterized Constructor it says hey
if you want to get a constant you need
to set the price now because you have a
parameterized Constructor there is no
default Constructor here
so you can say okay I know how to solve
that you can create a default
Constructor here so you can just right
click and say Source action yes I want a
Constructor without the price okay and
you can see we got a default Constructor
here and it's your choice if you want to
specify some price here so you can say
price is equal to let's say minimum five
hundred dollars you can specify those
things and now if you can see the price
for surface will be 500. even if you
don't mention you will get a default
Constructor and the beauty is you create
four object it will call the Constructor
four times this Constructor three times
and this one once let me just prove that
point I will just try to print something
here I will say in laptop and let me
also print the object name itself I can
just say Okay this dot so we got a name
here let's try to see if this works
compile and run okay so that we got the
name as well so it says in laptop
MacBook in laptop XPS in laptop ThinkPad
but not surface is because surface
because it was created with the help of
default construction we are not printing
anything there okay so that's how we use
it and and mind you we are using it as a
private Constructor not a default or the
public it's because we are creating the
object in the same class itself and
that's how the private Constructor works
you can create the object in the same
class
in this video let's talk about
annotations now annotation simply means
a supplement to the Impala or to the
runtime or we also call it as a metadata
so basically what happens you know when
you write a code sometimes you want to
interact with a compiler by saying
something of course it will not change
the way your code will work it's just
that we want to supply some extra
information to the compiler or to the
runtime
how do we do that so let's say uh we
will go for a normal class here so let's
say we have a class A and then we got a
class B so basically I'm trying to go
for method over writing here so of
course we have to extend a class and
then uh this will have a method which is
show and then in this show I'm printing
let's say in a show and the same thing I
can do in a b as well the only thing is
we have to change it here now what we
are doing here is we are overriding the
show method of a with the show method of
BM then we have seen this before right
okay let's create the object of B just
to understand this so I will say b o b j
equal to new B and then I can call obj
Dot show and we all know what will be
the output uh so if I compile this code
and run you can see it says in B show
perfect now let's say I change this
method name okay not sure but something
else I will say
show the data which belongs to this
class okay so normally in Java we give a
meaningful name to a method right and
sometimes your method name can be big
and yes okay I know this is exaggerated
but sometimes you do have a big method
names with two or three words or four
words and then of course if you want to
override this particular method we have
to type the same thing here so I will
say the data which belongs to this class
okay so again I'm just trying to
override the method of a class with the
method of b class right and of course we
have to call this now so I will just try
to get it from the suggestion okay so if
you can see I'm just trying to call this
method
method because we have overed it in the
method so it should call in B sure right
so if I compile this code and if I run
this code oh it is printing in a show
now we were expecting in B Sure in fact
I wanted in B show but we got in a show
now this type of problems in programming
is called Bugs okay uh bugs are simply
logical problems where you are expecting
something else and you got something
else example you want to say two plus
two and the output is 4 but you got five
that is logical problem it's not a
compile time issue it's not a runtime
issue it's The Logical it's the logic
which you have written is wrong
and one of the most difficult problem to
solve is logical problems you know we
always say in programming that you know
you spend less time in coding and more
timing debugging that what is happening
here so of course you have only two
classes here and it is easy to debug but
if you have a lot of classes it will be
very difficult now how will you debug of
course we are trying to call the method
of b class but we got the method of a
class right how would you solve this
problem so let's try to understand the
method name on purpose I change the
method names okay I know it might be
visible for a few people you can see it
belongs here we have S in this method I
don't have it and sometimes you can miss
it right and then when I'm calling it
I'm passing s on purpose I was calling
the method of a class this type of
problems can arise when you write a code
so what you do is you can show your
intention to the compiler and compiler
will help you here of course right
whenever you make a mistake compiler
gives you error and looking at the error
we can easily understand hey I did
something wrong and let's go back and
solve this so what if you can ask your
compiler hey compiler you know what I'm
doing here I'm trying to overwrite the
method here of Class A and if it is not
happening let me know so you can show
your intention and you can show the
intention with the help of annotation
there are a lot of inbuilt annotations
available in Java so one of them is
overdrived so you can simply use add
rate here and you can say override now
you are saying by doing this to your
compiler hey you know I'm trying to
override the method and your compiler
says you know what there is no method
called show the data which belongs to
this class in the a class and then you
will know oh I made a mistake and then
you can solve this problem just by
putting s of course you can compare
these two methods and you can say I got
the problem so of course you have to
solve the problem so compile is helping
you by showing the problem right at
least you got some help and solving the
problem at compile time is much better
than solving the problem at runtime or
when you deploy the application to the
users and then users will give you a
prompt hey you know you made a mistake
so let's avoid that embarrassment and
let's solve the problem at compile time
so at overnight is one of the way you
can do that and now if you try to
compile and run you will get in Bishop
now apart from this override we have
different annotations as well uh which
we normally use in terms of core Java we
don't use most of the annotations of
course you can create your own
annotations but in general we don't use
much now once you start working with the
Frameworks example uh when you talk
about hibernate framework or spring
framework at that point it is mostly
driven by the annotations now there are
some annotations which works on the
methods there are some annotations which
works on variables there are some
annotations which works on class level
so example uh there might be some
annotation which you will be using on
class level example if I say deprecated
now this is one of the annotations we
have now what we are saying that we have
this class A deprecated simply means you
can use it but don't use it it is
deprecated soon it will be removed from
the Java language or there is a better
alternative for this so you can mark
your class as duplicated so that if
someone tried to use your class they
will get to know that this class is
deprecated
now apart from this you can also use
okay these are all class level
annotations in fact we are going to see
one mode when we start with interfaces
okay so if I try to use something on the
method level let's see what we have so
we have safe varrogs for the variable
arguments we have suppressed warning if
you want to hide the warnings once we
start with hibernate framework we'll
also say transient a functional
interface we are going to see in the
interface concept yeah uh in fact you
know when you create your own
annotations we can also set the
retention so example let's say whenever
you use an annotation till what level
you want to set it do you want to set
for compiler level that simply means if
you set a detention for compiler it
means once the code is compiled The
annotation will not make any sense after
that but if you say annotation is
applicable for runtime as well so after
compiling as well when the code is
running at that point also The
annotation will be applicable
so we have different options there and
of course this will make much more sense
once we start working with Frameworks
so yeah that's about annotations and uh
so we have different annotations and
remember when we were doing method over
writing and if you ask example let's say
if I remove this part and if I ask my
idea to generate a overnight method so I
can just go back here and say override I
want to override this particular method
by default it will give you at override
okay so that's you have to remember now
let's talk about functional interface
and we know the functional interface is
an interface which has only one method
so let's let's create one so what I will
do is I will create the interface here
and I will call this interface as a okay
and in this interface let's create one
method okay only one method so I can say
public abstract void show and public
abstract is optional so we can simply
say void show right and then I can
implement this I can use the I mean how
do I create the object of this of course
we know we can create a class we can
implement this interface and then we can
create the object of it right now this
interface is called a Sam which is
single abstract meta interface or we can
call this interface as functional
interface and to specify that this is a
functional interface we can use an
annotation which is a functional
interface by doing that we are making
sure that we only have one method here
okay see if I don't mention functional
interface and my intention was to have a
functional interface but if I if I write
one more method here which is one okay
there is no error here and we want
errors right
so if you have an intention of creating
only one thing I mean single abstract
method interface which is only one
method and then by mistake you return
two methods here you want compile time
errors right so if you write it
functional interface you can see it will
give you error it says invalid
functional interface annotation a is not
a functional interface so it's good to
specify The annotation here by
specifying a function interface but then
why we are giving so much importance to
functional interface we'll understand
that in next video but let's say let me
create the object for it okay now of
course I can't simply create a obj equal
to new a that is not possible because we
cannot instantiate the interface we can
do one thing we can create a class here
called B we can say B implements a and
we can basically Define this method
which is public void show and then here
we can print in show of course you can
do anything here but just to keep it
simple I'm saying in show and now
instead of creating object of a I can
get object of B which is possible right
and then I can call all obj dot show
this is one way the another way of
implementing this is we have already
seen which is Anonymous in a class so
what I can do here is instead of using
this class here I can just remove this
entire stuff or maybe I can just comment
this part and I can come back it by
saying Hey I want to instantiate a by
defining its own implementation here
okay in fact if I just say enter it will
back it's open close okay so you can do
this and then here itself we can Define
the method which is public void show and
you can Define whatever you want to do
which is in show so what we are doing is
instead of creating another class we are
using Anonymous inner class and we know
how to use this right and then I can
print uh show here let's see if this
works compile and run you can say we got
in Show
now since it is a function interface uh
now we are talking about Java 8 features
so till this point everything was good
till Java 7. now in Java 8 they have
done something awesome you know they
made sure that Java is no more verbose
now what is verbose means is specifying
everything making a detailed code it's
good most of the time to read the code
but sometimes you know you need to
shorten the code to reduce the number of
lines to reduce the bugs and all those
stuff so in Java 8 we got this amazing
feature called Lambda expressions and we
can use Lambda expression only with
functional interface now let's try to
use Lambda expression here so what we
are doing is we have a functional
interface and then we have discussed
about it function interfaces interface
which only has one method and then we
were able to instantiate a with the help
of a Anonymous in a class
and yeah we were able to call the method
now how do we use Lambda expression here
now Lambda expression says we just
simplify the anonymous inner class okay
only for Lambda expression now see if I
tell you okay just try to imagine this
if I tell you that there's an interface
called a and there's a method called
show so in your mind you know there is a
interface a which has a method show and
if I ask you to do this if I say try to
complete the sentence if I say a obj
equal to now in your mind you know a obj
equal to means there should be new a
round bracket 30 packets open and then
public void show now how you know that
this is new a because it's a object
right we're trying to instantiate the
interface here of course you can't
instantiate the interface but we're
trying to instantiate the class of
interface here a class which implements
the interface so basically when you say
aobj this is something you can imagine
right there is something you can think
about in the same way now since you're
talking about the interface a which only
has one method you also know that the
method name is show which returns
returns nothing it's avoid type and it's
also public by default so from here till
here you know it right so if you know it
even Kampala should know this right why
you as a programmer need to type this
code what if Java says hey
don't worry I'm there you just don't
have to type all those things you just
say back it open I will understand what
you're trying to do the only thing is
you have to put that uh Arrow here
that's it this is called a Lambda
expression this Arrow here is a Lambda
okay and this is the entire expression
we have okay so just to redo the same
stuff what we are doing is we are
removing from here
till here and since we are removing this
one curly bracket here we have to remove
this one as well so first let's remove
that Curly bracket and then we'll remove
the entire part from here and then we
have to put a arrow so by doing this we
are asking our compiler hey I will not
type the code I will simply say aobj
equal to it's your job to complete the
sentence see behind the scenes a
compiler will do it for you it's there
behind the scene new a public void show
is there it's just that syntactically
the code is getting reduced this is
called a syntactical sugar right where
you are reducing the code okay so this
is how it looks like and also if in this
method you only have one statement so if
you have multiple statements you need
curdly packets but if you have only one
statement you can skip that as well if
you can skip this semicolon as well
because it's not doing anything
and you can write everything in one line
and look at the beauty you can reduce
the code just like that and I know you
still have that doubt in your mind will
it this work let's try
and it's working you see that this is
Lambda expression okay can we do
something more with this of course I
want you to re-watch this video The
Cutting part and try it out now let me
can we do something else here what if
the show method actually accepts a value
which is let's say int I okay and then
from here also you have to pass the
value the only problem is how will you
accept the value here now instead of
making the changes here what I will do
is I will just go back to our previous
syntax so that I can show you step by
step what we are doing
okay so again I'm passing a integer I
here and then we have to pass the value
here now this is not a method which is
not taking any parameter this we are
taking a parameter so I have to accept
it here as well so you have to say int I
on any variable it doesn't matter and
then whatever you want to do with that
variable that's your choice let's say I
want to use it it's your choice if you
want to use it or not but I'm printing
in show I the value whatever the value
of I is which is 5 in this case let's
try to run this code to see is it
working yeah it is working you can see
we got five now can I use a Lambda
expression here and the answer is yes
what you can do is again from here till
here we don't need that and we can
remove the study packets as well the
only thing I have to do is you have to
put a arrow here we don't need this
semicolon we can just put everything in
one line and that's what we have done
and yes if you even if you have
variables you can do that not just one
variable if you have multiple variables
uh you can put multiple variables here
let's say a into J as well and then here
also you can accept into J just it's
just that you have to pass two values
let's say five and eight we're not doing
anything with J but it's your choice if
you want to use it or not as of now we
are working with only one variable so
let's
stick to that let's pass only one value
and let's write only one let's see if
this works compile and run it works you
can see that we got in show five so
there's one more thing
you don't even need to mention the type
of the variable you know why is because
we have mentioned it here right when you
know that the variable type is end why
to mention it okay
and one more thing if you have only one
variable you don't even need this round
brackets you can simply mention the
variable name here
oh we have reduced the code so much
okay so let's try to compile this code
and run it works right now let's do
something more with this now let's say
what if you have a method which returns
something what if you have a method
which accept multiple values so let's
try to do the example for that in the
next video but if you see the files here
okay this is the older one let me just
delete all the class files
just a keep it simple delete and let's
recompile the code here compile the
moment you compile you can see it is
creating only two files a DOT class and
demo.class of course behind the scene
there is anonymous class but it is not
creating a class file for you so it's so
it saves the amount of files which you
create of course the demo.java file will
be quite heavy now if you compare the
file size before using Lambda expression
after using Lambda expression the demo
file size will increase but it will not
create a new file okay so let's files to
manage okay so that's how we use Lambda
expression here so let's try to create
some more methods which returns
something else so let's say instead of
creating show let's work with ADD which
returns a integer value it will take two
parameters and I and in J right let's
say we have this and even before we go
with the Lambda expression let's try to
create normal objects I will say a obj
equal to new a and then you can also go
with the creating a different class or
we can go for anonymous class now we are
used to it right and the method name
which is public int add which accepts
two value into I comma into J and now
you want to return I plus J right of
course we can create a different
variable we can add we can return but
again just to reduce the number of lines
we are just saying return I plus J okay
and then once you have this we can
simply
uh take the value in result is equal to
obj dot add and we can pass to values 5
comma 4 okay
and then we can print result
simple stuff right now if I go back here
and if I see if this works compile and
run you can see we got nine so this is
working
now can I use a Lambda expression here
let's try so first of all let's remove
the entire part here this is not needed
and since we are removing this curly
brackets we can remove this one as well
so remove
and remove and then we just have to put
a arrow here okay just missed one
semicolon okay so one more thing as we
know that this is optional I mean we
only have one statement right so we
don't need to put curly brackets so we
can remove that one as well things are
working
okay let me just run this before
removing it to see if everything is
working compile and run oh it's still
working and now I can do one more thing
we can remove this curly packets
now we can write everything in one line
as you can see there's one thing
whenever you have one statement and that
to the statement is return you cannot
write return just return so you have to
remove that as well
so whatever you mention here actually
becomes height and type okay so when you
have one statement which is returned
which is an expression you can see I
plus Json expression it becomes a
written type
a written value
one more thing you can remove this ain't
and int as well
and you can see the code is so small now
and that's the beauty of Lambda
expression and one more thing so let's
say if you are calling a function or the
method by passing the object you can
also pass the Lambda expression in fact
once we start with the topic of
collections we'll see that how do we
pass the Lambda expression as the
argument okay that will be quite fun so
yeah so even if you have a method which
returns a value you can still use a
Lambda expression there so some points
remember Lambda expression only works
with a functional interface if you don't
have functional interface it will not
work because if you have multiple
methods let's say add and subtract both
and when you write this type of line
which method you're implementing is it
add or is it sub that's the confusion
right and that's why it is not allowed
so Lambda expression Works only with the
functional interface
so yeah that's about a function
interface which has a method which
returns something in this video let's
talk about different types of interfaces
so when you talk about different types
what are the options we have so
basically you know we can divide the
interfaces so we'll say type of
interface we can divide interface into
three parts okay the first one can be we
can call them as normal interface the
second one is your
functional interface and the third one
is your marker interface now this
functional interface is also called as
Sam so why it is called sample discuss
in some time but let's talk about
interface here now when you talk about
interface at this point we know that in
interface we can only declare methods
right
other thing is after Java 8 we also got
an option of defining the method in the
interface but we'll do that later at
this point we only know that in the
interface we can only declare methods so
all the methods and interface are public
abstract right now whenever you create
the interface which has normal interface
where where you have multiple methods it
is called a normal interface so example
if you create a interface here and let's
say the interface name is ABC and in
this interface if you have two methods
or more that is normal interface so
whenever you have an interface with two
or more methods that's normal interface
and by doing this you might have guessed
it right what could be the function
interface now basically before talking
about function interface let's talk
about Sam now Sam stands for single
abstract method okay so that simply
means if you have the interface and
let's say the interface name is ABC
again and in this interface if you have
only one method that is called a single
abstract method interface which is Sam
and we can also call it as a functional
interface now why this called functional
that we'll understand in the next video
when we talk about function interface we
have a separate video on that and next
twin we have is a marker interface now
what is Mark interface a marker
interface is an interface which has
no methods that's right a blank
interface now why someone will create a
blank interface is to update something
to the compiler so let's say if you want
to talk to a compiler by saying please
allow this example you know uh in Java
we have this Concept of Civilization
which means you can take the object and
you can store the values of the object
in your hard drive let me repeat you can
take the object let's say object has
multiple values so we can create let's
say in your HEAP memory okay I will do
that here so let's say in your HEAP
memory you got an object and this object
has different variables a b c and this
has some values let's say a value is 10
B value is 20 C value study and then if
you want to save this data in the hard
drive let's say we have a hard drive
here and if you want to store this data
we can use a concept of serialization
and then you can destroy this object the
thing is why we are saving these object
is because what if you want to recreate
this object later so let's say when
you're playing a game and when you're
playing this game you want to save the
game now now when you save the game
let's say when you're playing this game
the game takes around 4GB or 5gb in your
RAM but when you save the game it will
not consume that much of memory right it
will consume around in KBS it's because
when you restart the game after closing
it of course when you start the game you
will get a default values now if you
want the old values you want to resume
the game you will simply load the
current stats so let's say after some
time you close the game now game is no
mode but you have a file in your hard
drive and now you just started the game
the value for ABC will be zero zero zero
what you can do is you can load these
values from here now this is called
deserialization so this is
serialization and this is
deserialization okay now by default
every object is not allowed to do that
so it is not allowed okay you have to
give the permission how will you give
the permission so you can simply create
a class and you can give the permission
with the help of Market interface so we
have a lot of Market interface in Java
uh serialization or serializable then
when you talk about the advanced part
also we have some interfaces but it's
it's important okay so whenever you see
an interface which is blank that's a
marker interface and maybe in the
upcoming videos when you talk about some
Frameworks we'll talk about different
marker interfaces but that's what it is
uh so what is normal interface which has
more than two methods or two or more
than two methods the functional
interface or Sam only has one method now
this is actually important for the
upcoming videos and try to understand
this every time you have an interface
which has only one method uh we can use
some extra features with it in this
video we'll talk about
exceptions so before you understand
exception we have to first understand
different types of Errors so basically
when you talk about errors we have
different types for it the first one is
your compile time error now what this
errors are the second one you have is
you have runtime errors and the third
one is logical error now how do we
describe this let's say if I write a
statement here and if I try to print
something and if I make a spelling
mistake let's say if I make this as a
capital P of course your IDE gives you
an error here but even if you compile
this code you will get a compile time
error so it says either cannot find
symbol print now this type of errors are
actually easy to solve because your
compiler will show you hey you know you
make a you made a mistake here so this
is capital P this will not work so you
will know okay uh I have to make it
small and then it will work right of
course when you compile this code you
will not find any error now so when you
get error like this this is syntactical
errors and also a compile time error
which are very easy to solve the second
time of error we have is run time what
is run time without now in fact let's
talk about logical first and then we'll
come back to runtime now logical error
means everything is working there is no
compile time issue everything is working
and then you what you did is you added
two numbers let's say you added two plus
two and of course for this the output
you were expecting is for and the output
will be full and that's very simple
right but what if you did some
calculation not a simple code like this
you did a multi-line of code where the
output is not four output is five now it
is working there is no compile time
issue there is no runtime issues not
like at runtime it is getting stopped
but the output you are getting is wrong
right so you got five where you wanted
four now this type of others are called
logical errors also sometimes we call
them as bugs so even this type of
problems are actually difficult to solve
because you need to do a lot of testing
you know if you heard about this
whenever you make an application you
have to test your application as well so
in that case you will do testing you
will check for the inputs and outputs
and everything
so maybe you will able to solve this
problem but the thing is
from the developer side you do check
compile time issues which compiler will
help you there you do proper testing
where you can solve logical issues now
once everything is tested you can ship
your product to the client and client is
happy there is no compile time issue
there is no logical issues now runtime
issues are a bit different the problem
is in runtime issues what is what is
happening is everything is working I
mean compile time issue no problem your
code is working as well but suddenly
because of some reason the code just
stopped working you got errors okay uh
basically you know whenever you get
errors one time others your execution
normally stops and that's an issue let
me get an example here so let's say uh
you made an application where you your
application opens a file a txt file from
a C drive okay or maybe a home folder in
Unix system till this point it was
working because the file was there and
now let's say uh you deleted that file
so yesterday night you are doing
something some experiment with your
system and then the file is no more and
now today when you are trying to use the
application application is trying to
find the file the file is not there it
will give you a runtime error the
execution will stop in between now you
will say what's the big issue right you
can restart the application
yes you can and everything will work
provided the application is not that
critical if you are using a calculator
and calculator stops in between that's
okay you can reopen it when you're
playing a game and suddenly The Game
Stops
you can do it but let's say you are into
a game battle where where you will get
let's say one million dollars if you win
and suddenly your game crashes now we
don't want that right uh we can also go
for some applications which are the
critical example let's say if you talk
about medical softwares you have all
those scanning machines and then which
where you go inside the machine and then
it scans right it throws some place or
some things I'm not sure about medical
terms but what if the software just
stops in between risky what if you're in
a plane and then the plane software
stops working very critical right so you
have to make sure that even if you get
the errors runtime errors it should not
stop your application I'm not saying
they will not be a runtime error I'm
just saying we need to handle the
runtime errors so this runtime errors we
can call them as exceptions and
basically we need to handle the
exceptions okay so handling the
exception is very important and that's
what we are going to do in this set of
videos so in this video we have talked
about what is exceptions exceptions are
basically one time matters it's not like
we are going to stop the entire metals
of course we'll try to check for the
conditions you know if when you try to
open the file first you have to check is
the file exists if the file exists then
you open try to open the file those are
the things you can avoid runtime errors
let's say you're dividing a number by
zero so when you divide a number and if
you divide by zero it will give you
exceptions
so even before divide if you can check
if the denominator is non-zero then
divide so those are the checks we can do
but in case if there's exception you had
to you have to handle it now let's try
to handle the exceptions now we know
what is exception let's try to handle
them so what I will do here is first of
all let's create exceptions right that's
why then we'll then we'll know how to
handle the exception now even before we
talk about handling the exception what
type of statements we need to handle so
for that what I will do is let's talk
about statements since statements can be
of two types test statement can be of a
normal statement and a statement can be
a critical statement okay see in real
life as well we try to think about
situations which are normal and we try
to think about situations which are
critical example let's say if you're
walking with a kid on the street and or
let's say in the mall or in the
restaurant and then of course you will
grab the hand of kid right but what if a
kid just runs in that case if it's a
restaurant you will not be that Panic
right you will try try to say okay he's
roaming around and then you will try to
catch the kid but what if the same
situation happens on the street a busy
highway where you are holding the hand
of a kid but kids try to run in that
case you will jump to grab the kid
because that situation is critical in
the same way when you talk about
statements it can be normal statements
and critical statement example if I
write a simple statement here which is
int I is equal to 9. now this statement
is normal statement because we know what
what may go wrong here everything looks
good right so this is a normal statement
but what if you say ain't J is equal to
I divided by or maybe I can say 8
divided by I now this statement can be
critical if you look only this statement
now why this is critical is because if
the value of I is 9 that's completely
fine you will get the output example if
I just come back here and if I try to
print the value of J in fact you know
what I will do I will just make this 18
so that it will get some output instead
of 0. compile and one this works right
but what if the value of I is not 9 it's
0. now in this case first of all let me
just create the screen so that we can
see the output properly and you can see
we got an error it says exception
exception in thread main uh which is the
exception is this arithmetic exception
so if you can see it's arithmetic
exception and the message is divided by
zero now the moment it happens it
actually stops the execution let me show
you that if I try to print by here you
will see if I try to run this code
and run you can see it is not printing
by the result is not printing by is
because at this point the execution has
just stopped okay so that's why it is
always better to handle the exception
even if you know nothing may go wrong if
you think that's critical handle it how
that's a question to handle the
exception what you can do is you can put
this type of statements in some other
block now first of all let me just
declare the variable here by zero and
then
this is a statement which is critical
right so what I will do is I will just
put that in a separate block so I will
put that in a separate block some
something like this and now what I'm
saying is hey Java just try to execute
this code okay if it works that's fine
otherwise execute the other part don't
stop the execution the way you can do
that you can say hey Java try to execute
this statement so I can say try try to
execute okay Java will say okay uh now I
know that you are just trying to execute
if not it's not working then I will
continue with the normal execution here
but then what if Java tries to execute
this and there's a error in that case it
will throw the error and you as a
developer you have to catch the error so
in this case you will catch the
exception the moment it throws the
exception it is showing you an object
and you have to accept it as an object
so you will create an object or you will
refer that with an exception class so
this exception here is a class and you
are referring that with any object will
do it's not just a you can say obj as
well but most of the time you will say e
because it makes sense right exception e
you can say obj as well that perfectly
works but let me say e here and if you
want to print something you can do that
here so whatever handling stuff you want
to do you can do that in the catch block
so I will simply say something went
wrong okay so what I'm doing is I'm
trying to handle the exception if it
works that's great if it is not working
it will execute the catch block now
let's say the value of I is not zero the
value of I is let's say 4. in this case
you can see there's no exception so
let's try to execute the s with the
value 4
and if I run this code you can say it
says 4 and buy there's no problem with
the value we got 4 because of this
statement and we got by of course
but then what if something will go wrong
what if the value of I is 0. now in this
case this will throw the exception so it
will execute the catch block and I'm
expecting it should print something went
wrong let's try compile and run oh you
can see that it says something went
wrong now even if something goes wrong
the execution is still happening the
value of J is 0 because before the
execution of this try catch the value of
J was indeed 0. right that's how you
handle the exception and again you don't
have to put all the statements here you
can you can put normal statements in try
as well that completely works but it's
better to put only critical statements
inside my blog and you can write
multiple try blocks uh so one we have it
here what if we have some few more
statements here you can try catch that
as well that that works so I hope you
got the idea what is tried try will
basically try to execute these
statements if everything goes good it
will execute the remaining statement if
something was wrong if there's exception
it will execute the cache block so Point
remember the cash block will be executed
only in case of exception otherwise cash
block will be skipped so that's it from
this where we talked about try catch and
we have seen how to handle the exception
okay so we know that to handle the
critical statement we have to use try
block and inside that if something goes
wrong it will execute the cash block
otherwise it will simply execute the
remaining statements okay that that
makes sense right now what I will do is
I will try to print the exception as
well so that's why you can actually
print the exception so we are saying
something went wrong let me just remove
one dot from here so that we can save
some space and after this I want to
print the exception as well I want to
see the message what it says
so to do that what I will do is I will
compile this code and run you can see it
says something went wrong okay that
because we are printing that apart from
it the message which you are printing
here which is e it says arithmetic
exception oh okay that means apart from
exception we also have arithmetic
exception cool that also makes sense
so just try to remember this point that
apart from exception there is one more
class here which is called arithmetic
exception we'll see that in some time
now what I will do is I will try to
create some more exceptions here one of
fit is this if I create an array let's
say the array is of type integer and
let's send nums and I will say the size
of this array is let's say five now in
this case when you have a size five of
course by default all the values are 0
of this nums and you can fetch the
values let's say at this point I'm
trying to print the value of nums of 0
or 1 let's say one of course it will be
zero because the values are zero and I
will also try to print the nums of five
now see when you say nums are 5 what
value you will get now first of all the
size of this array is 5
and then if you are saying you're trying
to fetch one that means you're fetching
basically second element because the
index number starts with zero so zero
one two three four oh so for the five
elements the index number ends at four
and we are trying to get the value from
five okay so basically we are going out
of bound okay so let's let's see what
happens if we do that uh first of all I
just want to make sure that I don't have
this exception 0 here or maybe let's
let's keep it zero I will say compile
and run of course we will get that error
because uh the dividing number which is
I is still zero let me just make it two
see the problem is the moment you get
exception here it will directly jump out
of this try block it will not even
execute the remaining price statements
okay and that's why we have not seen
those outputs now what I will do is I
will just try to compile this once again
and run
this time if you can see we got a
different exception yeah it says
something went wrong that actually makes
sense because it is executing the cash
block but look at the exception the
exception is add a index out of bounds
exception which means the size of your
array is limited and then you are trying
to access the element outside it and it
says that it says index 5 is out of
Bound for the length five okay uh makes
sense so basically apart from automatic
exception we have other index outer
bound exception as well but I have only
one issue the issue is why we are
printing something went wrong see you
know you try to show the message to the
user as well and if you can see the
actual the problem is with the user what
if the value of I is coming from the
user what if the value of this 5 here
numbers of 5 is also coming from the
user now user is not sure what is the
problem here it says something went
wrong you have to be very specific here
you have to say Hey you cannot divide
the number by zero so user will know
okay the values which I'm entering is
actually wrong I should not be entering
a denominator which is zero okay or
maybe you can say you know you're trying
to access the element outside the array
the user will know that you know you
have to be in your limit I want to print
a customized message here so if I print
here something like this if I say cannot
divide by zero that looks like a good
message okay let's not print this a e
anymore let's only print cannot divide
by zero and let's see what happens okay
clear and I will keep the same error the
other is still with the array not with
the denominator but if you run this code
you can see it says cannot divide by
zero no that's weird because I'm trying
to fetch the value which is outside the
limit and it says cannot divide by zero
that's wrong this is the error makes
sense when the value of I is 0 right so
if I compile this code and run now this
works you can say it says cannot divide
by zero but then if you if the value of
I is not 0 in that case as well it is
printing cannot divided by zero it's
because the moment you get the the
exception is in dry it can be from this
statement or this statement it will
execute the same cash block and in the
same cash block we have the same message
see what you can do is before printing
you can actually check if you can check
the type of this e you know is e
arithmetic or is e either index Auto
bound and then based on that you can
print a different message that's one way
or what you can do is you can ask your
Java itself hey Java I want you to
handle different exception so you can be
very specific you instead of saying
exception I can say it is arithmetic
exception now I'm being very specific
here I'm saying I'm not talking about
exception I'm talking about arithmetic
exception when arithmetic exception
arises print this message but what if
there is an array index out of bound
exception let's see if we are able to
handle that so if I compile this code
now okay first of all let me just make
this I as 0 and let's see what happens
again I will compile and run you can say
it says connector by zero that makes
sense because we are able to handle the
exception and you can see we are
printing buy as well that means we are
handling the exception
but if you make this as two and if you
try to compile this and run oh you can
see that we are not printing by this
exception you can see it's a there's a
cross symbol as well it says other index
autobound exception that means we are
not handling it even if you mention that
in the try block if you don't have a
catch block for it that means you're not
handling it how do we handle that so in
that case what you can do is you can
write multiple catch block so you can
write catch here and in this sketch you
can mention add a index out of bounds
exception that's right we have to create
one more catch Block in which you'll be
having a different type of exception
and here we can print stay
in your limit again I'm just trying to
be witty here but you can print a
appropriate message whatever you want to
uh now if you try to see what happens if
I compile this code once again
and one you can see it says stay in your
limit there's no abnormal exit of the
code it is executing everything and this
time it is executing the cache block the
second cache block not the first one but
what if you make this zero then
and again it goes in sequence okay so in
try block it goes in sequence it will
first execute this statement which may
throw arithmic exception and if that
works well it will go for this one this
might do an exception which is at the
index.bound exception so let's see if
that works compile and run you can see
it says cannot divider zero so you can
basically have two different exceptions
here now what if there is another type
of exception here which we are not sure
about you know there are a lot of
exception classes it's not like we only
have these two in fact in the next video
we'll try to understand some of the
famous classes or famous exception
classes we'll try to work on that but at
this point there are multiple exceptions
and we are handling only two you know
it's always a good idea to handle all
the exception but we are not sure what
exception it can arise so in that case
you know to be on the safer side at the
end you can handle something with
exception now exception handles
everything if you remember the concept
of in heightens where you have a parent
class child class so exception is a
parent class it can handle all the
exceptions okay now you can say
something went wrong because even you
are not sure what went wrong so you can
say something went wrong now if there's
some some exception which you are not
handling in that case if you execute
this part
to give an example let's say I create a
string here string Str and let's say the
value of Str is null as of now and body
fight will be null and then here what
you're doing is you're trying to get the
length of this string so what you can do
is you can print string SDR dot length
now if you try to find a length on a
null string it will give you a different
type of exception first of all I just
want to remove this exception I don't
want exception on line number 13 I just
want it to work so that it will execute
this line which will give you exception
and let's see what happens if you say
clear and compile and run it says
something went wrong now what went wrong
is because there's a new type of
exception in fact here it's a good time
to actually print e because it should
print something some exception so that
you'll understand I'll try to print this
and you can see it says something went
wrong because that's what we are doing
here
and then it prints the exception which
is null pointer exception now this is
one more exception like this we have a
lot of exceptions
and we'll understand that in the next
video but then before that we have one
more thing what should the sequence here
the sequence is whenever you have a
child and parent make sure that your
parent is at the bottom so you can say
exception is a top class right parent
let me show you how it looks like so if
I go to Ultimate exception now
arithmetic exceptions are class which
extends runtime exception so runtime
exceptions are present class for
arithmetic but if I click on runtime
exception you can see it extends
exception here so exception is a patent
of parent and in fact this exception
actually extends through able so there's
one more class called through able which
is like the topmost class and yeah so
that's how you basically the hierarchy
looks like in fact I will show that in
the next video as well but make sure
that you have at the end but if you try
to keep this on top here it will create
an issue because the exception can
handle everything right at this point if
you get the exception it will try to
search for a catch which can handle this
exception and it looks at Exception by
saying hey exception can handle
everything right then why we even need
this too and that's why it says you know
it says this exception cannot it's
unreachable cancel that message there it
is unreachable because everything is
handled by this exception so it's a
practice or it's compulsion to have the
parent class at the end now as we have
seen exception is a super class right
and in that we have a lot of subclasses
now let's try to understand the entire
hierarchy in fact we'll not talk about
all the classes let's try to give you
the general idea and with this idea
we'll understand okay what class belongs
where and which exceptions are
compensory to handle and which are not
okay that's important point to remember
so on top we have the object class now
why it's on top because every class in
Java extends object even if you don't
mention it's there right so give let's
give the respect to object class now
below that we have one class called
throwable now if you remember while
searching for the class uh we have seen
exception class extends variable so
that's on top one more trivia here most
of the names which ends with able are
actually interfaces okay runnables
realizable cloneable but coming to
exception tribal is also able at the end
but it's a class okay that's the only
exception which I have seen till now now
below this we have two and okay that
sounds weird because we have only some
exception right so we have exception
here and apart from this we have one
more which is called error okay now why
we have not talked about error yet we
are only talking about exception the
thing is when we talked about runtime
exception we have mentioned that it is
something you can handle okay so
exceptions are something which you can
and you should handle others you can't
okay when the others hit it will simply
stop the execution normally it doesn't
happen but if it happens you can't do
anything with that example of this it
can be the thread that what if your
threat dies example of this can be i o
error something goes wrong with the
input output we have few more which is
your virtual machine error it can be one
of the example I can give you here is
what if you have out of memory so what
if your memory is not there so what how
can you handle that okay so this type of
Errors you can't actually handle so this
is something it's there it will not
happen but we cannot handle that even if
it happens what you can handle is
exception now in exception as well we
have multiple options here so we have
the first one which is runtime exception
so we have the subclass of exception is
one-time exception and on the other hand
we have a lot of different exceptions
here example of this could be a skill
exception example of this could be IO
exception and many more but we are just
trying to understand the simple one so
we have these two uh we have many more
as I mentioned now in runtime exception
also we have lot of different exceptions
here we have seen most of it in fact we
have seen a arithmetic exception uh then
we have add a
index out of bounds exception and then
we have null Point exception now all
this comes on the runtime exception this
is an null Point exception now the thing
is why you have to remember this thing
not everything you have to remember but
few of them see all these runtime
exceptions are actually called unchecked
exceptions and all the other here on on
this side they are called checked
exception now why they are unchecked and
checked most of the time when you write
the line your compiler will not force
you to handle the exception okay it will
say hey it's your choice to handle the
exception so all the runtime exception
all this all the classes here it's your
choice if you want to handle them or not
but whenever your compiler sees that
there is a line which can raise a
exception which is not runtime exception
example it can raise uh SQL exception IO
exception in that case it will ask you
compulsory to handle the exception
if you remember when we were trying to
load the class with the help of class
dot for name on the right side of the
method we have mentioned it throws the
io exception right so it was forcing you
to handle it okay okay we have not
talked about those yet but we'll talk
about it so basically uh these are all
checked and this are all unchecked here
and there's something you should not be
worrying about it will not happen most
of the time and this is something you
have to handle by yourself so I hope
this diagram makes some sense this is
the top class which is there in every
Java code and this is the authorable
which is a parent class of exception and
error in exception we have lot of
different exceptions if you get SQL
exception in your code you have to
handle it compulsory I have exception
compulsion apart from this if you have a
runtime exception it's your choice to
enter it or not but as a good programmer
if you want to keep your client happy
please handle the exceptions now let's
try to to understand a keyword called
Throw okay so basically we have two
keywords here one is throw second is
throws we'll see them one by one so what
I will do here is first of all I will
just reduce the number of lines we have
so that it will be easy for us to
understand I will remove all the
exception okay I will stick to one which
is divided by zero and let's put only
one statement here let me also remove
this one because not needle we only want
to exception arithmetic and if something
goes wrong which we have not handling uh
that will be handled by exception
okay so let's say when you divide this
number of course the value of I is 2 so
everything is good and you know most of
the time people will put curly brackets
on the same line and it normally works
and this basically preferred okay so
let's say when you do this execution of
course there's no exception here because
we are dividing by two right so if I try
to compile this code and run everything
is smooth you you can see we are
dividing the number 18 by 2 which is
nine and that's what you got here
because we are printing the value of J
and then we are printing by everything
is normal now the thing is what if I'm
dividing this number by let's say 20.
now in this case when you have a greater
number of course you can divide 18 by
20. now the question here would be zero
if you can see the value is 0 and
there's no exception but what if you
want to create or you want to generate
an exception maybe you are doing
something here let's do this thing let's
say the value of I is zero so of course
you will print cannot divide by zero now
instead of printing cannot divide by
zero what you can do is let's skip this
part let's say let's not print any error
let's handle the error if someone is
trying to divide a number by zero I want
to divide the number by 1 18 divided by
one okay so what I'm doing is I'm not
printing anything I'm just trying to
handle it it will print some output so
if I compile and run you can say it says
18 okay I don't want to print
added or something if someone enters a
denominator 0 I will say maybe I can
also print here that's the default
output so that if it prints 18 it will
also print that's the default output if
you can see if I do that so it will say
that's a default output it will print 18
okay now what I want is every time this
exception it should do this thing so
it's not just about printing the message
you can actually handle something
example let's say if you're trying to
connect to an internet and then the
network is not there of course it will
throw the exception so instead of
sending a message to the user we were
not able to connect to the server you
can simply retry right so what you're
doing is you're trying to handle the
exception here we just tried of course
this is not a good logic I'm just trying
to make you understand how we can do it
one more example let's say you have two
databases one is a primary database
second cell backup database you are
trying to connect to a primary database
and something goes wrong of course you
will not simply tell user hey you know
we are not able to connect to the
primary database you will simply try to
connect with the backup database and
that's what you can do in the catch
block that's what we are doing here with
this logic now let's say you are
dividing a number by 20. now in this
case it will print zero okay but what if
you don't want to print 0 you want to
print the default output is 18. maybe
you won't do that that means what I'm
saying is even if the catch block is not
getting called I want to call the catch
block because in the catch block you are
basically trying to handle the exception
and if you don't have the exception it
will not call the cash block that is not
something we want so to solve that
problem what you can do is you can
basically check if the value of J is 0
okay because we don't want zero in this
case if the value of J is 0 you can
basically call The Catch block but how
do you call the catch block catch is not
a simple function right where you can
write cats by passing a message node
it's not a normal function or normal
method what you have to do is you have
to basically use a keyword called Throw
and you have to create an object of
arithmetic exception so you can do that
you can simply say new
arithmetic exception it's a class right
you can create the object it's that
simple now what you're doing is you're
basically trying to create an error here
you're trying to throw the error so this
is the exception you got you got the
object and you are throwing now since
you are throwing catch will catch it
okay let's see if this works compile no
issue Run Okay so that it says that's
the default output it is printing 18. so
you got zero here but then we are
checking if it is 0 then throw the
exception
okay uh maybe you want to connect to
another database which you have written
the code in the catch block so you can
do that here okay you can literally call
The Catch block with the help of throw
keyword there's one more thing what if
you also want to print the message
somewhere here you want to print e Now
by default if you try to compile this
code and run yes it will say a rhythmic
exception but you can see it is not
printing the message I want the message
as well remember it was printing slash
by zero or divided by zero I want to
print such messages so you can actually
pass a message in the Constructor you
can say I don't want to print zero okay
something like that whatever your
message you want to send you can do that
in the Constructor so you can say it
says this is your message I don't want
to print zero so if you want to send a
message put that in a Constructor it
will do it for you don't worry you don't
have to manually go and type the message
so whatever message you have every time
you create this object you can pass the
message and that's how we can use a
through keyword so so just reiterate row
keyword is used to throw the exception
okay and then catch block will be
catching it now basically we were able
to throw the
throw that which is arithmetic now
to the exception and what if you want to
throw your own exception let's say I
don't want to throw ultimately exception
I want to throw my own exception can we
do that can I say my exception you can
see uh straightforward it says my
exception cannot be resolved that's why
we don't have any class called my
exception but I want my own exception
here or maybe I can say issue of my
exception I can say Naveen exception you
know what Naveen actually means new okay
so it's a it's a term which means new
okay anyway so I want to have a new
exception here the way you can do that
is by creating a class which is called
Nomine exception and done oh okay we
have to also create a Constructor
because we are sending a message so what
I will do is I will create public now in
exception which accepts a string Str
okay string string that works for me
and still is not working it says no
exception of type novel exception oh I
have created a class right the class is
there what's the problem I have created
my own exception and it's not accepting
it see the thing is you can't simply
create a class and call it as exception
see exception needs special features
right and we all know if you want to get
something you have two choice you can
actually build something or you can just
get it from your parents so I can simply
say extends exception so what we are
doing is we are getting all the features
from the exception okay so you can say
now in exception extern exception and
now it is not crying okay now the only
thing is if you try to compile this code
okay not this one compile first and run
it says something went wrong oh that's
weird why something went wrong I want
actually to print oh okay the thing is
you are doing an exception but you are
not catching of an exception I want to
print this one that's a default output
so what you can do is in shop knowing
automatic exception you can say nothing
exception here and you can accept the
object and then you can print this
message that's the default output and
also you want to print e to get the
message the message is this I want to
print something now if I try to compile
this code again and run oh it works can
you see that it says that's the default
output and the error is Naveen exception
okay that's good where is this message I
don't want to plane zero the thing is
the message which you have sent actually
is received here but this output when
you're trying to print a here is
actually handled by the exception class
okay this should know that you are
accepting a string so what you can do is
if you go to exception even exception
has a Constructor which takes a string
and we all know how to call a superclass
Constructor we have seen that right so I
can simply say super and pass this
message so whatever message you are
accepting here just pass the message to
the exception and they will take care of
it you don't trust me let me show you
you can see that it says Naveen
exception and it prints the message as
well the message is I don't want to
print zero so that's how it works you
can create your own exception so just
reiterate now in exception is not a part
of java I'm creating my own exception
and yes you can do that the only thing
is you have to create a class with the
exception and this class need to extend
exception or runtime exception your
choice let's try with one-time exception
and if I clear this
compile run it works so you can extend
exception or runtime exception and the
only thing you have to do is if you're
accepting a message you have to pass the
message to the runtime exception
Constructor and that's how it works now
in this video let's talk about throws
keyword so we have talked about throw
keyword now it's time for throws now
this is not a plural form of throw it's
not like if you want to throw multiple
exceptions you will be using close a lot
of people have this confusion those has
a different working so before you
understand those what I will do is let's
talk about a scenario let's say you are
writing a method so let's say the method
name is D now of course in this method
you will write certain statements right
and it is possible that all the
statements there is one statement here
which is critical so let's say this
statement is critical and we know
whenever you have a critical statement
it is always better to write try catch
so let's say we have a try here for this
and we have a cache block as well so
just try to imagine this in a coding
perspective say we have a statement
which is critical and then you try to
handle that with help of try catch and
we're doing that in a method D okay and
let's say we have one more method here
which is called E and in this method as
well you are writing some statement out
of which there is one statement here
let's say the first statement itself
which you need to put that in try catch
okay because this statement is critical
okay so if You observe we have two
methods here which is d and e both have
a statement which is critical now of
course it makes sense to write try catch
in each of the method or we have one
more Choice here what you can do is
let's say we have a method which is C
and C method is calling d and e both
okay so C method is calling the method
and E method of course in C let's say we
have some more statements let's say we
have method C and then this you have
multiple statement out of which the two
statements are calling D and E of course
you can call methods right and then we
have some more statements here now if
you try to observe the situation what we
are doing is we are trying to handle try
cats by ourselves right in the D and E
but what if you could say hey you know
what d and e both have the same
exception so both have a critical
statement they will rise the same
exception so instead of handling those
exception inside try catch in each of
the method can we just handle the try
catch and see itself so what you can do
is you can put try here and catch so
when you are basically calling those
methods D and E you can put them in try
catch because both of the methods has a
critical statement in fact the entire
method becomes a critical methods right
because when you're calling it
so instead of handling those things here
let's not handle uh using try catch here
yes we have a critical statement but
will not handle the exception in D and E
you can handle the exception in C okay
but then even if you work with this it
will give you an issue it will say okay
there's a problem with d and e but still
it will stop the execution so one thing
you can do is you can write here throws
so you can say throws exception and same
goes here you can say throws exception
okay so by doing this what you're doing
is you're saying hey whatever problem
arises in D and E they will not handle
it they will just send the exception to
the method who is calling it sometimes
just call ducking the exception because
we are ducking it we are not handling it
the method which is we are into let's
say d and e says it's not my
responsibility so the method which is
calling d and e which is C in this case
will be handling those exceptions okay
and in C of course you have to have try
catch if you don't have a try catch in
see it will again create a problem for
you because it will stop the execution
now we have one more thing what if you
are not doing try catch here so of
course some method will be calling C
right so let's say B is calling C method
okay now in this case what you can do is
you can put try catch here and let's say
uh if you don't want to do try catch
here we have a main method now let's say
main is calling B method here even main
can have a try catch so basically you
can go up the ladder and you can write
try catch in whatever method you want to
write so if you write try catch in main
then B says okay even I will throw the
exception c will say even I will show
the exception I will not handle example
by myself c will say I want B to handle
it B will say I want main to handle it
and of course your D and E both says c
will handle it okay now that is called
ducking the exception for a particular
method but it is done with the help of
those keyword now this makes sense for
checked exceptions okay see for uncheck
exceptions it's not compulsion for you
to handle the exception but when you you
have a checked exception example if you
talk about IO exception okay now in
terms of IO exception which happens when
you use input output let's say you are
reading something from the file or
you're writing something something to
the file or when you're doing SQL which
is database connectivity at that point
as well when you're finding a query it
might raise an exception in that case
you will be getting a checked exception
and we know we have talked about this in
checked exception if you write that
statement it reads compulsory example
remember we have worked with one of the
thing which is called class dot for name
and in which you can mention the class
name let's say my class name here is
demo itself
so basically what you're doing is you're
writing this statement and this
statement says it might throw or it will
throw a class not found exception now
class not found exception is also comes
into hierarchy where this is a checked
exception so it is asking you to
compulsarily handle this exception so
you can put that in a try catch so you
can put that here and you can say catch
now which exception we have to handle uh
the name of the exception is class not
found exception and you can print not
able to find the class in fact let's say
let's write a class called calcare and
you know we don't have a calc class
nowhere okay now if you try to run this
code compile and run you can see it will
say not able to find the class now which
class we're talking about class is not
there in fact I can also print the error
message here with this so compile and
run you can see it says class not one
exception which class calc it's not
there but if you do it for demo all
there is no issue because we do have a
demo class here right so if I compile
this and run you can see it works it
says the default output blah blah blah
but there's no exception there's no
problem with this okay so in fact we can
also put this we can just cut this part
and let's say we are doing that in a
separate method so let's say we have a
class A and in this class A we have a
method which is public void show and in
this show we are doing this we are
trying to load the class demo here and
of course we have to call this now what
I will do is I will just try to remove
everything else so that we can make our
code simple and remove this custom
exception as well and you can see we
have a very simple code now and if you
want to work with so of course you have
to get object of a you will say a obj
and then you will say obj dot show okay
and now if you try to work with this
when you say compile and run you can see
there is no problem because anyway we
are not printing anything we are just
trying to load the class of course if
you write a static block here that will
surely work let's try to do that as well
because we have seen this let's create a
static block and I will print last
loaded in fact another the weird thing
is anyway we are writing main method
right so the class will be loaded anyway
but still we're just trying to see if
we're getting some output again the
class voltage is not happening because
of the load it's only because the main
method is there in the demo so anyway it
will be called but the idea is we are
trying to print something but what if I
try to work with a class called calc now
in this case if you try to work with
calc it will give you an exception you
can see it says not able to find the
class which is scalp okay cool and now
what if I don't write try catch so what
I'm doing is I'm saying hey I will not
handle the exception so in this case you
can simply go back to shows and say
throws class not found exception and you
can say there's no problem now because
this state treatment knows that show is
basically throwing the exception so show
says I'm not responsible to handle the
exception you know when you work for the
company there are some employees they
don't take responsibility of what went
wrong they will simply say hey talk to
my manager right so the same thing is
happening here it says hey I'm not
responsible to handle the exception talk
to my manager which is mean because many
is calling show so it is made
responsibility to handle the exception
and that's why you can see we got an
error here it says unhandled exception
okay so now you have two Choice what you
can do is either you can write try catch
here or you can say those last not found
exception okay so you have this choice
this is not recommended okay never do
that with main because if you see when
you're throwing the exception for main
the problem is who is calling main it's
jvm now you are asking jvm hey jvm you
have to handle this not a good idea
because JV will say okay if you throw it
to me I will simply stop the execution
so it's not a good idea to throw
exception for main but yeah for other
classes let's say for sure because we
know who is calling show it's your main
that domain will be handling it so don't
write those here okay you can just use
try catch in fact you can ask your IDE
you can say Quick Fix uh surround with
try catch and done you don't have to do
anything here and this might be new
print a stack Trace basically what it
does is it prints the entire stack which
method is calling which method and you
can actually track the entire method
calls so that you know because of which
method the problem has been arised okay
so if I compile this code and run you
can see this is the entire stack so
basically your main is calling show and
behind the scene we are calling class
dot fortnite which is behind the scene
is calling this and that so there's a
hierarchy of method which is getting
called that's what the print stack Trace
does so it's helpful to debug the
application but it's also good if you
want to print a message okay so yeah
that's about ducking the exceptions and
using this Rose keyword in fact we are
going to use this a lot in the upcoming
sessions so you will get used to it now
it's a good time to talk about how to
take input from the user I know you have
been waiting for this one a long time
because we have talked about different
concepts and maybe you had this question
in your mind okay everything looks good
we talked about objects classes and
heightens polymorphism but how do I take
the input from the user because in
between as well I've mentioned that what
if this value comes from the user and at
the same point you might be thinking how
Okay so let's try to answer that in this
video so basically if you want to print
something on the console so this is a
console right on the right hand side
whatever you have here it's a console
and if you want to print something on
the console what you do is you say
system dot out dot println right now you
have to understand this first see print
Ln is a method now if I ask you just to
think about it print Ln method belongs
to which class or it's a method of which
class now this is the interview question
a lot of people say that it is a class
it's it's a method of system class but
that's not the case see if I press my
control button on windows and command on
Mac and if I click on this if I hover on
this print Ln if I click on it you can
see it gives you definition it says
print Ln and print Ln method belongs to
print Stream So plainstream is a class
and println is a method of print stream
okay that means if you want to call
Print Ln you first have to create object
of a print stream but okay don't worry
you don't have to create the object the
beauty is the object is actually already
created can you see that it we already
have a out object and that's why we are
using this object for a long time so out
is the object of print stream but this
object is created as a static variable
inside the system class okay it's a it's
inside system class now since it is
static so we can use out with the help
of system dot out and once you have the
access to the out object you can call
println and that's what we have here
system.out.println so if I want to print
something if I want to print let's say
hello of course I can do that and I can
just compile this code and run it
perfectly works
now let's say I want to take the entry
from the user I have to say hey enter a
number now in this case when a user
enters the number how will I accept it
that that's tricky right so what do you
think what could be a solution here what
is the method we have to use now by any
chance if you're coming from CC plus
plus we use C out C in in C plus plus we
use printf scanf in C right and it's
straightforward right there are
straightforward methods but in terms of
java when you say system.out.printl and
it prints right it is out and that's why
it says out it is outputting so to input
there should be in right let's see do we
have in so if I go to system and if I
scroll down to out yes there is out here
and need to find in this is also in if
you can see in is a static method and
this object in is of type input stream
oh we do have it okay so if I go back
here and if I try to use system dot in
dot oh there should be a method right
because to print we have a print method
for the input there should be read oh
there's read okay great it works you can
see we have a read method and read
method returns uh into value right it
Returns the end value that's great the
only thing is it might throw an
exception and if you can see which
exception is IO exception and we know
what is IO exception now so you have a
choice you can handle the exception and
this is checked exception which means
you have to handle it it's your job to
handle it compiler will force you to do
that
so you can either use try catch here or
you can be evil and you can say throws
exceptions not a good idea but it works
for this code since we are learning so
we can do that but when you are making
an application don't do that try to use
try catch here okay so system.in.read
will give you the integer value that's
great what I will do is I will just put
that in a variable called num because it
returns a value right read will give you
the value so you have to put that in a
variable and once you have the variable
you can perform any operation if you
want or you can print it that's your
choice let's go back here and compile no
problem
if you try to read oh it says entire
number I'm excited let's enter 5 and
enter oh we got five but we also got
three now that's weird I don't want
three there okay let's try another
number let's see with three oh we got
fifty one what is happening here the
thing is this system dot in dot read
actually gives you the ASCII value for
the number you enter example let's say
if I run this code once again and if I
enter capital A it prints 65. so every
character on your keyboard has a ASCII
value the same way for a Capital Area 65
for small age is 97 I guess for 0 which
is 48 example if I enter the value of 0
it is 48 for Value 1 it is 49 so this
goes on right so basically it is not
giving you the exact value it is giving
you the asciate representation of that
value
okay that is tricky actually so what one
solution you have is what if you
subtract the number by 48 or maybe it's
not not 48 your subtract the number by
48 not by 48 minus num it is none minus
48 and now if you try to earn this call
you have to first compile this code
compile and run let's enter number five
oh it works now can you see that because
now we don't want to ASCII value we want
whatever ask about you are getting by
subtracting it right so if I enter six
okay if I enter 6 it works okay now it
works so we were able to manage it right
this is not an ideal way of taking the
input but that's what Java provides you
Java says we will give you this method
read which will give you ASCII value
what if you want to get a bigger number
what if you want to get example if I
give a bigger number here let's say 55
you can see it only gives you 5 because
it reads only one character at a time oh
that means if you want to read multiple
characters we have to use a loop but
let's not do that let's not take
headache off by ourselves so Java says
don't worry I will give you a
specialized class to work with this so
instead of using system.in dot read we
have a special option which is there's a
concept called buffered reader now
buffer reader is basically a class which
works with IO okay and it belongs to a
package java.io so if you want to use
buffer data you need to import this
package so IO exception buffer data
board belongs to IO package now whatever
class we have used to allow most of them
belong to java.lang which is Auto Import
but if you want to use any class which
is not there you have to explicitly
mention the package name okay so let's
create object or buffer data so we'll
say buffer data BF is equal to new
buffered reader
okay but what next
the thing is if you want to read we have
to actually pass the in object can you
see that if I go to Constructor buffer
leader buffer data Constructor says okay
I will work but first you have to pass
an object of a reader okay now which
date is talking about so basically there
is one more class which you have to work
with I know this code will be bit
lengthy because that's how Java is
implemented it but let's use it in fact
there is a better way as well which
we'll see in the next topic so we have
to pass the input stream reader so we
have to get object of input stream
reader let's say in in this case and I
will say new input stream reader okay
and whatever object you are creating
here just pass it here your job is done
but there's a problem you can see it
input stream reader also needs an object
of input stream okay in this case what
you can do is it needs object of input
stream right and if you remember when we
talked about in object it is input
stream object so what you can do here is
you can pass system dot in I know it is
bit complex and that's why in later
version of java they have introduced
better solution but I just want to show
you this option as well which was there
and people were using it for a long time
okay so you have to say input stream
reader in and then we have to get the
object of input stream reader then you
can create object of buffer data by
passing the object of input stream now
once you have it you can create a num
variable and you can use buffered reader
to read a line so you can see we have a
read line the only thing is read line
will give you the string okay we don't
want string we want integer so to do
that we have to use a special class
called integer dot pass int which we
have seen already and integer.pass int
not in okay so whatever string you're
getting basically you will get a number
in the string format you just have to
convert that into integer and now if I
try to print number it should work
otherwise we have wasted so much of time
compile and run let's enter 55 it works
doesn't matter how big your number is it
will accept it you can say we got the
number so basically this is how you take
the input from the user there's another
way which I will show you in some time
but the important thing is whenever you
use buffer leader it is trying to access
input stream reader and the beauty is
buffer data can take the input from
anywhere not just from system keyboard
it can also take input from the file
from the network and you can mention
wherever you want to take the input from
you can mention it here you can mention
the file you can mention all those other
stuff now the thing is buffer reader
whenever you're using it it's actually a
resource now why it's a resource is
because let's say when you are trying to
read from a file of course file is a
resource right and when you open the
file it is your responsibility to close
it when you open the network it is your
responsibility to close it when you open
the database connection it is your
responsibility to close it how will you
close it so once your job is done at the
end you can just come back here and say
BF Dot close consider we have a closed
method so it is all always a good idea
to close the resources again it's not
compulsory it will not give you error
but a good practice is close the
resources okay otherwise you are making
resources you are licking the file
you're leaking data you are keeping the
resource busy and the thing is if you
are using a resource no one else can use
it okay so don't do that don't be a evil
person here so you close the resource
okay so this is how you take the input
and I know you are waiting for the
better way of doing this let me show you
a simple way so instead of using buffer
data we can use one more technique here
which is a scanner now scanner was
introduced later in Java so if you can
see if I go to scanner class scanner
class was introduced in 1.5 so people
before 1.5 were using buffer data I know
bad days but yeah we got scanner here we
can create object of scanner let's say
SC we can use any object name doesn't
matter and we can say scanner now
scanner takes the system dot in that's
constant because we have to mention from
where we are getting the input are you
getting the input from the Soul are you
getting the input from the file you have
to mention that here and once you get
this scanner object the beauty is in
scanner you can say SC Dot and there are
so many methods you can see that we got
next line which will give you string you
can say next int oh that means it
automatically gives you integer value
you can also say next chart uh it will
it has so many methods but we are going
to use next int not next line because if
we use next line you have to pass that
into integer so let's use next tint
which will not create a lot of headache
for us and run enter a number 567 and we
got it so I know scanner looks much
better than buffer leader but yeah it
was introduced later so people before
that were using buffer data so we have
seen it in fact in the next video we'll
try to understand more about how do you
close the sources okay and that's why we
are teaching this concept now because
now we know what is IO exception and all
those stuff so yeah you have two choice
of taking the input from the user you
can use buffer Twitter or you can use a
scanner class okay now in this video
let's try to implement try with finally
our private resources basically so what
I will do is I will just remove
everything else of course we'll do this
once again we'll try to use buffer data
because we love it right okay we are not
doing an exception as of now uh we are
not running any code for that let me
remove that as well and here what I'm
going to do is let's try to understand
try now if we talk about try of course
in this try you can do whatever you want
normally we put the critical statements
right and then if there's a critical
statement which is throwing an exception
what you execute is a catch block right
and we know how to write a cash block
the thing is is it compulsory to have a
try with catch there's no compulsion you
can write you can write try but you can
see if I don't mention catch it gives
you an error the thing is if you have a
try and if you don't want to mention the
catch you can basically write finally
here so yeah so try can be used with
finally if you don't want to write catch
if you don't have a scenario where you
want to handle the exception you can
write finally but then what's the use of
try when you're not catching it of
course right try is responsible to
handle the exception and when it it will
simply close the exception which will
catch will catch it and then it will
solve it or it will print something
finally what finally is doing see the
thing is even if you have a catch block
here let's let's work with catch block
and in this cache block I will say
exception e and then let me create a
scenario which is int I is equal to zero
I know you'll be thinking I'm just using
the same example just for Simplicity I
just want to keep this thing simple and
here I want to say J is equal to 18
divided by I I don't know why I'm using
18 every time it's just because we have
used it before now we know this will
throw an exception so it is our job to
print something here so I will say get
lost oh so it will say something went
wrong ignore that get lost so something
went wrong right okay so if you get the
exception it will call the catch block
right now sometimes you what happens you
know you want to print something you
want to do something which should be
executed irrespective if you get the
exception or not example let's say if I
want to print buy here in the try block
the thing is if you compile this code
and if you run this code you can see it
says something went wrong it is not
printing by you know why it's because in
the try block the moment you get the
exception here it will call the catch
block and that's what it's not printing
a buy it will actually jump out of the
try block right so one of the solution
you can have is you can just write this
in Cache block as well okay so that
irrespective if you get the exception or
not it will print by so you can say it
is printing Buy in the catch block but
if you don't have the exception it will
print by which is coming from the try
block okay so at least we are printing
buy now of course in the real project
you will not be printing by the in real
project you will do something there are
some set of statements which you want to
do is respect you if you get the
exception or not now instead of doing
those things here one of the amazing
thing we got is finally so what you can
do is you can write your statement
inside finally now finally has this
amazing feature which is irrespect you
if you got the exception or not it will
execute the final block so in case of
exception as well it will execute the
finally block let me show you that to
you compile and run it says buy no
problem even if I get the exception
compile and run it says buy so finally
block now this block will be executed
irrespective of the exception okay and
the beauty is you can actually skip the
cash block if you just want to use try
and finally but why you will do that why
in this world you will write try with
finally you're not handling the
exception right see finally makes sense
whenever you want to close the resource
that's right whenever you want to close
the resource that's where you will be
using finally okay what I'm talking
about is let's say we are not doing this
we are using a variable called num and
the value for Num initially will be zero
and what I want is is I want to take the
input from the user and we know how to
do that right so basically we have to
get object of buffer data of course we
can use scanner here but let's use
buffer data so buffer reader
b r equal to new buffered reader and we
know if you want to work with buffer
data first you have to get object of
input stream reader we'll say
in is equal to new input stream reader
which will take the object of system Dot
in right and here you can basically pass
this in which you have created here okay
and using this buffer data basically we
can say okay we can num is equal to b r
dot read line and then we have to pass
it right we have to say integer dot pass
int okay now it says it might show the
error right but then you will say hey we
are handling right no actually we are
not handling we don't have a catch block
here right so basically we are not
handling the exception and that's what
it says so what we have to do is we have
to either handle the exception or we can
Quick Fix and throws okay this time it
is throwing two exceptions number format
exception and IO exception because we
are passing it okay that's fine with us
okay and let's say I'm printing the num
value as well now after doing all those
things we know one thing right whenever
you open the resource example is a
resource right it's always better to
close the resource now my question to
you is where should I close the resource
should I close the resource in try block
if I am handling the exceptional do that
in the catch block of course we have
tried two statements right instead of
that the finally block is normally used
to close resource so whenever you want
to close the connection whenever you
want to close the resource always use
finary block it is meant for closing the
resources okay the only thing is can you
see that we are creating the reference
inside the try block the scope is
getting over itself here so what I can
do is I can declare it outside and I can
use it inside so when I declare outside
even the final block can use it and I
can make it null initially and now you
can see there's no problem so basically
we are closing the resource in the final
block so Point remember here is the
finally block is used to close the
resource it can be for file for the
input for for the connections network
connection database connection
everything finally will be used for
closing it makes sense right okay before
I go ahead I just want to do one more
thing don't you think we are passing in
here so can I instead of passing in can
I pass the entire state see ultimately
we need object right an object is
created by this line here so actually we
can do this so we don't need this line
so most of the time when you read
somewhere it will show this type of
statements and that's completely fine it
works okay now one more thing so try
with finally works you can close it here
but you know we can actually optimize
this mode in the data version of java
they have introduced A New Concept which
is try with resources where you don't
even have to mention finally block
that's good right but how will you do
that so what this says in the trial
itself create a round bracket and then
you create your declaration whatever
object you are creating create them
inside your try block I mean inside the
brackets and you have to declare that as
well but for reader so you will not
mention that here now so what I'm doing
is I'm creating the object in the the
dry itself now watch The Adventure of
this the advantage is once the try gets
over this resource will be closed
automatically it's because if you go to
buffer data buffered reader extends
reader and if I go to reader you can see
it says closable
and if I go to closable it is auto
closable so whenever you have a class or
the interface which is auto closable it
means that will be closed automatically
with the help of try you don't have to
do the closing manually so this is try
with resources so you have this syntax
option you can use Drive finally that
depends upon how you want to implement
this I prefer to use try with finally
because I know which resources I can I'm
closing and sometimes you have multiple
object created so it's good to use
finally but if you think you can make a
shortcut this also works so this here is
called try with resources in this video
we'll talk about threads now what are
threads now think about this when you
run the application of course the
software which you have written it will
be running on an OS right and below the
OS you have a layer which is called
Hardware so if you want to represent
this what we normally have is we have a
software which you built of course so
let's say this is your software and this
software basically runs on and Os of
course on this OS you'll be having
multiple softwares right and underlying
that is the hardware right so this is
where you have the physical set example
in this uh you will be having your CPU
you'll be having your RAM this is what
we use to run applications right
now if we talk about ram ram acts like a
temporary memory for your processing and
your CPU is basically something which
executes something okay so let's say in
in your software if even if you want to
add two numbers let's keep it very
simple let's say if you want to add two
numbers by saying two plus two now that
operation will go to OS and Os will say
okay you want to add two numbers let me
just send the request to the CPU of
course CPU will do the processing right
now CPU says okay that's a task I'll
just have to add two numbers it will do
some processing and then you got the
output
the thing is
for a simple operation it's so simple
right but then what if you are running a
big software let's say uh this is your
software and apart from this you have
multiple softwares which you want to run
on the same OS now of course in your in
your system you will be having multiple
uh softwares right and then sometimes
you want to run that at the same time so
that means OS should support multiple
software working at the same time so can
we say that that's multitasking
right so we have multiple tasks running
at the same time okay now most of the
modern os does support that the thing is
it's not like they are executing this at
the same time so this on the CPU there's
a concept of time sharing example let's
say this software one they software to
this software three uh let me just
remove this part for time media so let's
say if you have three softwares here
which is which you want to run on the OS
uh they will be going in time sharing so
your Osa OS can say hey uh the first
software you execute it will say Okay
second software now you execute and then
they will be executing badly by showing
the time okay
that's one thing so that's why we can
achieve multiple tasking and that's why
you know at the same time you can browse
a web page you can listen to a music you
can type a code so you can do all those
things at the same time because you have
a concept of multitasking but if you
talk about one single task okay what if
you want to break this break down this
task into multiple things
it is possible that in the same software
you have multiple
process or multiple things to run at the
same time let me give an example here
let's say you are writing something on
the editor so we are using vs code right
now the moment you write something on vs
code let's say if I say A B C uh you can
see the moment I type it it is showing
me that it is showing the text on the
software it is also showing us the error
right so that means these two things are
happening at the same time maybe uh we
can also enable some sound effects the
moment I type A to create a sound effect
so we are doing multiple thing at the
same time in the same software
so that means it's not just about
multitasking it's also about
dividing your task into small things the
smallest unit
how can we do that and that's where we
have a concept of threads so in the same
task in the same program you can have
multiple threads running at the same
time
okay so example when you play game you
know any game which you play Maybe Mario
or Cricket or football
I'm talking about video games okay now
at that point what happens you know if
you talk about Football let's say if you
have multiple players running at the
same time the ball is moving at the same
time uh the audience is cheating for at
the same time so you have multiple
things happening at the same time so
that is possible with the help of
multiple threads in fact if you see your
activity manager on Mac or if you go to
task match on Windows you can see
whatever task you have example I have a
Discord helper here uh we got login
window we got code helper so all this
software is another thing right stream
direct Zoom OS zoom zoom software
everything is running now all those are
tasks and individual tasks if you can
see we have threads there so the kernel
is consuming highest number of threads
524 then we got Java because we are
running Java behind the scene so Java is
using 20 or 20 42 threads
right so in a task as well you have the
smallest unit the beauty is they can run
parallely
and it they are lightweight basically
they don't they they also share the
resources it's not like if you have 42
threads they will consume 42 different
resources now they multiple threads can
share resources and that's why threads
are important to understand so in the
upcoming videos we'll focus more on
threads so I hope you got the just what
is threads and uh yeah just to redefine
that's a smallest unit which you can
work with and of course you can have one
multiple choice at the same time now
once we know why we need threads let's
try to create multiple threads here and
of course to create multiple threads
it's not like just because we have a
concept of threads we are going to use
in every application what if I say most
of the time you don't even create
threads by yourself see when you build
applications we use certain Frameworks
right now behind the scene this
Frameworks will create threads for you
so if you work on a big project there's
a high chance that you will not even
write threads by yourself but then it's
always better to get Hands-On on some
underlying Concepts right so let's do it
here so what I will do is let's say
let's go for a imaginary concept here
let's say I have a class hi whose job is
to print high okay or maybe I will just
say a Class A whose job is to print high
so what I will do is I will try to
create a function here public void show
and in this show I want to print hi
nothing fancy just hi here the only
thing is I want to print this High
multiple times so I will simply use a
loop here I can say int I equal to 1 and
I less than equal to 10
and I plus plus
okay and then we are putting this inside
a loop so of course when I call this
particular function which is show of
course it will execute height 10 times
right now let's say I I just copy this
code and I paste it here now what I'm
going to do is we have two classes with
this with the same concept almost
because they both have the same method
name which is show they are both are
running a loop for 10 times the only
thing is the second Loop actually prints
hello the first function here prints hi
the second one prints hello that's the
only difference and of course the class
name is different
and now I will go back to my main method
and here I want to create object of
these two classes so we got a class we
got B Class let's create object for them
so I will say a obj1 is equal to new a
so we got the object for a and then I
can say a object 2 is equal to new B and
we got the object for B okay simple
stuff and now I want to call those
methods of course I can simply say
obj.1.0 and
obituary what I'm doing is I got object
of both the classes and I'm calling the
show method and I'm thinking it should
work and why not it will white will not
work we have done so many Java codes to
allow it everything was working
let's see what happens so I will compile
this code and you can see there's no
problem there's no compile time issue
and if I run this code oh okay uh we got
the output right so we got all highs
here and we got all hellos right now
that's how your system basically works
you know your execution will start from
main main will say okay uh I mean when
your jvm is executing the Java code it
will start the execution from Main and
from when it says okay this is the first
line which I want to execute the first
line is simply create the object now
behind the scene in the Heap memory you
will get this object okay now the second
line says okay create the B object it
will say Okay B object done and since
everything goes in sequence it will
complete this task this two tasks then
it will go for the next statement which
is calling the show method of a class
right so it will say okay and now I have
to actually move so if you try to
imagine a pointer here not the pointer
in different languages I'm saying just
saying the which statement is getting
executed okay where is your executor
here so the executor says okay my job is
to execute this show method right so the
executor will directly jump to this
method which is show
okay now it will start executing this
method but when you are executing this
method
there is a hold on demo right I mean the
main method is not continuing now so
main will continue for the next
statement only when the previous
statement is done executing so once you
complete this show method execution then
only it will go for the next show right
and that's what it will do so it will
execute this show here it will run this
Loop for 10 times and it will print high
10 times now once this show method is
done with his work it will go back to
the main method and it will continue for
the next method calling so that
everything basically goes in a sequence
right now what I want to achieve here is
I want to say Hey you know when obj one
dot show is getting executed at the same
time parallely I want to execute this
show as well
okay so if you want to execute two
things at the same time or two behave at
the same time
since methods are behaviors we can use
something called threads okay so we can
say Okay I want to execute this two
objects but then they are not normal
objects you can't execute normal objects
in multiple threads or you can't execute
normal object execution simultaneously
so you have to use multiple threads here
so how do you make your normal objects
as threads now that's tricky right
it's actually very simple
if you want to make these classes or
these objects as threads just extend
with a class called thread it's that
simple the moment you extend with
threads or with a third class now this
class is not a ordinary class
this is a thread okay the same thing you
can do for B so you can say thread and
exit exchange thread okay and then you
can come back here and our job is done
right now we don't have normal classes
we have threads oh is it so simple okay
let's see compile and run oh it's not
that simple you can see they are still
running in sequence they are not running
in parallel what I want to do is I want
these two methods to run parallel so
while it is printing High it should also
print hello on the side by side okay
it's not it's not working so what I am
imagining with my code is what should
happen is see uh there is a main method
right so main will continue its work
here so main will keep executing
everything now there will be a point
where main wants to execute the show
method but with two different threads so
I want a show method here and I want a
show method here of course this show
method the first one is of a the second
one is of B but then your our main When
Calls show it should be with the new
thread so I want this to be a new thread
I want this to be a new thread okay now
just by mentioning that this class is
thread it will not get new thread for
you basically we want two threads now
the way you do that is by not calling
show what you have to do is you have to
call a method called start because when
you are thinking that at this point I
want to start a new thread you know we
want to start a new thread here we want
to start a new thread here we can do
that with the help of a start method so
we have to call this method and that's
what we are doing here so you have to
say start for both the threads okay see
we are saying that those are the obj102
but there are threads now
now the only thing is
when you call start it should also say
start right
is so now think is behind the scene when
you go to start so you can see if I go
to start start is a method belongs to a
thread class
so of course you can do your work here
but the thing is it will create new
thread for you
but it will call not the start method
even if you call it it calls a run
method so this thing you have to
remember in every thread you need to
have a run method that's how it works so
when you say start here it's it's almost
like you know when you are when you want
when you want to participate in a race
right so we have multiple we have
multiple Lanes there right so we have
multiple Lanes multiple people are
waiting to start the game here and of
course you took a position to run but
then you will not run you will wait for
it right what you will wait for you will
wait for some volunteer here to say
start right the moment they they shoot a
gun or they say start you go right in
the same way the moment you say start
here it will execute this one method
okay that's the point you have to
remember
okay let's see if this works now uh we
have done everything what we could have
done to make it work and let's say it
works oh okay
still not working now what is happening
here
see the thing is what if I say they are
actually running parallel the only thing
is when we are saying that see we are
starting with this one right obj1 and
then we are assuming that obj1 will
execute one high and parallely the
second thread which is the B thread will
execute hello at the same time
but the moment you give some time
because the machine is so fast now the
moment I give I have given some time to
the eighth where to execute it is
executing the entire thing at the same
time
okay let me show you what I'm saying
what if I do this for 100.
okay
and let's see what changes so if I
compile this code and run if you can see
if I scroll up things are happening in
parallel
okay so you can see we got few highs
here and then we got few hellos and then
we got few highs we got few hellos
okay things are running in parallel so
these two methods are actually running
at the same time
yeah so what happens is behind the scene
there's a concept of scheduler okay so
in your OS we have a concept of
scheduler now scheduler will say okay if
you want to execute something you have
to come to me first now it doesn't
matter how many threads have you have in
your system of course in my machine I
have shown you that in the last video If
you go to activity monitor you can see
we have so many threads here we have
five 24 threads running and only for one
task in total we I got 2382 threads now
of course you can't execute all at the
same time right now the thing is
nowadays we have multi-core CPUs so you
have multiple cores there right uh and
the beauty is you can execute multiple
thread at the same time so you can
execute let's say if I have four cores I
can execute fourth at the same time if I
have eight core CPU which is OCTA code I
can execute eight threads but we have 2
380 94 threads now how will execute all
so of course you can't execute all at
the same time right so they go for the
time sharing so scheduler in between so
let's say this is your OS here okay so
there's a concept of scheduler which is
responsible to basically allow
or thread to execute let's say we have
multiple threads waiting to execute okay
so let's say we have eight threads here
and then we only have two cores
available so on your CPU basically you
have only two cores right so security
knows you can actually run only two
threads at the same time so what it does
is it basically allows let's say uh This
Thread and this thread to execute and
then after they they execute they will
allow This Thread and this thread to
execute right so it is schedule a job to
allow which thread to go to execute on
the OS okay uh and that's why
so when when your scheduler allows some
time for your threads to execute your
thread might be executing this number of
iteration at the same time okay and
that's what's what is happening here so
basically we are running multiple pledge
at the same time
so yeah that's how you create multiple
threads with the help of the authority
class okay now let's try to execute this
thing simultaneously so what I want is I
want to of course they are running at
the same time but what I want here is I
want to execute High and Hello one after
the other so example if you can see the
output here we are printing so many
highs and then we are going for the
hellos right how do we do that see the
thing is you cannot control your
scheduler you can only suggest your
scheduler to give the priority so yeah
we have a concept of threads priority as
well example we have two threads right
we have obj one object two and we have a
concept of threads priority so let's say
let's I just want to understand what is
the current priority of the thread so I
can say obj one dot this is a method
called get priority which will give you
the current priority of a thread okay
let's try to print this let's see let's
see what happens compile there is an
issue okay we forgot to put one loan
bracket and compile this code and
run you can see it is printing all this
thing and we got thread variety where
it's here so you can see we got five
okay so since we are uh starting the
threads after printing the variety you
can see that's why the we got the value
first but we got the priority as five
now what is this by ID what's the range
basically so the range of the priority
goes from 1 to 10. so one is the least
priority 10 is the highest priority or
maximum priority and five is default
priority which is normal okay so by
default every thread will be having a
normal priority so what you can do is
you can change the priority of a thread
uh maybe you want the second thread to
have a higher priority so you can say
obj dot set priority and you can mention
the value so of course you can mention
one which is the lowest or you can
mention 10 which is the highest or you
can use some constants so thread class
has some constants which we can use
example we have Max priority we got Min
priority we got numpy ID right so if you
want to specify maximum priority you can
do that with the help of this constant
otherwise you can also say let's say if
you want to set the priority nine so you
can say Max by T minus 1 that will be 9
right but then by doing this it's not
like you will get all hello first and
then it will be high so even if you see
we are Printing High and then it is
printing hello and it's still hi hello
hi hello it's it's working in uh
simultaneously
the only thing is when you are
specifying that this the priority for
this thread is the maximum you are
basically suggesting to your scheduler
hey you know this thread should get a
highest priority it's not like scheduler
will give you that variety scheduler is
see different schedule have different
algorithms to work with and if it feels
okay now we have multiple threads and
they are reaching to a point at the same
time scheduler can say okay now I will
say the priority or maybe a scheduler
will also see who will take the lowest
time so if there's a threat which will
take less time so it might go for that
one so again as I mentioned different
scheduler has a different algorithm to
work with using priority you can only
suggest what should be done okay that's
one
so we know now how to set the priority
and get the priority apart from that if
you still want to make this work one
thing we can do here is
after printing hi see what is happening
is as a scheduler will give you some
time to execute right so let's say
schedule says Hey thread a you can
execute for let's say one millisecond
and we were assuming that in one
millisecond it will print one high but
no my machine is so fast in in fact most
of the machines are so fast nowadays
right uh in that one millisecond it is
executing this number of highs how do I
control this so one thing we can do is
after printing every High let's ask our
thread to wait
okay so the way you can do that is by
using thread dot there's a method called
sleep
now in this clip you can basically
mention for how much time you want this
thread to sleep so you have to specify
that in milliseconds So when you say
sleep you are asking your thread to wait
wait for 10 milliseconds and then
continue okay so what we are basically
trying to do is once you print high at
this particular threader the A3 will go
into weight stage right waiting stage
and then the B thread will execute hello
and again once B thread done is work you
can just put a sleep there as well now
the only thing is this Sleep Method will
throw as a remember we talked about
checked exception so this Sleep Method
basically throws a interrupted
exception so what you have to do is we
have to put a try catch all we can set
those but let's put try catch here so
with this suggestion I can say surround
with try catch and our job is done
right and just to simplify this what I
can also do is I can put this in one
line so you can see we got try catch and
then just to reduce the number of lines
we have we I'm just writing that in one
line the catch block the same thing can
be done for the hello as well
and you can see we got the sleeper as
well so we got two threads and now I
hope it will work let's compile and
run okay see that we are getting high
hello in sequence uh if you start from
here you can say we got hi hello hi
hello and then go on but if you can see
this is where you got two two hello at
the same time now it is possible that
after doing this calculation after doing
this iteration of hi hello
two threads are going back to schedule
at the same time and schedule has given
the chance to hello first so it all
depends upon how you work with threads
how I mean not you you can only make
multiple so it's all depend upon your
schedule how to run this and that's why
when you play games sometime you know
you can see some of the characters are
not moving a sequence or not in sync
because the threads are not working
properly there
so as a programmer you can just optimize
it more okay you cannot control it one
thing I can do is if I want the hello to
come after that maybe I can just put a
a sleep here as well
maybe of
two milliseconds so after so I I just
want both both of them to start with a
gap in between of two milliseconds
so compile and run and if you can see
I hope there will not be any High hello
which got two time print you can see now
it's all once it's because there's a gap
in between hi and hello who is reaches
to the schedule at the same time so yeah
that's how you can optimize again as I
mentioned we are just trying to optimize
it there's no guarantee that you will
get this output every time oh we got it
cancel that we got two hellos here again
my idea was just to optimize it and it
depends upon your schedule how to work
with this or maybe I can just if I make
it five then we can control that so try
this out and let me know how it is for
you and your machine
so we have understood two methods uh two
things from this video one is the
priority so you can set the different
priority for the threads main priority
Max priority and normal priority and you
can set any number between one to ten
and by doing this you're only suggesting
to your scheduler to give the current
threat my example IIT if you set it that
way and then we have talked about sleep
now when you say sleep it actually goes
into a waiting stage again we'll talk
about uh what is that waiting stage or
block State bit later but uh yeah that's
a stage which follows there are multiple
way is to create a thread one thing we
have seen which is of thread by showing
a class by thread but we have more
options but why do we need more options
now think about this let's say this
class A want to extend some other class
let's say we have one more class here
um and the class name is z and this P
the it I want this to be a parent class
and a to be a child class
so I want to basically make this a as
thread as well as I want to make this as
a subclass of Z and we all know right
the multiple inheritance in Java is not
possible so how do we solve this problem
so this idea of extending Authority is
not actually a good idea so the other
option we have is okay let's go back the
other option we have is if you click on
this threader If You observe thread is a
class which implements Venable okay and
if you go to the enable you can see we
have the method called run now this is
important right if you remember in the
code which we have written we have went
with a class name we have went with a
method name called run right that
actually means
that if I implement or enable here
instead of using a thread even this
should work
right because it has another method
so what I will do now is instead of
extending with a thread I will simply
implement it with the help of an
interface called runnable okay so both
the side now I have a choice of
extending a class as well if you have
some other class because we can have a
class which is extending another class
or implementing an interface at the same
time
but the point is you can create thread
like this as well you are making this
class A as runnable okay now by doing
this what how can you work with this
don't mind you go down first of all let
me just remove this we don't need this
code in fact you know before I continue
I just want to make some more changes to
the code uh the first the first thing
I'm going to change instead of having uh
let's say 100 question let's go for five
iterations so that we can see the output
fast
and yeah that's the thing okay so the
start will not work you know why the
start will not work is because in the
vulnerable interface we don't have a
start method the start method before it
was coming from third class okay that's
weird so we can't use this right
see the idea is if you want to if you
have a runnable class example this a is
actually a runnable class right a class
which is implementing an enabled so in
that case if you want to work with start
you can't do that so in that case what
you can do is you can create a two
different threads you can say T1 this is
your first thread
and then you got the two this is your
second thread right so we got two
threads here and instead of saying obj
one dot start we have to say T1 dot
start because we know that start method
belongs to a thread
and to also right you can see now we are
able to call start now let's see if this
works I will just go back here
and compile
run
oh that's weird we have not got any
output
see a thing is yes we got two threads
yes we are saying start it it's actually
creating two threads behind the scene
but it's not doing anything because
these two threads have no idea about
this obj1 ob2 they have no idea about
these two classes
so in that case what we do is if you go
to threaded Constructor you can see
thread has multiple Constructor one of
the Constructor takes as an enable
object
that means
obj1 here is actually a runnable object
you know let me prove that so instead of
using the a can I use runnable and we
have seen that right we can create a
reference of the interface and object of
a class
even here we have to say
the reference of the interface and
object of a class okay so what we can
now do is in this particular Constructor
of thread we can pass obj1 and here we
can pass object 2. so we are passing the
runnable object in the thread class or
the thread Constructor now there's a
link right so when you say start it will
know that which run run which run to
call so this start will call the Run of
these two classes let's see if this
works
I will say clear
compile run oh it worked and see that we
got hi hello hi hello and it is working
so basically whatever you want to
a thread we have two choice you can
extend our thread class or you can
Implement a enable interface the only
thing is this enable interface will not
have the thread methods in that case you
need to create a separate thread object
and then we can use these features
okay now if you remember we have also
learned about Lambda expression right so
like let's reduce this code by
implementing Lambda expression okay and
let's do that step by step
now if I ask you one thing the entire
class A why we are getting this class we
are creating this class is because we
want to implement runnable right
okay that makes sense how about if I
remove this class so of course this
variable will not work example let's say
if I comment the entire section here
okay when this part
come in the entire section you can say
this will give you another so I want to
create an enable obj1 but I can't create
a because we don't have a so can I say
news enable
of course we can right we have seen how
do we uh create how do we use anonymous
class to create the object so imagine
this is anonymous class right now in
this Anonymous class we have to
implement the method which is that in
learnable now which method is there the
same method which we have here so can I
just copy this code from here and I can
say copy
and paste let me remove the entire
comment section so basically what we're
doing is we are instant we are trying to
instantiate our interface with with the
help of a Anonymous class here
and in this class which is which has a
method which is run and basically we can
we are basically implementing this
Venable here itself right
okay that works let me just try if this
works before we continue
so I will say compile and run it worked
and see that we got the output okay
that's great
okay what else we can do uh can we do it
for the second one as well yeah we can
right but before we go for that one can
I convert this into a Lambda expression
and we have seen that right Lambda
expression works whenever you have a
functional interface and runnable is
actually a functional interface which
means I can use Lambda here and in
Lambda this is optional
so I can remove this I can put a arrow
here and I can remove this bracket as
well
okay this looks cool and I can just put
that back here okay so as you can see I
have written everything in one line for
the try so that you know it will be over
in one line and now uh can you can we do
it for the second object as well of
course I can I can just copy this code
and the only thing we know we need to
change is
the hello part right so from high we
have to make this hello that's the only
change I have to make and I don't even
need these two classes now I can remove
them and see the number of lines we have
reduced and also if you know that this
class would be used only one so this
makes much more sense to use right uh
the anonymous class and we can convert
that into Lambda as well so this is the
uh the Lambda version of it cool and now
we can simply run this and this should
work
compile and run and it works and that's
the beauty about Lambda Express right
and you can reduce the number of lines
you have
and there's no extra classes see it will
be tricky to type the entire thing from
start to end because till this point
what we are doing is we are trying to
convert the anonymous class into Lambda
expression which is easy by typing the
Lambda in the first scope will be
difficult so just try it out multiple
times you might make mistakes with the
syntax But ultimately you will get used
to it
so those are the two options we have
creating with the help of extending with
a thread and by implementing the
interface runnable
in this video we'll talk about race
conditions now we have talked about
threads right and till this point
everything looks good because we now we
know that threads are important if you
want to execute multiple things at the
same time our threads will be useful now
sometimes we create two threads
sometimes we go for multiple threads
maybe eight threads ten threads it
depends upon your application and as I
mentioned before there are certain times
when you actually write threads by
yourself otherwise most of the time uh
your Frameworks will do it for you okay
let's say you create your own threads
okay and then we know that threads are
good on the other hand we have one more
concept right so let's let me just write
it down here so if we talk about a
concept like threads threads are
important we know right apart from this
we have one more concept which is called
mutation so if I say mutation here now
what do you mean by mutation mutation
simply means that you can change
something example if you talk about
variables so primitive types variables
or object type variables we can change
is them right example if you have ain't
I so let's say if I say ain't I is equal
to 5 and then later on I'm changing this
value of I I'm saying I plus plus maybe
after some time I'm assigning the value
for I to 6 I can change this value right
and it is actually useful to mutate a
value of and of course that's what we do
with digital processing right so when I
say you got data you want to process it
most of the time you might want to uh
change the value of your variable and
that makes sense right so that is
mutation but then if you remember when
we talked about strings uh we have
mentioned that strings are immutable
right so there are some Concepts which
which makes them immutable so which is
good mutation or immutability uh at this
point if you if you can change something
notation looks good right so yeah so
till this point mutation looks good but
then let's try to discuss something more
what about threads our threads are good
of course if you want to make things
faster threads are good but then what if
you mix both of this what if you are
doing mutation with multiple threads
will this work so what I'm saying is
what if you have two threads let's say
T1 and T2 and both are trying to work
with the same variable I so T1 changes
the value of I T2 changes the value of I
now it will create instability in your
code I mean think about this but what if
you just have one bank account and you
got two cards two debit cards of course
as a single person you cannot use two
cards at the same time but what if you
have given the other card mind you I'm
talking about the same account so we
have one bank account and we have two
cards what if you give one one of the
card to your friend and then you went to
two different ATM machines okay and now
you are trying to uh withdraw the money
so let's say you in your account you
have 10 000 rupees and both of you at
the same time at the same second you try
to withdraw the money
you try to withdraw let's say seven
thousand seven thousand so in total
you're trying to withdraw 14 000 rupees
the balance is only ten thousand rupees
so that's an issue right if you try to
do things simultaneously and we'll also
do that in the code as well just to see
what happens so threads and mutation
together is not a good idea okay and
that's why if you are working with
threads always try to make sure that you
work with data which are immutable or if
you think that there's a method which is
which can do some mutation
make it thread safe now what is the
concept of thread safe so thread safe
simply means so if I say thread save
thread safe simply means that only one
thread
can work with that at one point example
if you have a method let's say show
and the show method so there are two
methods we're going to call so T1 and T2
so only one of them can be able to get
into show at one time so if T1 is
executing a show T2 cannot execute so
okay that's the Restriction we can add
but how let's see that in the code here
so what I will do is first of all I will
remove these two threads or maybe we can
just use these two threads as they are
so you can see we got two threads here
the only thing is I want to make sure uh
the iteration is not for
five the iteration is there for let's
say 1000 and maybe I don't want to print
something I don't want to apply a Sleep
Method just keep it clean and let me
just clip this clean as well so you can
see we got two threads and both are
doing something but as of now you can
see we are not writing any code here the
for Loop is basically empty
so what we can basically do here is
first of all what I want to achieve just
a very simple thing let's say I have a
class here called counter and in this
counter basically I have a method which
is public wide increment okay so that's
the increment method we have and then
let's also create a variable so let's
say the variable is Count okay and by
default the value for count will be 0
because that's an instance variable and
then inside this increment I'm just
saying count plus plus okay
so basically what we have is we have a
class called counter and in this we have
a variable called count
and then every time someone calls
increment it will be doing count plus
plus and of course if I call increment
once the value of account will be one if
I call increment 10 times the value of
count will be 10 right but then what I
will do now is I'm going to call this
counter or this this increment with a
multiple times
so before we even use that let me create
the object of counter I will say counter
C is equal to new counter and then from
this two threads what we have we can
simply say C dot increment so basically
I am going to call increment
multiple times now you tell me how many
times you are going to call it so of
course I'm going to I'm saying that
increment in both the threads and each
thread is going to do this
incrementation increment for 1000
iterations right now when I say 1000
10 000 in total this increment will be
called for 2000 right
okay let me just Retreat we have two
threads each three is calling increment
thousand times so in total the increment
will be called 2 000 times right so if I
go back here
and after it starts I just want to print
the value of count let's see what the
what's the current value of count is
now you tell me what will be the current
value of count so if I compile and run
now when I run this code I want this to
be 2000 right let's say what happens oh
it's only one one six the weird thing is
every time we run this code you will get
a different output for this what's
happening
see what we are trying to do here is let
me just do that on my pad here see we've
got a main thread right this is your
main thread and on line number
uh 34 and 35 what we are doing is we are
creating two two new threads we got T1
and T2 now T1 jobs is to call increment
thousand times right and T2 job is to
call increment thousand times and
ultimately we want this count variable
to be around 2000 right
but the thing is the main is doing
nothing right Main in main we are saying
hey just print the value of count
now we were expecting that T1 and T2
will complete the work and then main
will print count but that's not the case
anyway these two we have two threads
right T1 T2 and they are running any
anyway now when these two threads are
running in any case
they are running right main is doing
nothing so main says okay my job is done
I have started these two threads and now
I will simply print the value of count
so in between the iterations maybe T1
has done some iterations T2 has done
some iterations main is printing count
anyway we have to ask main hey you know
don't print count here let them come
back so as main continues let them come
back let T1 and T2 complete their work
by doing 100 iterations when T1 comes
back and T2 comes back
after this just try to print the value
of count and I'm sure at that point the
count will be two thousand so what I can
do is uh how do I ask main to wait for
T1 T2 so one thing you can do is you can
say T1 dot join now join in a special
method which allows your main thread to
wait for the other two threads to come
back and join
okay so if at this point if you want to
wait for these two threads you can use
join there okay but the only thing is
join me through an exception so I can
simply say add those declaration you can
see we got close exception anyway we
have done with the join and now I think
it should be good we should be able to
see two thousand so if I compile and run
oh
okay we were expecting 2 000 but we got
okay now we got two thousand now we got
1746 and that's why you know threads are
sometimes be unpredictable because they
have a different behavior and
unfortunately they cannot control
directly uh so what is happening here
the example which we have taken before
uh which was about the bank account it
is possible then when we have two
threads so we got T1 and T2 they both
are executing the same method and in
this method what is happening so when I
say increment it is actually getting the
value of count if you see we are saying
count plus plus right it's actually two
steps first it will get the value of
count the current value of count and
then it will say Okay count is equal to
count plus one because that's how count
plus plus works right so there are two
steps get the value for count and
whatever new value you get just add it
with one and then assign it to count
back so let's say when T1 reaches to
count the value of count is zero right
so if I just say this is the count value
is 0 then 0 plus 1 is 1. so the new
count value is one again if we trade
this part so this will be one the value
of count is one right so T2 goes there
T2 says okay uh give me the value of
count it says one plus one is equal to
two now again T 1 goes back T1 says okay
new value is two I will say 2 plus 1 is
equal to three and that's how the
iteration should go right but what if
both the threads reaches to this count
at the same time so let's say T1 and T2
both are reaching to do count at the
same time they both got the value which
is three they both said okay three plus
one is equal to 4. we got two iterations
I mean we called increment two times but
the incremented happens only once
okay that's what happens when you have
two threads working with the same
variable or shared variable
oh okay so mutation and threads are not
good and every time you run this you
will get different output now how do you
make this consistent okay you might be
thinking why we got two thousand years
because maybe your threads are not going
to the increment at the same time okay
so that's not the case in fact if you go
with a bigger number if I go with ten
thousand and ten thousand you can see it
will lose lot of different uh bits in
between
compile and run you can see 7000 we are
losing 7000 values we got nine eight
thousand values lost
right and the chances of getting 20 000
is way less now
so the point is this is not a good way
now how do you make sure that only one
thread works with that at one time
that's why you can do it right so
example event T1 is working with
increment T2 cannot work with increment
okay so T2 has to wait
in that case you can use a very simple
keyword you can use a keyword called
Synchro nice
you just use this one keyword your jaw
will make sure that this increment will
be called only by one method at a time
so if T1 is working with increment T2
has to wait
so if I compile this code now
and run you can see we got 20 000. now
it doesn't matter how many times we run
this you will get 20 000 because now
both the threads are not going to the
diet method at the same time
that's how we used two threads with the
shared variables and you make them as
synchronized so basically we saved
ourselves from this condition now in
this video we will talk about different
diff of a threader now if you remember
we have started with creating a thread
then we uh talked about the thread is
running and then we have talked about
Sleep Method we have talked about joint
method so basically we were basically
playing with the thread States right
where the thread was running and then we
asked this way to wage come back right
so how do we what are different states
available try to understand that see
every time you create a new thread that
goes into a new state okay so this is
your new state now apart from this new
state we also have something called a
runnable state okay so we have uh the
naval state
now after that we also have a running
State then we have a waiting state
or we can say also say block state
and then the last date is we have is
dead okay so we have
all the states available for the thread
now when you say new state what exactly
happens so when you create a new third
example in the code if you remember when
we said uh thread T1 equal to new thread
at that point it becomes into a new uh
the new state
now the moment you say start you know we
have this method we just start so when
you say start it goes to an enabled
state so maybe we can say start so when
you say start it says it goes into an
enable state
now there's a difference between
vulnerable state and running
the difference is when your thread is
actually running on the CPU that is
running state but when your thread is
executing and then uh it is waiting for
the scheduler that is into an enable
state so example when your thread is
running with the help of run method that
is your running State now what if while
you are running this and then maybe you
want to keep it on hold with the help of
Sleep Method
so that goes into waiting State now
apart from sleep we also have a method
like weight which can make it go into
wedding state right so when your thread
is running State you can also say wait
now wait will take it to the waiting
state right now how will you come back
now you will come back with the help of
notify the only thing is when you say
notify you will not come back to running
State you will go into the enable State
now whenever the scheduler is assigning
with the task or whenever scheduler says
it's your turn at that point it will go
into running State uh in fact if you if
your 30 is running and if you want to
keep it there you can also say stop
there's also stop is available but that
is deprecated actually don't don't stop
threads okay it will create instability
in your software but yeah once the work
is over it will automatically going to
stop State uh you can also send a thread
from the runnable to dead even with the
help of stop
even you can do that uh what else we
have here
okay so basically if we have this option
so whenever you create a thread that is
good that goes into a new state and then
when you say start it goes into enable
now depend upon your availability of
your CPU that goes into running State
now while running it will execute
certain things and then if at that point
if you want to say wait you can do that
with the help of sleep or you can do
that with the help of weight now the
only thing is when you say wait you have
to use a notify method to come back the
only thing is when you say notify it
will not come back to running status it
will go to the learnable state right so
it goes from the waiting to learnable
from running to waiting waiting to
enable that's the cycle it follows and
then again from runnable to a running
State yeah those are the states
available we have this number of states
in Threads especially in Java now let's
talk about collection the funny thing is
in this topic we have three different
types of collection it starts with small
say which is a collection API so let me
just write down somewhere uh so we have
a concept called The Connection API then
we have a collection
and we have collections now this is the
only thing I think it's confusing in
this topic now when I talk about
collection API I'm talking about a
concept when we talk about collection
I'm talking about an interface and when
you talk about these collections with s
it is your class okay uh so if I say hey
something belongs to collection API that
means it belongs to this concept if I
say collection I'm talking about the
interfaces and then there are some
classes which implement this and then
we'll talk about collections which is a
class and it has multiple methods to
work with
okay now why I'm talking about
collection here so the thing is whenever
you want to group The Elements right
let's say if you have one value you can
store that in one variable right I can
simply say int uh num is equal to five
and I'm happy right the only thing is
what if you want to have multiple values
now that's what problem creates how do
you store multiple values and I know you
know the answer right the answer is
array and we have worked with it right
so I can simply create a nums here
which is an array and I can say new int
and bracket I can mention the size which
is five now this is your added right and
it perfectly works okay then why we are
talking about this discoloration topic
see the thing is if we talk about
working with data if you talk about
working with algorithms
there is a concept called data
structures right and I hope you have
heard about that in multiple places why
data structures are very important the
way you fetch data the way you the way
you store data is very very important
now sometimes example let's say if you
store data in a box here now sometimes
you want to save data and you want to
fetch the last element okay so whatever
element has been inserted last you want
to maybe you want to fetch that or maybe
uh you you have another type of data
where you want to insert data in this
values and the value you want to fetch
is the first value right so this is
where I'm talking about the last in
first out and this is what I'm talking
about first in first out just take a
normal queue right example if you want
to take a ticket you go you stand in a
queue right in the same way this concept
which I'm talking about here is Q uh the
concept which I'm talking about here is
stack right now apart from this there
are multiple data structures which one
to work with right and we can actually
Implement all these data structures with
the help of array as well there's no
harm in that so as a programmer you need
to do it right and it's good I know it's
fun the only thing is when you work on
our project you don't want to actually
work with an array where you create this
structure by yourself and that's where
they thought hey can we just create an
API and the beauty is it actually
introduced in the second version of java
1.2 The Collection API where you can
actually work with all these data
structures apart from this we also have
linked list right so you can work with
all these things by using some inbuilt
classes so it makes your work much much
easier and also when you want to fetch
data when you want an expandable array
that's right the thing is the attic
which we have worked with it is fixed
size example if I create an idea of size
5 it will be five right you can't extend
it but if you have a scenario where you
want to expand an array maybe you want
an element you want an array of seven
now
uh so of course in the existing area you
can't do that okay now that's one
problem of course you can find a
solution for this as well what you can
do is you can create a new model let's
say nums two
and you can say new
int and you can mention seven here so
you got a new array of size 7 and then
you can copy all the elements from the
above array but the thing is you have to
manually create an array you have to
copy the array and it sometimes it
becomes complex to do all these things
what if you can just get a class or this
feature where you can create an array
which is dynamic right so it's quite
exciting to work with creation API where
you can store data and you can use
different algorithms to work with it
what if you want to sort the array what
if you want to create an array of unique
values what if you want to have an added
to add is one where you have all the
keys one you have all the values
okay so another of course as I mentioned
before in other you can do it but then
what if you can get some API using which
it will help you in writing a code
now that's where we can we are going to
use collection API of course array makes
sense in most of the cases when you know
that the length will be fixed so you
will be using array now whenever you
have a specific requirement of different
algorithms and structures that's where
you will be using collection API okay
now once we know the theory of
collection let's start the
implementation and of course this will
make much more sense once we do it so if
you talk about collection and I'm
talking about the collection interface
now right remember we talked about
collection API which is a concept right
so in this concept we have multiple
classes interface to work with so the
first interface we are exploring here is
called a collection interface and if you
can see the collection interface belongs
to java.utl package as we have seen
before most of the classes which we have
used belongs to java.lank package and
that's why we have not imported them but
if we talk about this collection
interface it belongs to a java.util
package in fact when you talk about all
the collection classes interface belongs
to this package which is java.util okay
so we have to import that as well so you
can do that with the help of import and
you can mention the package name and the
interface name which is collection
now once you say collection you can
create a collection of numbers let's say
and then I can say new okay
now the only problem here is I can't say
new collection right because collection
is the interface right now you might be
saying hey you know it's simple you can
just create Anonymous class provide the
implementation maybe I can try but then
if you can see the collection interface
has so many methods and we have to
Define all the methods see when you talk
about API API simply means a a library
or some feature which you can simply use
it you don't have to implement them then
what's the use of using an API right so
what I will do now is I will remove the
entire part I don't want to I don't want
to Define this method by myself
the second option we have is if you
don't want to create your own class can
we use some in the classes and that's
right we have so many classes available
which you can work with so if I want to
represent this so basically on top we
have something called a collection right
now this is an interface which we are
using now there are certain more
interfaces which actually implements The
Collection one of them is list
we have q
we have set so all these base all these
classes or all these interfaces
basically implements or basically
extends The Collection interface and
individually these interfaces have their
own class implementation example for
list one of the most famous one is at
the list so we can use this for Q also
we have different classes for set we
have a very famous class which is called
hash set so we have different classes
implementation example for Q we have
something called DQ which we can use uh
so for at least we have any list uh
apart from other list we also have
linked list which we can use if you have
worked with data structures before we
have a concept of linked list as well
and then in most of the languages we
Implement them by ourselves right but
then in collection API we get the
implementation in fact inside also we
have something called a linked
has set but then the most famous one or
simpler one is to use other list and has
set for this set now apart from this if
you talk about the concept of collection
the concept I'm talking about collection
API uh we have one more thing to work
with we have something called a map
right and map has multiple
implementation which we'll see when we
start with map okay so at this point
let's try to use either list or we can
use set but let's start with a list here
so what I will do is instead of saying
new collection I can say new add a
list and you can see this is a class
ignore this angular packet I know it is
coming from multiple times but ignore
that time bin so we got this collection
nums equal to new other list now in this
numps basically we can add values okay
uh now how do we add value which is very
simple you can just simply say nums dot
let's explore the methods you can see uh
we have method like add we have methods
add all contains uh equals for each okay
we'll say for each as well which is very
interesting uh then we have notify
notify all uh remove then we have we can
also convert a collection into array we
have to add it there and then we have a
weight method but at this point I just
want to add the values right so I can
just come back here and I can say add
and in this ad I can add values so let's
say I want to add value which is 6. so
since this is numbers I'm expecting that
this will only have numbers so I will
just copy this code and I will try to
add multiple values so let's say this is
5 this is 8
and this is 2. so basically we got this
value right now ignore this uh yellow
zigzag lines here we'll talk about that
later okay but yeah that's an important
concept which is coming up but at this
point I got this collection right and I
want to print this now if you have an
array of course you can also get array
with this elements but the problem there
is you need to you cannot simply print
an array right you have to use a loop to
print each element but that's not the
case with collection I can simply come
back here and I can say s out and I can
print nums and you can see if I try to
run this code
if I say
compile
okay so when you compile this code
there's no error but you can see there's
a warning here again we'll talk about
that watching in some time but let's run
this quota and see what happens and you
can see we got the output so we can
directly print a collection that's a
beauty okay uh can we print this value
one by one actually we can okay so what
you can do is you can use a loop here so
I can say for
we can use index values let's let's see
if do we have index option here so
against the nums dot uh if I say get or
unfortunately we don't have the indexing
for collection API or collection
interface here no issue I can use uh
enhanced for Loop remember we have used
enhanced model with the loop so I can
say int and colon nums
and I can print each n value so I don't
have to do this again how do we use
index that we'll see later but at this
point this should work
okay the only problem here is okay let's
let's talk about the problem which we
are getting this great uh this yellow
line here so the thing is when you talk
about a collection when you're getting
nums here right see in Array you specify
the type as well you say eight nums
right so you know that in this Nubs
you'll be having only integers
but when you talk about collection
nowhere we have talked about the type of
it
how it will work okay and that's where
what you have to do is you can mention
the type and that's the error you're
getting here because it says the values
which I have added here is not actually
numbers this are object type that's
right
uh as we talked about integer float
classes all these classes basically
extends the object class and by default
The Collection API works with objects
and this 6 5 8 2 they're not integers
they are objects and that's why you
cannot store that into integer how do we
solve this problem so if you want to
solve this problem we can use a concept
called generics
okay now how it works so basically where
should we mention the type
maybe what they could have done is you
know this is what they have done in 1.2
1.3 1.4 but the realized one problem
right which is by default all the values
here are objects
so how do we specify maybe they could
have created some extra classes by
saying integer list integer collection
string collection what if you have your
custom class like student so it will be
difficult for them to create all the
classes right so what they did is they
have given you one option where you can
use angular brackets here so just after
the collection use the angular bracket
and in that you mentioned the type of
element you want to work with so we are
working with integers so integer is
basically a class
ah which is the vapor class for the int
type because int is primitive integer is
a class and collection normally work
with objects not the Primitive values so
if you want to store integer numbers
which is you have to use a class integer
and you can see now there's no problem
there is no yellow zigzag lines and we
got the there's no error here as well
let's see if this works I will say
compile and
run and you can say we got the values
now one more thing why this type here is
so important see it also helps you to do
to remove the bugs of your code now what
bugs it can be example let's say if I
don't mention integer here okay let's
say remove if I remove this part and
everything is object right and then here
what I'm doing is I am
uh we can use an answer the only thing
is I can't use object here I have I
can't use in I have to use object and
then I am converting this object into
integer so we can do that by typecasting
it here so I can just type casting it to
integer in fact we can do it outside as
well let me just do that so I will say
int num is equal to I'm getting a num
variable again and I'm converting this n
to the integer type okay so you can see
we got num and what if this with this
num I'm performing some operation
because I want to perform the operation
that's why I can't use object
and now if you try to work with this you
can see again we got the warning because
we are not using type there and if I run
this code it works there is no problem
but what if by mistake you are doing the
code and you have added a number but
that too in double quotes
let's say five
now what will happen Okay so let's see
if I compile this code there is no
problem if I run this code we got an
exception and it's bad right and this is
also runtime exception this is runtime
error basically we don't want this and
that's why I think this type of problem
should come in compile time itself so if
you mention the type with the help of
generics here
and if I mention integer here as well
now if you can see
we will get the compile diameter not run
time error and that's why if you compile
this code
okay you can see we got a compile time
around and that's why it is better to
put this type every time so whenever you
work with collection always mention the
type there
cool so that's how we use analyst and it
has multiple methods now the only
problem is we are not using the we are
not able to get the index value right
see the thing is if we talk about
analyst as I mentioned in the diagram as
well analyst is a class if you can see
here so it's basically a class which
implements a list right and if you talk
about this list list does have a method
called get because list works with index
in the values
so which one to use should I use a
collection here or the list so if you
want to use if you just want to add
values and fetch collection makes sense
but if you really want to work with
index value instead of collection we
should use list because list supports
index value and you can see now I'm
working with
uh list here and now if I want to print
a particular index value let's say I
want to fetch the second index value
so I can say nums
dot get as you can see we have a get
method and in this get you can mention
two so which is it will in fact it will
give you three it will give you eight
which is at index number two right let's
try I will say in fact let me just not
print this Loop compile
and okay run and you can see we got
eight so if you want to work with index
you can use list and list has some extra
methods if you can see against a nums
dot add was that uh we got get we can
also set the value in between with index
value and anything else yeah we also
have index of
so if you have an element if you want to
know the index of it example let's say I
want to see I want to find the index of
this two value so what I can do is I can
say s out
I will say nums Dot
index of I want to print the index of 2.
right so 2 I'm talking about the value
now or maybe you know this is this looks
like quite confusing so I will say five
so index value is one if I compile and
run you can see we got one there so yeah
it has multiple methods and I would
recommend you to explore more methods of
list and that's how you use what you
work with list and other list now to
this point we have talked about least
right now list is one of the collection
API concept it it supports index values
right so we can create a list and we can
work with indexes there the only thing
is when you talk about list of course
it's great uh it does support multiple
values example let's say and that's a
feature now I'm not talking about the
drawbacks of it so I can say I can add a
element let's say six again if you can
see I have two I have two elements with
the same value which is six now if you
are wondering what is this e here again
this is given by my vs code it simply
means element and if you see if I try to
run this code if I compile this code and
run you can see okay we're not printing
all the values is it no we're not
printing all the values so I will just
remove this two lines and focus only on
the for Loop here and let's see if this
works now so I will say compile and run
you can see we got oh uh I guess we are
doubling as well right anyway you can
see we have a list which has same values
so yes your list does support repeated
values but sometimes you want to have a
collection where you can only have a
unique values remember when we talked
about the collection as an interface it
is also extended by a set interface Now
set supports unique values okay so what
I will do now is I will have the same
values okay but the instead of using
list I will say set and let me import
the package for this I will say control
space enter and we got a package for set
as well and then I want to specify not
an analyst okay because I see the thing
is if we talk about set yes set extends
collection but the class which
implements set is different and the
class name is Hash set okay I can import
the package for this as well and done
apart from this the syntax will remain
same we also specify the type here the
generic type which is integer and okay
let me remove the list input let's only
have set and has set and you can see we
can have the same method add also here
and we can print all the values the only
thing is here I will be very specific
that I am working for integers
um let me remove this and I also want to
print the value now that's it
okay now when you have these values let
me just compile and run you can see now
the value is 2 5 6 8. first of all we
can't have a repeated value you can say
six and six uh we only got 1 6 here the
second thing is it is not following
these sequence remember the if you can
see the sequence is six five eight two
but we are getting the values in sorted
format is it really sorted let's try
what I will do is I will just make this
okay first of all we know that we cannot
have repeated values I mean we can add
it it's just that it will not have the
same value again uh let me just make
this as 54. I will make this as 82 I
will make this as 21 and this is let's
say 62. again we have a bigger values
now let's see if that really is sorted I
will say compile and run
if you can see it's not actually sorted
it's 82 21 54 62. okay this is not
sorted and it is not go even going for a
sequence and that's how this set works
set will not give you value in this
sorted format okay it basically uses uh
and it also doesn't have a index value
example if I say nums dot for at least
remember we had a get here we don't have
get I mean we don't have a get which
takes element we do have a get class but
we don't want it we want a get method
with using which you can specify the
index value set does not support index
value
so certain things to remember for set so
set basically is a collection of a
unique value if you see documentation it
says a collection that contains no
duplicate elements and uh it does it
does not even have uh index value is it
not mentioned anywhere
anyway so you can't have index value I
know when I mentioned about collection
API it was introduced in 1.2 and also uh
it is also called collection framework
okay instead of saying uh API you can
also say its collection framework cool
um so this is your set and that's how it
works what if you want a sorted value so
instead of using hash set we can use
something called a tree set so let me
import the package for this
import
and now if you try to work with this
so you can see we got all the sorted
values so basically this tree set
actually extends if you see it extends a
abstract set and implements a
navigational set
and if I go to navigational set you can
see this interface actually extends a
sorted set and that's why all the
elements in this tree set will be sorted
okay it is a set but then it is sorted
set so it depends upon what type of
elements you want to work with if you
want to trace a particular element then
preset makes sense but if you want to uh
want to have a set which will have only
unique values there is no need for
auditing you can go for hash set there
one more thing instead of saying set
here we can also say collection even
that works in because anyway uh the tree
set implements set and set extends
collection right so we can use that as
well one more thing to add if you if you
look at collection and if you look at
our diagram on top of collection we have
one more interface which is called
iterable
uh since we can iterate between the
elements right with the help of enhanced
for Loop or different we have different
options so it actually extends a tribal
and if you go to a table we have an
option called iterator so that even that
is one option you can use iterator
method which will give you a iterator
itself let me show you how that works
instead of using a for loop I can say
nums Dot iterator
right so we got the iterator now this
iterator will return will give you
iterator back the Twitter object
I would say this iterator is integer I
will import the package and here I can
say
uh values equal to so from this iterator
I got all the values here and then from
this values I can print the values
I know that sounds weird right but let's
do that I'm not using a for Loop so how
do you print all the values so basically
values has a method called has next and
it also has a method called
uh next which will give you the next
element
okay it will give your next element but
it will only give you one element right
I can put that in a loop to get all the
elements
uh but which Loop we have to use in fact
what I will do is I will just try to
plant
this next element
but the problem is it will only give you
one element how will I use a loop here
because if I use a loop I need to know
how many elements we have right so one
thing we can do here is we can use a
while loop because it has a method
called values dot has next now has next
will tell you that do we have a next
element okay and let's try if that works
compile and run and you can see we got
the values so even this we can also use
iterator that's also an option and
that's why we got the top most interface
which is iterator
so that's how we use set a Twitter and
reset we can also try it with the linked
has set but then yeah internally they
work differently but you can get the
values okay so we have talked about
least we have talked about set of course
we have different classes as well for
different structures and this is a
famous one now there is one more which
is called map Now map is not an
implementation or it does not extend
collection interface but it's a part of
collection concept relation API right so
what I will do now is let's work with
map here but why do we need map see the
thing is when you work with list let's
say we have a list here and list of
values we have okay so we have list of
values let's say the values are 56 23 67
and 92. now we have this badges right
and let's say uh if it if you work with
analyst here if you work with list
basically for this values if you want to
work with these values you need to work
with the indexes why do you have to say
0 1 2 3 right but sometimes it's better
to have a name or a different kind of
index instead of having zero and one two
three uh example let's say if you talk
about phone book we have a name and a
number right so can we have something
like this I want to say these are my
students marks right so I want to say
this marks belongs to Naveen uh this
marks belongs to let's say hush uh this
marks is belong to social
and we got Kiran so instead of having
index value can we have a name to it
okay instead of having this values so
can we do it and that is possible with
the help of a concept of key and a value
pair so we have a key and a value so
example this value which is 56 23 67 92
there are values and the key for this is
Naveen the key for this is Hersh the key
for this is social and the key for this
is Kiran right and we can achieve this
two things in one data type or data
structure which is called a map
so this map map is basically a
collection of not map is a collection of
key and a value pair how do we achieve
that so what we can do is we can remove
the entire section from here just to
keep it clean and let's work with Okay
we don't even need these Imports now
so let's create a map so where you can
create a map is map and okay let's
import the package for this again
java.utl and we can say this is students
that's a map of students and new Now map
itself is an interface if you can see
and it supports key in a value pair now
if you remember when we talked about
analyst it was having either right
because it represents elements in map we
have KV it is just a character
representation of what you are going to
insert now this key this K and this V
can be replaced with data types like
string integer integer float or we can
have student
string whatever type of you want to work
with so now we have to look for a class
which implements this so the class name
is hashmap right and in this as well we
have to mention the type of it the type
of key we are working with is string and
the type of value you're working with
here is
integer okay and of course it can be
anything it can be string student it can
be storing string that's your choice
whatever data you're entering but we got
this map here now once you've got this
map I can simply add some values here
how do we add values it's very simple
you say students dot now we don't have a
add method we have a put method so we
have to use put and we can specify two
things the key in a value and as per our
diagram we have seen the key I want to
insert is Naveen and the value is what
56 and likewise we can have all the
values here copy paste paste paste and
this is hush
and the value here is 23.
this is social
the value is 67 Kiran it's 92. so we got
all this key and a value right and then
if you want to print it you can you can
actually do it before this we were using
list and then for every value here we
were using index but now we have a
logical name to it it is much easier to
work with names right
uh so I will say s out and here let me
print these students
basically I'm printing the map itself I
will compile this code and run and you
can see we got a map we got Naveen 56 we
got social 67 we got killer 92 and hers
23. now one thing to observe even this
is not following a sequence you can see
we got Naveen first then we got social
we got Kiran we got harsh okay it looks
like more of a set right let's Explore
More uh okay so we can do that otherwise
if you want to fetch a particular
student only one student you can say
student dot you can say get and in this
get you can specify the key let's say I
want to get the marks for not all the
students but let's say hush I can
specify the key here
and if I compile this code and run you
can see we got 23 that's the marks for
hush
okay we can do that okay one more thing
I want to print all the values
but then what I will do now is let me
say during my school days we used to
after the exams when the paper is
checked we used to get the paper back to
calculate the marks right so we used to
turn the page we used to calculate each
and every marks and at the end once we
add all the values of all the marks of
each question if that marks is more than
the marks which you got on the paper
which is checked by your professor we
used to go and collect it right of
course if you got extra marks then you
don't go there but let's say uh has got
23 and after calculation we have changed
it so let's say students.put
and now I'm saying hush and the new
value is let's say 45. there are a lot
of mistakes in the paper so let's say we
got 45 here now tell me will it add a
new student as hush or will it replace
the existing value let's see what
happens
if I compile this code and if I run you
can see for Hirsch we only got one Hersh
here which is 45 we don't have two hush
that means the key cannot be repeated
keys are unique the values can be
example I can have two students with the
same number and of course we do get same
marks right if you copied anyway so we
cannot have keys repeated
so can we say these keys are actually a
set
that's right and the values are least
here so we have a set and a list
combination to get to get a map here
okay so what I want to do now is I want
to print all the values and that's why
you can see there's no sequence here
because it's a set okay I want to print
all the values but one by one I want to
use a for Loop here can we do it the
problem is we don't have see if you work
with list and if you use a for Loop it
will give you one value at a time right
there's no one value here we have two
key and a value so what you can do is
first of all let me just get all the
keys and let's see how it works
I will say students I want to get all
the keys so do we have a method which
will give me all the keys if I go down
down down yeah you can see that we have
a key set oh we were right it's a set uh
so I'm printing all the key set now so
if I compile this code and run okay so
that we got all the keys
if key set gives me all the keys
if I run a loop on this if I say for
what type of case set it's a string
right so I can say string Name colon it
is coming from
students.key set
okay so what I'm doing is this key set
will give me a set right and from that
set you are fetching one name at a time
and with that name I'm printing first of
all name as it is
and I will give a space in between or
maybe a colon and then I can provide the
I want to get the value how do you get
the value so you can say students dot
remember we have worked with this get
and you can pass the key which is name
of course right your key is in is in in
this name or maybe I can just to make it
simple instead of same name I can say
key itself and here as well I can say
key
here I can say key
right simple and now compile
Run Okay so that we got key and a value
there so that's how you can print all
the values from a map now why we are
using our put method here is because
when we say add we are adding new
element when you say put it says try to
add the element if you already have this
key just replace it let's put
okay apart from this do we have some
more methods to explore so if I say
students dot we got a put we can also
say get if we can also get values all
the values the way you have key set
which gives you all the keys when you
say value it will give you all the
values uh apart from this we can use uh
remove to remove the particular element
or the particular entry or we can
replace as well yeah those are the
methods we have and please explore those
methods to understand this mode
so that's how basically you can use map
in fact apart from this we also have a
hash table
so if you can see we have hash table
here and both works almost same if you
compile this code and if you run this
you can see we got the same output so
what's the difference between hash table
and hash map if you go here and if you
go on top
okay so if you can see in the hash table
code it says the new collection
implementation which is Hash table is
synchronized now it depends upon which
you want to use so if you want to use a
synchronized version you can use hash
table if you want normal we can use
hashmap now what is synchronized if you
remember we have worked with threads so
if you have multiple threads working
then it's better to use hash table to
make it synchronized right so if you go
up
let's go to hashmap to see what it says
so if you go to Hash map
okay it says if you want to work with
multiple threads and if you still want
to use hashmap then use synchronized
externally so if you want to use
synchronized use hash table otherwise
Map works
so yeah that's how basically you can use
map and uh that's how you can fetch the
values in this video let's try to work
with sorting so let's say if you have a
collection and you want to sort it how
will you do it so first of all I will
create a list of values I will say list
of uh I will say integers this time and
then let's say nums equal to new add a
list right and then we can import this
okay now one thing to observe when you
talk about this type here on the left
hand side there is no compulsion to add
that on it inside okay at the start when
generic concept came it was compulsory
for us to assign the values or to set
the type on both the side but after 1.7
they have kept it optional if you
specify the left hand side on the right
hand side you can simply keep empty
bracket that completely works okay so in
this added let me add some values I will
say nums dot add also four and likewise
let me add some elements here
okay so let's say we have these values
here and what our do is of course if I
print this value so it will be printed
as it is and it follows the sequence as
we have seen so if I compile this code
and
run you can see we got the values now
what I want is I want to sort this
values how do I do it now we have a very
special class called collections okay as
I mentioned in the first video uh we
have a collection class as well and this
collection class has lot of methods one
of the method is called sort and in this
sort you can pass the array or address
which you want to sort okay now
collection class belongs to util package
okay and then once you say sort and
after that if you try to print these
values and let's say the output if I run
this code you can see we got three four
seven nine so sorting is actually very
easy in terms of collection here right
now thing is what if you want to sort
this based on your own logic how will
you do it example let's say the values
are 43 uh 31 and then 72 and 9 or let's
say 29. so we got all these values right
and then I want to sort them based on
their last digit not the entire number
because again if you sort this value it
will be sorted based on the values right
I want to sort based on the last digit
so I want 31 to be first and then I want
42 then I want 72 then 43 then 29 so
this one first then this 2 then this 3
and then this nine how do I change a
logic here say by default sort will take
its own logic right in case if you want
to have your own logic in that case what
you can do is we can use something
called a comparator as you can see we
have a comparator here okay how do I use
it so if you talk about comparator let's
try to use comparator here so if I use
compare it vector and if you go there
comparator is basically an interface
okay so how do I use comparator so I can
say comparator comp is equal to new
comparator now this is an interface
right and we know we have multiple ways
of implementing an interface we can
create a class which implements the
interface or we can use something called
an anonymous interface Anonymous class
here
okay this comparator works with integer
and I can specify that here as well
which is integer
in terms of anonymous class such as
compensate to specify on the ident side
as well okay we can use this comparator
here and in this I will Define the
method which method we have in
comparator so if you look at this
comparator we have a method called
compare okay that makes sense we can use
compare here
uh what's the Syntax for compare it is
okay not this one
the syntax is int compare and pass the
two values so T is a type here so
integer integer okay so I will say
public int compare
and we have to specify two values
basically one is your uh I will say int
I comma ain't J see when you basically
sort the values you know normally you
compare two values example let's say if
I give you uh four values here two three
let's say we got four we got three we
got one we got six if I want to sort
this at one time I will compare two
values I want it to be ascending order
so smaller value come first and then the
bigger value go second so I will compare
these two values if the first value is
greater than second value I will swap so
after swap it will be four three oh
sorry three four one six then I will
compare these two values uh then it will
be three one four six then we'll compare
these two values so this will be three
one six or sorry 346 because the first
value is smaller than second value no
swap in this case we have swapped it
because it was a bigger value now once
you got one of three one four six we'll
do this iteration multiple times again
if you compare this two this will be one
three four six then this two it will be
one three four six
now we don't have to do that we don't
have to compare the last two because in
the first iteration you know the biggest
value comes at the end so we got we got
that right so we have to do that only
three times and again for the next
iteration we can say one three I know
this is sorted but still we have to
continue the iteration first compare one
first two one three four six and you're
done
right so this is how basically you sort
the elements the the aim here is when
you sort elements uh this is one of the
algorithm for sorting basically we have
to compare two values and swap that's
basically basic rule right so here as
well when you say you are sorting you
have to just sort of specify when to
swap and not to swap so when you compare
I and J
if you say okay now we want to compare
and how do you specify that we have to
swap so if you return one it will swap
if you return minus one it will not swap
it's that simple
okay so what I will do is I will I will
check and I want to check the last
number right so I will check if how do
you get the last number oh mod 10. if I
mod 10 is greater than the J
mod 10 in that case swap else you can
say return
-1
okay so this is how basically you
specify the logic and I can still see an
error here what is the error the compare
method is correct okay there should not
be any error here okay let's see what
happens so what I will do is I will pass
this com object here itself I will say
com
and okay there's still an error
I don't see any reason to get the error
did I forgot any colon or something
things are looking good let's compile
this one let's see what happens compile
there is an issue is not abstract does
not override
okay it is giving an issue with the
compare method is it the right method
when I'm using compare okay that's right
okay do we have to use the class names
here
integer and integer oh it was because of
the class name my bad yeah so we have to
use a class email right because
collection works with the vapor classes
and now I will try to compile this code
and okay compile two times
and run you can see we've got distorted
values we got one two three nine so
basically what we are doing is we are
changing the way it sorts the value if
you want to specify your own logic we
have to pass an object of a comparator
now in this object relation of
comparator you have to specify the logic
on based on which you want to sort this
uh in fact let me give you a challenge
here what you can do is instead of
creating the list of integers create a
list of string and sort this string
array with the help of the length of the
string okay that will that will be
awesome right try that
this is how you sort the value based on
the comparator so what what is
comparator basically so comparator is a
concept or an interface using which you
can specify your own Logic for sorting
okay
that makes sense right now I will do
something else here what I will do now
is instead of having a list of integers
let me have a list of students okay so
what I will do is I will get a class
here called student and
let's say we have int age for a student
and string name and I also want to have
uh two streamers so that I can print the
object as it is so this is Source action
I want to get a two string method name
because I want to print the student
values as it is and let me also have a
Constructor using which I can assign the
values to them
I will say Source I want a Constructor
which can take both the values okay this
makes sense let me remove this at
override for time being okay so we got
the Constructor we got two strings what
I will do now is instead of creating a
list of integers let me create a list of
students I will say student here
and then because that type of student
right and we cannot add numbers now I
will say these are stoods
uh to replace this with stoods
or maybe let's have numbers what's an
issue and then here instead of adding a
number we have to add a student right so
I have to say no student and this will
be value one or let's say we have to
specifying age right let's say age 21
and name is let's say Naveen then let me
just create some more objects here so
let's say age 12 name is let's say John
and then H we got here is 18.
let's say puddle
and we got age 20. let's say this is
Kiran okay so we got this four student
here with different age and different
names now what I would do is I want to
sort them okay timely let me just
comment this section I want to print the
edit as it is and let's see what happens
if you compile and run you can see we
got all the values the only thing is
they are getting printed in a weird way
I want to print them one by one so we
can use a enhanced for Loop here so I
can say student as Colon's nums and we
should have used studs there
now what I can do is
I will replace numps with stoids okay
this should solve the issue and done
okay so we got some students and I want
to print one student at a time let's see
if that works
compile and run okay so we got all these
values now what I want to do is I want
to sort these values based on their age
how will I do that
in that case I have to say sort okay let
me just try natural sorting the moment
you do that it is not working can you do
that with the sword weather is not
working
okay let me pass the comparator object
the only thing is now this comparator is
not working with integer it is working
with students so it is a student now and
both this object so again we have to
compare two students right so we need to
show it at a time so I will say student
and student
let's say this is I and J now how do we
compare them we are comparing that age
right
so we have to say I dot h is greater
than
J dot h then swap
it's so simple right
since we have worked with the integers
it should work normally and if you want
this code okay so that we got all the
students with the ascending order of age
we got 12 18 20 and 21 this works right
so this is how basically we can use
compat and we can sort a student as well
but there's one more thing
why we have to pass a comp here why not
if I just say student white is not com
why it's not sorting it's because this
student we have not specified the logic
for the student right because if you go
to the integer class let me just type
integer here just to see if you go to
integer class you can say integer class
Implement something called a comparable
and by that's why by default the sort
works with integers our student is not
implementing comparable so if you want
to have a natural sorting you can also
Implement something called a comparable
the only thing is this compatible
interface has a method called compared
to okay so we have to Define that method
so I can just come back here and say
implement this comparative method
this is the signature
okay and we are comparing this with a
student itself
and let me say this is that okay the the
name of the variable is that will I will
tell you why I've said that but now what
I'm doing is I'm adding a method called
compared to
and I'm implementing something called a
compatible now and then this comparable
actually works with a student we have to
mention that as well now if you go back
you can see there's no error now so sort
method does work with student provided
you are implementing comparable if you
if your students are not compatible how
you can how can you sort them that's
what it says but then if you try to
compile this code and run it will not
work the way we want it you can see this
is not sorted
and if we are not using compared to now
I'm not using comparator what I'm using
is I'm using compared to off compatible
so whatever logic we have written here
the same logic I have to write here
okay now the only thing is we have to
compare two students right
one student is that so we can say this
is that what about the first student the
thing is we are defining this method
inside the class itself right so what we
can do is we can say this remember this
keyword current object so this dot age
the current object the current student
we are comparing the current student
with the other student it's something
like when we don't have a compatible and
if you have two students here we need a
third person to compare two students but
now I'm giving this power to the student
itself they can compare themselves so if
I'm comparing with someone else
I'm this and that is that
okay and let's see if that works now
compile and run oh it works inside we
got 12 18 20 21. so these are basically
we can use compatible and comparator so
you have two choice either you can make
your class implements compatible if you
don't want to do this you can also use
comparator
in fact even if you mention comparable
you can still override the logic by
comparator that's your choice okay one
more thing before we close this let's
say I want to use comparator here if a
pass comparator and I want to you I want
to reduce this code remove a Lambda
expression this is a functional
interface we can use Lambda here as well
so what I can do is I can remove this
entire part from here to here I know you
have to watch this video multiple times
to make it work uh I can put an arrow
and we can put this curly brackets as
well
one more thing instead of using IF else
we can also use a title operator here so
the same logic I can just comment this
part I can say return I dot h is greater
than J dot h return one otherwise return
minus 1. so instead of using IF else I'm
using turn it operator we can remove
this part now since we only have one
statement and that to return we don't
need return that is optional we can
remove curly brackets as well and we can
write everything in one line again watch
this video multiple times to understand
what I'm what I'm doing here and also in
the Lambda expression you don't have to
specify the type you can simply say I
and J
and your job is done you can see that
entire comparator went into one line and
that's why functional interface are so
important
let's see if this works and what I will
do is I will just remove this from
comparable
just to see if that works without
implementing compatible Implement run it
works what is comparator if you want to
specify on which logic you want to sort
the elements you can use comparator what
is compatible if you want to give a
power to the class itself to compile
itself or to compare its object to
itself we can use uh compatible there in
this video we'll talk about stream API
now before we understand stream API
first of all it's a New Concept it came
in 1.8 Java 1.8 basically and it
provides some amazing feature the only
thing is why do we need those features
we'll understand that first so what I
will do is first of all I want to create
a list of values okay so let's create a
list here and I will say this is of type
integer and I will say nums and of
course just to keep it simple I'm going
with the default names so that you you
don't have to focus much on the naming
convention I want you to focus on the
concept so we have the analyst here and
in this at least I want to have some
values we have nums dot let's add some
values I would say add four in fact you
know what I'm going to do instead of
adding values like this there's another
another way you is using which you can
add values in the list uh which is
there's a class called arrays and arrays
dot as list and you can simply pass the
values here instead of manually typing
the values even this works so as list is
a method which gives you a list and it
belongs to a class called arrays okay
this is much simpler right now once you
got this list what if you want to print
these values of course I can say s out
and I can say nums and if by doing this
we can simply print all the values and
you can see we got all the values now
what if I want to perform some operation
on this okay now what kind of operation
I'm talking about so let's say I want to
uh double all these values and in fact I
want to First apply the filter here so
let's say I don't want odd numbers I
only want to focus on even numbers
example we have 4 and then we have two
ignore this dot dot a basically it
represents an array so we got this 4 and
2 I want to filter them and whatever
filter of whatever value you get after
filtering I want to double those values
so example 4 and 2 becomes 8 and 4 and
at the end I want to reduce it so I want
to say okay 8 plus 4 is 12. so I want
the output to be 12. the way you can do
that first of all I want to apply the
filter right so we can use a for Loop
and we can go from the first row to last
value so I can say int n colon from nums
and once you get this value I want to
apply the filter because see I don't
want to add all the values I want to add
only the odd numbers and that to have to
doubling it I want to add even numbers
basically so we can check if my n mod 2
is equal to equal to 0 that means that's
a even number if that's a even number I
will first of all double the values I
will say n is equal to n into 2. so
doubling done and then once you have
doubled it I want to add it into a
to a sum let's say I will create a in
some variable the initial value is zero
and whatever doubling you get you simply
say sum is equal to sum
plus n okay uh so by doing this what I'm
doing is from all the values which we
have here let's say we have some more
values let's say 6 as well and let me
add one more value here which is three
so you can see we have so many values
but I want to first of all filter only
even numbers the example I want to fetch
this 4
uh then just 2 then this 6 I want to
Double H value so example 8 plus 4
becomes 8 2 becomes 4 and 6 becomes
twelve so this is 8 plus 4 is your 12 12
plus 12 is 24. I want the output to be
24 and let's see do we really get 24
here let me print the value for sum
compile and run and you can see we got
24. now this is one way of Performing
the operation on your list now sometimes
you perform such an easy operation and
sometime maybe you do something by using
which the values in fact the original
values gets changed so instead of doing
those things uh we got this amazing way
of doing this calculation which is
called a stream API now it was
introduced in uh in later version before
this people used to work with this way
but in in stream we got a different way
of doing this okay now basically we got
this new thing which is called Stream So
if I jump to stream which belongs to
java.utl.stream package and if I click
on stream you can see stream frame is an
interface and it provides you multiple
methods like we got filter that makes
sense right if you want to apply the
filter on the stream or the collection
we can use filter if you want to change
a value example we have doubled the
values right that can be done with the
help of map
and we'll individually see this methods
later
so if you go down you have sorted in
fact there is also a method called
reduce we are going to use that as well
as well okay we'll see that later so
basically stream provides a lot of
methods to work with this now how
exactly do you stream that we'll see in
the next video but before that I want to
show you one thing select so let's say
we got we were able to do this right at
this point I will just determine this
section because we'll talk about that
later I want to do one more thing before
we start with stream which is how do I
print all these values a simple
splinting so we can use a normal for
Loop right the normal for Loop Works in
this way we can use int I is equal to 0
and int are a less than uh we have to
get the nums dot length or size yeah the
method name is size and then we have to
say I plus plus so we have basically we
have to use normal for Loop and then we
can print each value I can say num start
get I can pass the index value
and if I clear this compile
and run and you can see we got all the
values here okay there's one way
I can comment this section the another
way of doing this is using a normal for
loop I can say for
int n is equal to num and here
I can simply print the value of num even
this works
right now you tell me which is better
using a normal for Loop or the enhanced
for Loop see normal photo what it does
is it basically goes to the loop oh it
basically goes to the list by saying Hey
I want to fetch the first element I want
to fetch this second element right on
the other hand if we talk about the
enhanced for Loop it says the array
itself will give you the value and that
value goes into n right now again this 2
looks good but then we have a better way
of doing it so I can just comment this
section the better way is very simple
what you can do is you can say nums dot
now we got a new method called for each
method Now using this for H it will give
you one value at a time you can save
that in n
and then you can simply come back here
and you can say I want to print this n
here so for each is a part of the list
interface you can simply say for each
and then it will give you one value and
you can do whatever you want to do with
that value so I'm just printing it here
in here
and if I compile this and run you can
see we got the same output so we have
three options now we can use a normal
for Loop we can use the enhanced for
Loop or we can use a for each method so
let's understand what this for H and
what is this statement inside this this
looks weird right yeah I know we have
worked with Lambda expression it looks
like Lambda expression but what is
happening behind the scene to understand
that what I will do is I will just
remove the entire formula we don't need
that and let me just push this down
this will be required later once we talk
about how do we stream API but at this
point let's only focus on for each year
so what I will do is first of all I will
remove this section or maybe I can just
comment it so that we can use we can see
this later
here at this point let's try to use nums
so when I say nums dot you can see there
is a method called for each now for each
method if you see and if you go to this
definition for each basically got
introduced in 1.8 okay and what it
basically does is it takes an object of
consumer you can see for each method
okay let me just go to definition itself
so you can see for each method takes an
object of a consumer okay that sounds
weird right let's see what this consumer
is so if I want to work with foliage I
need to create object of consumer okay
so the moment you say you have to get
object I can simply say consumer and you
can see consumer is a interface
which belongs to our package
java.util.function okay that's new and
this is a interface which is a
functional interface that means Lambda
expression will be applicable and the
only method we have to work with this is
accept okay that means I have to create
object of consumer which takes the type
of integer because if you see the
consumer interface you have to specify
type as well
so I would say consumer integer and then
I will come back here let me say
con is equal to how do I create an
object of it it's very simple you can
say new consumer
now since this is the interface we have
to define the class which is anonymous
class
okay that is also simple the only thing
is we have to define a method also the
method name is public void is it white
let me just check once consumer has a
method called accept which is of type
void okay which returns a void and the
method name is except I will say that
and then it takes the integer value I
mean whatever type you mentioned I will
say integer let's say n okay now the
thing is once you got this consumer
object you can simply pass an object in
this I can simply say con so for each
needs an object and we are passing the
object of consumer our job is done right
the thing is when you talk about for
each what it does is it gives you one
value at a time okay now whatever value
you are getting here or for it is giving
you that goes into this consumer object
and the consumer object has only one
method which is except
okay now this except will accept a
number that's right the forage will give
you a number right that goes into this n
now you can decide what you want to do
this with n okay I would say I want to
just I just want to print it I mean
that's your choice you can do whatever
you want to do with this n at this point
I'm just printing it okay and now let's
see if this works I will just go back
and clear the screen compile
run and you can say it's working you you
are able to print all the values
okay and you can see the entire code all
the other codes are commented so they
are not running this code is running and
it is printing all the values makes
sense
now we also know that the consumer
interface is a functional interface
which means we can use Lambda expression
here that also means from here to here
we can delete this part let's delete
that let's delete this curly brackets
and I hope till this point you have
you've got a Mastery in Lambda
expression and I can give a arrow here
that looks good and since we only have
one statement you don't need to put
curly brackets I will remove that as
well and I can write everything in one
line that looks cool right
and then we don't even have to mention
the integer here and we don't even have
to mention a bracket when you have only
one variable
makes sense right
let's see if this works after doing all
those changes compile and run there's no
problem now what we are doing is we are
assigning this expression to con right
now whenever we have con we can actually
use this so instead of using con here I
can simply use this particular code and
replace this Con and that's it
we don't even have to create a reference
for the consumer and this is what we
have seen earlier right if you compare
the Urgent example this looks similar in
fact exact same so that's how your for
each works it gives you the value that
is your n and you can do whatever you
want to do with that and you can print
it you can add it you can save it in
database that's your choice
okay so that's how basically we use a
forage now once you understand forage
let's go for the actual stream API so
basically we were we were having this
collection or at least right where do we
have values and then we were able to
print that with the help of for each and
now we know what is happening behind the
scene right
what if you want to do this with a
stream API now let me just give you the
introduction of stream API here and how
it looks like so if we talk about stream
stream is an interface right so if you
can see uh we have seen that before as
well stream is basically an interface
right the thing is if I go back to nums
and if I say dot you can see now in the
list we got this new method called
stream
again before 1.8 the method was not
there it was introduced later but we got
this method called strain now what this
train does is it gives you or it Returns
the object of stream okay so that means
if I want to accept the values I can say
stream of integers and let me just name
this as S1 so this is our stream which
is called S1 here and we got all the
values so whatever values you have in
this list is available in this S1
now with this stream you can perform any
operation and the beauty is it will not
going to affect the nums so whatever
changes you make to this stream if you
change the values if you double the
values it will not going it is not going
to affect nums now why this is important
see sometimes when you have a data and
then if you want to perform some
operation it's not like always you want
to change the existing values remember
when we talked about threads when you
have multiple threads and then you are
performing some operation mutation it's
not good right so whatever changes you
want to do do that in this stream and
use it at least you have your original
values with you
okay now that means I can also print the
entire thing with the help of for each I
can say S1 dot for each mind you again
in this stream of S1 we got all the
values which are there in the list
and let me describe that works I will
say compile and run and you can see we
got the values here
now one of the thing about stream is
once you use the stream you can't reuse
it and that's why the name is stream
example if you talk about the flow of
water the stream right once example if
you let's say if you're sitting near the
river or the bank of river basically if
the water passes you can't retouch the
same water in the same way once you have
worked with a stream you can't reuse it
example let's say if I try to print this
multiple times let's say two times
it will not give an issue with the list
okay you can simply say nums dot forage
multiple times there's no issue but if
you try to do that with the stream once
again you can see you will get an error
compile time there is no issue run time
it will work once the second time it
will say uh the stream has already been
operated a pound or close that means you
can use stream only once okay uh that
makes sense so we can't reuse it but
then what is the benefit of using stream
here the benefit is stream provides you
a lot of methods to work with example if
I say S1 dot uh we have methods example
we have methods like filter remember
when we talked about the other example
where we were removing all the odd
values or we wanted to only get even
even numbers we can do that in stream as
well now how it looks like
I can simply say S1 dot we can use a
method called filter okay now what this
filter will do is filter will say okay
I want to apply the filter here but give
me a condition so for any particular
value let's say n what you want to do
with this so I can say I can use a
Lambda expression I can say n mod 2
equal to equal zeros I only want a even
number here so this filter and if you
jump to this filter you can see filter
returns a stream so what we are doing is
when we say S1 dot filter it will give
you basically a new stream to work with
let's say S2 again as I mentioned before
S1 is used right so when I say S1 dot
filter your S1 has been used now now you
got a new stream now this S2 basically
will have only the even numbers let me
prove that let me print S2 and let's see
what values you get here so I will say
compile and run you can see we only got
even numbers now say what we are doing
here will have a separate video on this
how Filter Works but the idea is the
filter is filtering the value based on
the even or odd you can specify whatever
logic you want to but at this point I'm
just specifying a logic of a condition
of even right now once you've got this
stream I can create another stream where
I'm doubling the value I can say stream
and I can say integer let's say S3
because it will give you a new stream I
can do that operation on the new stream
which is S2 on S2 basically I'm trying
to double the value right so you can do
that with map in this map for whatever
value you get
uh you can perform some operation on
that at this point I'm just doubling the
value right
as I mentioned you can use any logic at
this point I'm just doubling it
and now let's try to see how this stream
works I'm saying S3 now because you
can't use S2 S2 is done
and if I compile and run you can see we
got double the values we got 8 4 and 12.
so yeah stream provides you this amazing
methods on which you can perform the
operation on one stream it will give you
a new stream you can perform the
operation on the other stream it will
give you a new stream uh in fact you can
also use some methods which will not
give you a stream but a last output
example let's say if I say S3 dot
there's a method called reduce now in
this reduce if you say 0 comma
again I will explain this logic later
what I've did but let's say if I try to
do this if I say C comma e c plus e now
what this values will do it again don't
focus on the logic now just focus on my
reduce this radius will not give me a
new stream this radius will give me a
value of type whatever type you
mentioned with the integer with the
stream which is integer so it will give
me uh into values I can say in result
equal to S3 dot reduce
and instead of using a forage now why we
can't use forage because reduce will
give you a single value which is there
in the result I can simply come back and
I can print the result and I can just
compile this code and run and we can see
we got 24. again let me repeat just
ignore what is happening inside we'll
talk about this in the next video what
is happening inside this idea is stream
makes your work Easy by having this
functions if you have a function like
filter map reduce now this I don't know
if you know about this concept of Big
Data example in this world we are
getting so much of data right now if you
want to use all this data first of all
you have to apply the filter on it there
are some wanted data there are some
unwanted data so you can apply the
filter once you up once you apply the
filter the data which you got you can
transform it something meaningful you
can do that with the help of map and
then you can make a graph out of it
right with the help of something called
reduce and then we were able to print
the result let me just see if that works
compile
no issue run and if you call 24 and this
is
remember we have used a for Loop which
was giving 24. the same thing we have
done with the help of stream
now the beauty is uh you can actually
write everything in one line let me show
you something I will just comment this
entire section and here what I can do is
I can say nums dot I can say stream it
will give me a stream of values on the
same stream I can say dot I can apply a
filter
and this filter can be uh we can very
logic as I mentioned we are going for
even numbers
zero and on the same stream because see
nums dot stream num Sita at least right
it the stream method will give you the
stream on that stream we are applying a
filter again we we will get a new stream
and on the new stream we are applying a
map which is uh n into two and then this
stream will give you a new stream on
which you are applying reduce where we
are saying
0 comma C plus e or C comma e which will
be giving me c plus e
and that's it this radius will give you
one value right and that one value you
can store in a result so this nums dot
stream let me just give a tab here yeah
so this basically nums dot stream will
give you a stream on that stream you are
playing a filter on that stream it we
are playing a map on the stream you are
applying a reduce and then you got one
value at a time and this looks much
better than the for loop I know for the
newcomers this will be difficult but
once you get used to it you'll always
prefer to use stream
okay and uh one of my favorite uh
trainer omenta says venkat subramanyam
says it's not difficult it's just
unfamiliar
okay so uh this is how it works and you
can compare with the for Loop and this
looks much clearer in fact it's much
more readable right on a stream you are
applying a filter on that filter applied
you are applying a map and then you are
reducing now let's try to understand
what is happening here when you talk
about filter what it does when you talk
about map what it does we understood
what it does in the forage it takes the
object of consumer but I'm not sure what
it will do here so what I will do is
just simplify the code I will remove
everything and also let me remove all
this thing so that it will look cool you
know simple code
okay so let's go step by step if we talk
about this filter and if I say okay let
me just go to filter and you can see
filter needs an object you can see
there's a parameter it needs an object
of a predicate now what is predicate I
will just go back here and if I type
indicate here so if I say predicate and
you can see it belongs to a package
java.ital.function and if I click on
predicate here predicate is a interface
which has a method called test it
returns you a Boolean value okay now
based on this Boolean value it will say
okay it can be either true or false if
from a stream you know from a stream
when you apply a filter for a particular
value if this if this is true it will go
ahead otherwise it will stop it's
something like applying a filter on a
river so let's say if you have a reverse
flowing and then you have apply a filter
there and if you want only the pure
water to pass all the garbage will be
stuck somewhere you can do that with the
help of a filter I hope that makes sense
right let's Implement predicate here so
of course pretty ticket needs a type
you'd want to work with and then let me
say this is a
p is equal to and I will say new
predicate now this predicates the
interface so we have to of course Define
it but what method it has so if I go
back and if I say Quick Fix add the
implementation method so the method name
is test
okay remove that so method name is test
and it takes the integer value and based
on some condition which you can specify
you can specify is it true or false so
what I can do here is I can check if
the value t or whatever value you want
to have let's say the value is n naught
I don't like DQ T later let's go with n
so if n is mod and mod 2 is equal to 0
in that case
return true
I can give a tab and I can say
else return false our problem solved
right okay so if it is true if the value
of n is even it is true then if this is
true I will return true or I will turn
false and now what I can do is instead
of this condition here I can put P right
even that should work let's try compile
and run and you can say it was it is
working so basically this filter needs
the object of predicate which specifies
the logic of when to pass the value and
when to stop the value
now if I try to reduce this code don't
you think this condition here itself
returns true
then why to write such a big line we can
actually return
n mod 2 equal to 0 because ultimately we
need a Boolean value right it can be
true or false so we can do this
also the predicate itself is a
functional interface that means we can
use Lambda expression here
so we can remove from here to here we
can remove the entire part we don't even
need to specify the type and we don't
need this curly bracket we can put a
arrow here and then since we only have
one statement you don't even need curly
brackets you don't even need a new key
written keyword we can write everything
in one line and since we have only one
parameter we can remove this one and you
can see the p is equal to this
expression
and whenever you have the expression or
whenever you have P you can write this
expression and this is what we have
earlier right
so now we know how Filter Works let's
see how Map works if I go to map map
needs object of a function okay what
this function is Now function is this
functional interface which takes two
types okay makes sense and there's a
method called apply
okay so what I can do is I can have the
object of map
or not the map the object of function
now this function takes two types one it
is what it accepts and what it returns
and say let's say fun because that is
fun a new function and again this is a
function interface
which has only one method let me just
add that here so this is a method which
we want to override which is apply now
what I want to do whatever value you get
let's say instead of uh and a TV let's
say n whatever you want to do with this
n it will just apply that value so let's
say for this n
what I want to do is I want to return
n into 2.
so whatever value I'm getting I just
want to double it again as I mentioned
logic if anything but I'm doubling it
here
okay makes sense and we also know that
this is a functional interface okay
first of all let me take this fun from
here and put it here so we can say fun
and let's see if that works
I will say compile and run and you can
see we got 24 it works what we can also
do is from here to here this is a
function interface so we can remove this
part
and we can use Lambda here I'll just do
that quickly now we have mastered Lambda
and we have only one statement which is
written so we can remove that
we can remove this curly brackets we can
remove the same integer we can remove
this package
and this is what we got
and now we know wherever you have fun
you can write this and this is what we
had before so we don't even need this
right the same thing can be done for
reduce if I click on reduce you can see
reduce takes two parameters one is the
type and second is the operation okay
now what is this binary operator so
binary operator basically is
it extends by function by function as a
method called apply okay let me simplify
this for you I know this is a lot of
implementation there let me simplify
this thing now when I talk about videos
how do you reduce a value example let's
say if I ask you to add three numbers
let's say one two three how will you add
them now in your mind you are doing this
so if I say one two three and let's say
four also how will you add them of
course you cannot add all the ways at
the same time you add two values at the
same time so first of all you will add
one and two which will give you three
then you will add 3 and 3 which will
give you six and then you will add 6 and
4 which will give you ten right so you
add two values at a time
or maybe if you want to simplify this
you can start with zero so you can say 0
plus 1 is 1 then 1 plus 2 is 3.
okay so you have to start with the
initial value remember when we created
int sum we have assigned the value to of
sum is 0 that is just that is this zero
and every time you will simply add two
values
so if I if I want to add two values can
I say this is c and e
the carry because see this one is a
carry here right this three is a carry
this 6 is a carry this ten is a 10 is
the output of course but this one three
and six they are carry which can be
represented with the help of C
and then we have this e which is the
element right c and e and what you're
doing is you just have to say c plus e
and that's what we have done here the
zero is the initial value what you want
to work with this value
and then the c and e are the two
variables which is going to work with
this thing and the C plus e is the
operation
is that simple okay of course you can do
this with the implementation but I think
you got the point right so stream is
cool right it works with we can apply
multiple functions here in fact let me
show you one more thing
what if I don't want a int result in
between I want a stream itself but I
want this stream to be sorted so I will
say integer
and I will say sorted values
but I don't want to apply reduce because
it just will give you one value I only
want to filter them based on the
condition and then I want to say
sort
that's it the moment you say sorted you
will get a sorted stream
and maybe you can also print this values
directly instead of using a foliage
let's try that compile and run oh it's
you have we have to use for it okay so I
will say sorted
values dot for each
and you can say whatever value you get
just print it okay let's try compile and
run and you can see we got the value
inserted format
so basically we have multiple methods to
work with in fact there is one more
thing what if you want to do the
filtering but with multiple threads
but if I you have only one thread right
what if you want to use multiple threads
in that case there is another function
called parallel stream
which will create multiple threads for
you to make this faster the only thing
is when you say sort parallel stream
doesn't make sense because sorting will
need all the elements together uh so
let's not don't use parallel stream when
you want to sort but yes if you want to
filter parallel stream works okay so
yeah that's how we use stream API and I
hope you got the idea about map filter
and reduce