Java Programming Tutorial - 49 - Inheritance Video Lecture | Java Programming Fundamentals: For Beginners - Back-End Programming

so guys welcome to your 49th Java
tutorial and in this is order I'm going
to be talking about inheritance
now what inheritance is is pretty much
inheriting stuff from another class so
why is this useful well say we have two
classes right here tuna and potpie and
in the tuna class we have a method like
public void we'll just name it eat and
let's say armed in this method all it
does is go system.out.print line and
then it just print something like I am
the eat method and safe we had a bunch
of different little food classes and
every single food class had this method
so tuna had it and potpie had it and say
we had a bunch of other ones like
chicken liver ham they all had the same
exact eat method so then your boss comes
in and tells you all right you know when
you wrote the eat method say I'm the eat
method
well we actually want you to say I am
the e methods with s so now you got to
go in every single different clef class
and change that one method and add an S
on the end and you're saying alright
I wish instead of having all these
copies that I would have to maintain if
I could just have one single copy so
that's what exactly inheritance is
instead of having all these copies and
different classes that you have to
maintain you can only have one single
copy that you have to maintain in each
of these classes can inherit that so
let's go ahead and copy this and since
tuna and Popeye or both foods
I made this new food class right here
and what this food class is going to do
is it's going to store all the things
that tuna and Popeye have in common and
right now they have this eat method in
common so we can go ahead and get rid of
this method right here and
get rid of this method in here and
instead of having all these separate
methods in all these classes we only
have to maintain this one method in the
food class so how exactly does this work
and how can we only have one method to
kind of take care of well this is what
inheritance is instead of having a bunch
of different methods what this tuna
class and Popeye class can do is it
inherits everything the variables and
methods from this main food class and
whenever we do this the kind of methods
that inherit the stuff those are called
the subclasses and this stuff that they
or the class that they inherit from is
called the superclass so again these two
tuna and Popeye classes are going to
inherit all the stuff that's in the food
class and the food class is called the
superclass in the tuna and Popeye class
are called the sub classes so how
exactly do we inherit everything well
instead of saying inherit from what Java
said is it gives it a new keyword name
extends ext BND s and whenever you write
extends this means inherit from so say
public class Popeye extends food this
means all right in this class potpie
we're going to in hair everything from
food so we're going to inherit any
variable that would be in hair in all
the methods so let's go ahead and do
that same thing from tuna so public
class tuna this class ext inds it
extends food so now anything that's in
food is inside Popeye and tuna even
though we can't see it that's what we
mean so let's go ahead and let me show
you guys that right now so say we go or
whatever your main method is right here
let's go ahead and make a object so I'm
going to make my tuna tuna object and
let's just go up ahead and put new tuna
let's just go ahead and make the same
thing with top pie
so pop pie
PAH object would be JCT and I'll figure
it out eventually new popeye so now we
have a toon object and a potpie object
sure I didn't mess anything up
so now even though we have no methods in
here they inherited all the methods from
food so we would use those methods just
like we would anyone else so this method
is called eat don't remember and it's in
pot pie and tuna even though you can't
see it so let's go ahead and put tuna
object eat and pop pie or what's called
pot object eat and see what happens
and we're getting a error right here oh
we forgot to equal sign there we go and
now when you run this we see I am the
eat methods and this one came from tuna
and this one came from PAH object so
that's how you can have you can hare
inherit all the methods from another
class using the extends keyword but what
if you're saying alright you know I have
a bunch of different foods and I know we
only have two foods right now this is
just them trait but I'm saying alright I
have a bunch of different foods like
tuna potpie chicken liver but I have
this one class called tuna and I want to
inherit all the stuff from food but I
want to change this one method right
here well what you can do is override
certain methods and in order to override
certain methods you just put the method
into the class the subclass and you
recreate it so then if you say all right
I am the new method of tuna so make sure
you spell a couple things wrong there
and now whenever you override something
you inherit everything from the food
class but the methods that you recreate
they're going to override or overpower
the methods that you inherited so now if
we go ahead and run this we see this
let me get it up for you there we go
I am the new method of tuna and this is
the method that we overrode and again
the it's the easiest thing in the world
whenever you want to override something
all you have to do is pretty much just
create it again
and then you don't have to worry about
you know well it's pretty much as simple
as that I can't explain it any better
but that's how you override something in
PI objects we didn't override that
method so that's why I got the default
food method and then the last thing or
the last couple things I want to talk
about real quick if say tuna extends pot
pie and pot pie extends food then tuna
inherits all the stuff from pot pie and
food it's like a little hierarchy so
let's go ahead and delete this and now
when tuna extends Popeye and inherits
all the stuff from pot pie and food and
the last thing I want to take note of is
that only let's go ahead and get rid of
one of these objects let's go ahead and
get rid of the pot object only the
public methods can be inherited let me
see how much time I got left
two minutes only public methods can be
inherited so if you have a private
method in the superclass again the
superclass is the one that the subclass
inherits from and we want to change that
to food so right now tuna is inheriting
all the stuff from food but food has
this method in here that's private what
private means is all right you can't
inherit this from me in order to inherit
it it needs to be public like we did
before but when we put private like this
and try to run this right here we get a
little error right here and it says the
method eat is not visible so whenever we
try to run it I'll show you the syntax
error down here and then pretty much
this is saying all right this isn't
visible because food has a private thing
that you tried to inherit in news and
you can't it's
private it's not public so that's your
real quick tutorial on inheritance and
pretty much anytime you want to inherit
crap from another class just write
extends and extends is this a real fancy
word for tuna inherits from food or tuna
inherits all the methods and variables
from food and again well that's it for
this tutorial I already filled your
brain with enough so that's your real
quick tutorial on inheritance I hope I
made it simple I hope you guys can
understand so thank you guys for
watching and I will see you next
tutorial