Java Programming Tutorial - 57 - Overriding Rules Video Lecture - Java

what is going on people welcome to your
57th java tutorial and this tutorial is
going to be not a lot of coding actually
it's going to be pretty much clearing up
a whole bunch of concepts dealing with
polymorphism and trust me you're going
to have a huge a better understanding of
polymorphism by the end of this tutorial
so I just want to go over um overriding
a method or real quick in something I
didn't tell you about
we built this superclass called food in
two subclasses called tuna and potpie we
called a method and food and we call to
eat and we overrode that method in tuna
and potpie
each of these had a method that overrode
it so one thing I didn't tell you about
overriding a method anytime
you override a method you must take the
same arguments as in the superclass
method so since this e argument didn't
have any arguments in it it doesn't have
like integer this tuna can have like
integer argument for this and this
papaya can't do the same whenever you
put an argument in here this is called
overloading and that's totally different
but again if the food if the main eat
method doesn't take any arguments which
it doesn't tuna and pop pi can't take
any either and also in that same path it
has to return the same thing too so for
example if you returned an integer in
here it would have to excuse me if we
return an integer in the superclass it
would have to return an integer in the
subclass as well and if you're saying
all right why do I have to do this why
do I have to not take any arguments and
return the same stuff if I'm overriding
it and in essence doing a whole nother
method well it's so that you can have
consistency and that is just so anytime
you can call the eat method in any of
your other scripts then it pretty much
guarantees that you can use any of the
sub classes as well so if all of these
methods take the same arguments and
return the same things then they are
pretty much interchangeable and that
allows you to use a subclass and
substitution anywhere you can use a
superclass so that pretty much then you
know what to expect and another thing I
want to talk about anytime you override
a method so for example we have this
food method in our superclass and we
overrode it with tuna we cannot change
the scope of this so for example this
food is public right here we can't put
private void II see we're getting an
error already
this changes the visibility of it and
why would you override it with a private
anyway so you know you just don't want
to do that and as I talked about
overloaded method is not the same as
override
well overloaded method is if you hear
anybody talking about this an overloaded
method is a method with the same name
but it has different arguments so for
example we can do this in I and not get
an error but this is a whole nother
complete method so then over so if
someone calls eat with a single argument
then this method is called but for now I
just want to tell you guys that
overloaded and overridden are two
totally different things so don't get
them confused so now that we got that
out of the way in in essence I pretty
much just want to tell you that whenever
you override a method you have to take
the same arguments and same return types
there I said I just said it in like
three minutes the other time so let's go
back to our Fatih class right here and
let me refresh your memories we know we
can do something like reference have a
tuna reference and set tuna object equal
to like new tuna and as you know this is
the tuna reference right here and this
is the tuna object and we can do this
since tuna is a tuna and we can also do
something like food food object equals
new tuna and we can do this because tuna
is a food and those are the things we
learn in less orioles but what have we
not seen so far what we haven't seen so
far is food food object equals new
food huh what about that well this is a
problem for many reasons tuna and Popeye
we wouldn't have a problem with and this
is because when we put variables in here
like color shape tuna has a color tuna
has a shape Popeye has a color papaya
has a shape food is too general it
doesn't really have a color it says what
color is food I don't know what shape is
food I don't know and if you say alright
I can eat a tuna
I can eat a pot pie but I can't eat a
food food is really too general and I
know that there might be some exceptions
to this but for the sake of programming
there are some classes that are just too
general that you don't want to create
objects on in this food class is one
example so if we had food class we want
to want to give it any variables like
color or shape because food in general
doesn't really have a color or shape so
all right that's nice and all I kind of
knew that already Bucky so why are you
telling me this I mean I'm not giving
you guys a tutorial to tell you guys
that tuna has a color but what I am
giving you guys teaching you guys it
says in even though we can't create food
objects like right here
we need this food class still for
inheritance and polymorphism but when we
create this class we want to make sure
other programmers can't create food
objects either so how can we make this
food class right here and and how can we
kind of bulletproof it to make sure that
no one creates an object and they only
use this class for inheritance and
polymorphism and stuff like that well
luckily the cool people who invented
Java gave us this keyword and it's
called abstract and how you make a class
abstract this type a be STR a CT
abstract right before the class and what
this does is mean all right you can use
this class or right here the class of
food but you can't create any object
sermon oh yeah one bet look at this food
food object equals new food object right
there oh I did oh look I got an error
I guess bucket is right I can't
instantiate the type food and that
pretty much means you can't create an
object anymore so if we take that
abstract away look at this the air it
goes away and now we can create an
object so again what abstract means is
that you can't create an object from
that class but you can use that class
from for things such as inheritance and
polymorphism and stuff like that and
that is so when you have a broad class
that you only want to use for those kind
of things then it kind of bulletproof
your programming and in the next
tutorial we're going to be going over
the two different types of classes
abstract we went over in concrete I'm
going to be showing you guys an example
of why it is useful and also what
abstract methods are so this next couple
tutorials is more of general ideas and
then we're going to be building programs
to use these ideas and put them to use
use them and put them to use did I say
that right my good enough but thank you
guys for watching hopefully you guys
understand that um anytime we override a
method you need to take the same
arguments and also the beginning of what
an abstract method in excuse me extract
class is so again thank you guys for
watching please check out my next
tutorial and I will see you next time
oh by the way don't forget subscribe