Java Programming Tutorial - 14 - Using Multiple Classes Video Lecture | Java Programming Fundamentals: For Beginners - Back-End Programming

so guys is Bucky welcome to your 14th
jump tutorial and this story I'm going
to teach you guys how to use multiple
classes now so far I've taught you guys
how to build everything in one simple
class such as this but usually in a like
99% in time if you're working for like a
company or building a bigger application
or program any time you want to build
something that's bigger than something
really simple you need to know how to
use more classes or multiple classes and
then you can use those all in your main
class or let me just show you guys how
this works so to get another class
hopefully you're using Eclipse go ahead
over to your source file right click it
and go to new class now go ahead and
give this a name like tuna or something
like that and you'll see why this is
useful later on so now we have as you
can see from our tabs we move this over
we have apples class and the tuna class
now it started out writing our tuna
class for us it says public class tuna
now anytime you see public it pretty
much means that this class is going to
be available to the public or anything
else can use it so let's go ahead and
now that we have a class before I show
you guys how to use it let me show go
ahead and write a little method in here
now let's go ahead and write a simple
method in this other new tuna class that
we just built type public void and again
public means anyone can use it
void means that it's going to do
something this method is going to do
something but it's not going to return
any data so then go a name ahead and
name your method I'm going to name my
simple message since I'm just going to
be printing out a simple message and
that message is going to be
system.out.print line and let's go ahead
and add something like
this is another class so now we have
another class and this is called public
class tuna and our method is public
avoid and don't forget to put a simple
message in here somewhere you can put
anything you want and now if you see if
we go ahead and try to run this try to
run it okay
nothing happens right here and this is
because I told you guys anytime you run
a Java program it looks for the first
thing that says main and runs it from
there as you can see you don't have main
anywhere in here so it doesn't really
know where to look first so in order to
use this class we need to go ahead and
use it in main so here is our main
function or method right here and it's
in the main class one remember this is
the main one that we use before it the
other one is the new one that we built
so let me give you guys a little
background whenever you use a method in
another class say we want to use this
method simple message and it's in the
tuna class what we need to do is go
ahead and create an object of that class
so the first thing we do is put the
class name which is tuna next we need an
object name and you can name this
anything you want I'm going to name my
tuna object and what this object is
gonna allow you to do is use all the
stuff that's in this class again if you
didn't create an object and you had like
five classes and what I know what class
you're talking about so that's why we
need an object so we're saying are a we
have this object because we want to use
something from the tuna class and of
course you need to set it equal to
something and you always said equal to
new in the class name with empty
parameters for now so now we have an
object called tuna object that we can
use to get anything we want from this
tuna class that we just build
so let's go ahead and use it what you do
to use this is go ahead and put the
object name which is tuna object spell
it right
tuna object and then after the object
name what you do is add a dot separator
and after that dot separator
you use the method name so what was our
method name uhm simple message so simple
message empty parameters and let me tell
you guys why you use a dot separator in
the method name because this class even
though we built one method right here it
can have as many methods as one since it
can have a method name simple message
simple message to dimple message um
bacon and cheese but it says all right
we have this object we want to use in
tuna class and we want to use this
method so if there are other methods we
want to use this one so that is how you
use a specific method in a specific
class by creating a class or excuse me
an object of that class so let's go
ahead and unlike before when we run this
program we get the message that we just
built this is another class and so this
is how you can use different classes in
your main program or your main method so
this is a way that if you own like a
software company you can say alright
Tommy we need you to build one class to
do this John we need to build another
class to do this Stephanie we needed to
build another class to do this and then
you is the head programmer would put all
those classes together and it's just a
way that different programmers can
combined all of their work without
having to work on the same file so this
makes it a lot easier again that's how
you use a different class such as this
an outside class and call it into your
main method or function so that's your a
quick tutorial on using multiple classes
follow this tutorial exactly and play
around with it and soon enough there
will be expert at it so again thank you
guys for watching make sure to subscribe
to my channel and make sure to check out
my next tutorial