Java Tutorial for Beginners #20 - Inner Classes

Key Takeaways

hey guys and welcome back to another Java programming tutorial so in today's video we are gonna be going over in our classes now inner classes are pretty pretty easy actually all they are is really just a class inside of another class or inside of a method and I'll show you some examples as we go along but since we already know all about classes and methods and static and whatnot I'm not gonna explain too much of it I'm just gonna kind of show you how we can create instances of inner classes in different ways so I'm gonna start by doing this inside an outer class here that I've already created you can see on the side here I'm just gonna create another class called interpose right now inner class is just gonna simply have one method in it and I'm sure you make this a public void display and in here all I'm going to do is simply just display similar to the screen so we know that we're actually in the right class here okay now let's say this is an inner class okay and what's our error here class at token hmm interesting must have made a mistake somewhere here one second guys oh sorry I put these two brackets here hmm don't know why out of those anyways okay so this is an inner class now outside of this class I'm gonna create another method that's gonna be a part of the outer class okay so this class is actually contained within the outer class meaning that currently since it's private we can only actually access it from within our class so if we want create an instance of this that means we must need a method in our class to do that so in this case I'm gonna say public void inner and in here we're going to take nothing and all we're gonna do is we're gonna create an instance of our inner class and just display okay so we're just gonna say inner class I n equals new in your class like that okay and then all we're gonna do is just call I end display and make sure that this is working okay so now our class is finished we have an inner class and we have this void inner and all that does is create an instance of our inner class and print it to the screen again note that this is private meaning we we access it from within our our class okay so now if I go to my main Java I can run a command so or whatever creating objects that we can see this so first of all what I have to do is create an outer class object so that we can call that inner class so outer class out equals you and an outer class now it is worth noting that I don't have any constructors here meaning that I don't need to give any information to my outer class from my inner class when I first call it and that's why I can just leave these blank brackets okay so now if I want to see my inner class what I have to do is I have to do out dot inner okay so we'll call that method to create the inner class and then run that so let's run quickly here and we can see we get this is an inner class awesome so that's working fine now I'm just gonna make this public now let me show you how we can do this from outside of the class so really now what we need to do is we need to create an instance of outer class and then we need to call the method inner to be able to create the inner class and that's because this was private but now that it's public we should be able to create an instance of it outside of the class so the way that we do that is we still need an instance of outer class because this class is defined with an outer class so we need to first create this so that this is kind of created right so we did that and we have outer class now what I can do is I can say our class dot inner class okay and we just call this one I add equals lower case equal is out which is going to be our instance of outer class dot and then in this case we're gonna strike inner class believe this is correct but I guess we'll see oh I probably need an equal sign and we'll type new new out inner class and let's see what our little red line is create class inner class in package out interesting one second guys okay so that's for the issue I knew it was something like this what we need to do is we need to do a new and then inter class because we're creating a new instance inside of this right of outer class of inner class okay so now what we've done is we've created this i n which is an object which is a new inner class so now we can simply use I n which is an instance of inner class right to display so now we can do a and display okay so if we run this see this is an inner class and that is working fine so those are two ways you can go to access the inner class now right now you might be like kay well why the heck would I do this because now it's just like a ton more lines well there's many times where you don't really care about like this instance and you just want an instance of the object inside of it so in that case this would make more sense to do and obviously you would most likely have more methods than just one that you're gonna be using okay all right so now that we have that I guess let's show creating this kind of inner class stuff so I'm going to delete this inside of a method so we can actually create these inside of methods which are really useful because sometimes within the method we want to use a class and we don't want to have to define like a new file for another class okay so we have this public void inner so I guess let's just work with this right now you know even leave in a class right now I'm gonna show you how this works so all I can do in here anything and say I want you do public you private in this case I'm just gonna say I'm gonna just say class let's see in class in a class and then here yes that works fine we're just gonna redefine display so just say public void display and now that I think of it I probably could have just copied out my other code but whatever get some practice typing println and then in here again well this should probably be a t we will just type inner class okay so this is going to work perfectly fine whenever we call this void inner then we have this class inner class we're gonna create an instance of it and we're going to display it so if I run this I guess wow I really should just kept all that code that's fine why is this not giving you the autocrat outer class out because new and out of class and brackets and then in this case we'll simply just call out dot inner ok so now we can see what should happen is again we should print inner class so there we go and we get inner class now pretty much you can do this like wherever you want the reason I'm not saying this is public or private is just because like it's already within this void so to use it we're gonna have to call this void so there's no really there's not really a point in putting like private or public but again like if you wanted to type public class inner class or oh actually saying you can't do that so I guess I was right the first time so since it's inside of this void you're only gonna be able to use when we call this so there's no route point and really giving it like a public or private method or class name sorry because in here we can still do public and private methods because we'll outside of the class we might be using those methods right so you can see obviously since I'm creating this instance inside of the the void so inside of you know and if I tried to do that outside of it it wouldn't work because this class is only defined when we call the inner method okay so I think that's kind of been it for inner methods there are like anonymous inner methods and some few a few like other cool things you can do with it but I don't find them particularly useful so I'm not going to teach them here especially in like a beginners tutorial but if you guys are interested in learning about them I will leave a link in the description just for any of you guys that are curious and as always if you enjoyed the video please make sure you leave a like and subscribe and I will see you again in another one [Music]