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OK let's just go ahead and write some code on most of the stuff we have learned in the previous lesson

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about interfaces.

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OK so let's get started on let's create a new interface called a.

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So let's just use the same names we have used in the previous lesson.

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Let's add two methods for one.

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So these are two abstract methods and recall that we can omit the key words the modifiers public and

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abstract because they are implicit.

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OK so they are included by default.

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So let's just let me just say that.

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And at this fine and we will say we're in this new folder called interface which is created within com

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semantics Square.

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OK.

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OK.

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So let me just say right here you are Java.

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Now let's create a subclass.

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Let's implement this interface.

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But let's keep the class as an abstract class so it has to be abstract class it's name it as abstract

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.

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And it implements a

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out of the two methods.

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Let's just implement one off them.

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So let me just copy this code and here we are providing an implementation for the Barmouth.

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And so for the Fruma Third we are not providing any implementation in this abstract class since it's

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an abstract class.

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It need not provide implementation for any of the inherited abstract methods but here we are just providing

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for one of them.

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So the missive does

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not look miscreate as such another subclass of this class abstract it and let's call it does x.

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So this is a concrete class

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so it extends abstract a under-the implements a.

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It need not implement it because it's actually extruding abstract and abstractly intent in clemency

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but let's just leave it like this.

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Let's just say it does not have any body.

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And let's not have any code in the body.

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Now we also have a test class called desk.

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And here it is the main method.

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You now you can ignore this method get round and here we are instantiating the interface A which was

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a compilation error because interfaces cannot be instantiated.

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Recall that an interface can only be used as a reference type but not as an object.

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So the compilers and ADO do Senator.

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This is abstract because A is an interface and it cannot be instantiated.

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So let me change this to hex.

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So we are instantiating the concrete class X and we are invoking the two methods foo unbar and let's

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combine this now.

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Now it says X is not abstract which is true because X's concrete does not override the abstract motard

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.

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Right because we have not yet provided an implementation for the abstract matter with us for the abstract

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method bar we are inheriting a we are getting the free implementation for them both of them.

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Abstract.

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Because I have struck it has implemented bar and X's inheriting it so that's good enough.

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So for bar we have an implementation for bugs not for food.

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So let's provide that implementation.

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So let me just copy this.

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Change it to who make this class hag's and within X we are printing.

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For now everything should be fine.

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You go it's printing foo which is in Class X underspending bar motard the the message from bar which

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is an abstract.

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So the bottom of that definition was provided here.

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Even if this was if it was not implementing a hundred just an independent class an X is still extending

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abstract A.

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Even in this case it would still it could do X doesn't have to define but it would still use the bar

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defined in abstract so everything would work as it is working now.

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So we discuss this and the lesson in the previous lesson.

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So let me just compile and run it so it works the way it was working.

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So let me just say re-inserted.

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Now let's look at the diamond problem.

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We know that the diamond problem is not there in Java.

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So we already discussed it.

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And so we have a new interface called Beat and it also has this declaration the abstract method fool

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.

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He also has abstract motard food and let's just from X let's implement B.

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So we are doing implementing multiple interfaces here on both the interface and have the same method

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.

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And we there is no Diamon problem here because we are just inheriting method declaration but that actually

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meant the definition is that is provided here in the class X.

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So there is no chance of a diamond problem.

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So let me recompile this.

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I mean exactly.

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Everything is fine.

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No let's just go ahead and test the constants.

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Interface can have a constant.

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So what are we discussed about constants.

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Let's just go ahead and do it.

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So in a I mean just I add

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this variable called cloud.

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So implicitly It is actually a static final one.

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So actually let me just remove this.

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Let's compile this.

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So here it gives a compilation error.

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It says that Val in origin gives a compilation error.

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That's because the value variable is a static final variable.

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Iron is started quite and has to be initialized and that did not happen here.

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So let's go back to a and let's initialize it do you find.

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And let's go into this.

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X let me print that value

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.

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So now it's printing the value.

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So that's so we need we have to initialize it for sure if it is a variable we need to initialize it

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because it's static final and final values have to be initialized.

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Now let's do just the name clashing of the variables.

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If you recall we discussed this.

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So indeed our job also.

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To declare the same variable.

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But let's initialize it to a different value 42 and existing it accessing it.

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But we have to.

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It's you know we cannot simply compile javac does client because job does cry and we would use would

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instantiate this X introduced or entia instantiate x.

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But then I mean it really not recompile X because there is no change in x x remains the same.

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It's just that our only be has been changed.

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OK.

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So.

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So then we just compile it as a client.

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It would see if there is any change in x and x is not changed because it's it because we haven't made

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any change here.

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So we're just used up all classify loff x.

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And so we won't see any issue there.

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So there is no point just compiling test line.

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What we need to compile is X.

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OK.

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You see when we when we compile X then it was in our Edwar checking if there was any change in a or

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b or abstract a and b b we introduce this new statement.

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So a recombines beat and then it gave us this compilation error as a reference to what is ambiguous

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because we we now have rightly defined in both A and B and it has since it has the same name.

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It is ambiguous so we need to qualify it.

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So if you recall we need to qualify it like this so let's say we are accessing B.

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So now we can do this and it works fine.

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Let's recompile.

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Slide.

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That's your own test line and it prints 42 now.

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So because it we are accessing the 1 and B.

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So that's named plashing and let's instead of giving a literal 42 Let's actually assign the value 42

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by making him a method call.

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So we introduce this method called get around and test blind and all it does is simply write down the

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value 42.

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So it's just that the this is a different way of initializing it.

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And instead of later we are using a method call.

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OK so let me just go ahead and recompile just glide mean x.

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Let me recompile X

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and ask Klein which is not new direction and so it brings the same value.

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So so that's a different way of initializing a variable and interface.

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But normally you would just pro-white literally wouldn't be doing this kind of any initialization at

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least I have never seen it.

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So that's about a variable initialization and that's about it.

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And as simple exercise that I want to give you as extruding an interface so let's say I want you to

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do that.

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So just create a new interface.

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We have two interfaces.

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A and B.

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So go ahead and create a new interface called C and C should extend it.

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OK I can just add a new abstract method called foobar.

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So earlier we had foo on bottle separate but that's just go ahead and add a new method called foobar

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.

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And so that's an interface extending another interface.

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So C interface C is extending a notch adding a new metric or foobar and from X just implement see just

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do something like this and provide an implementation for foobar and all you can do is just simply print

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out how and edit print statement column X uncolored foobar.

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So just provide the method definition foobar within X so that's all I want you to do.

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And you can find a code hundred code and resources section and it will also include this new interface

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and that's about it.

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Farnol