interface extends?

[abalfazl hossein]

public interface ActionListener extends EventListener {

  public void actionPerformed(ActionEvent e);

}

How an interface could use inheritance?

[Winston Gutkowski]

abalfazl hossein wrote:How an interface could use inheritance?

Simple: exactly as you see. The interface defined inherits all the methods defined by the one it extends - unfortunately, EventListener doesn't have any; otherwise you'd soon discover the "inheritance" if you tried to define a class that doesn't implement all the methods in the "parent" interface.

Winston

[Seetharaman Venkatasamy]

If you surprised why one interface extends another :
designing a perfect specification is difficult and most of the time may change in future.
so you cant add any methods in existing interface, since it breaks existing implementation.
so we need to give VersionnewSpecification(which also includes existing).

[abalfazl hossein]

Winston Gutkowski wrote:

abalfazl hossein wrote:How an interface could use inheritance?

Simple: exactly as you see. The interface defined inherits all the methods defined by the one it extends - unfortunately, EventListener doesn't have any; otherwise you'd soon discover the "inheritance" if you tried to define a class that doesn't implement all the methods in the "parent" interface.

Winston

don't get the point at all.May you give me a simple example how an interface can use inheritance?

[Henry Wong]

In my opinion, the "extends" keyword is overloaded here -- as what classes do to "extend" another class, and what interfaces do to "extend" another interface aren't exactly the same thing. The Java designers probably did it to avoid another keyword.

On the other hand, an instance of ActionListener IS-A EventListener, so maybe it wasn't a bad choice to reuse that keyword.

Henry

[abalfazl hossein]

Henry Wong wrote:In my opinion, the "extends" keyword is overloaded here -- as what classes do to "extend" another class, and what interfaces do to "extend" another interface aren't exactly the same thing. The Java designers probably did it to avoid another keyword.

On the other hand, an instance of ActionListener IS-A EventListener, so maybe it wasn't a bad choice to reuse that keyword.

Henry

I appreciate Sir,But May you do a favor and give me example about how an interface use inheritance, just conscious

[Junilu Lacar]

abalfazl hossein wrote:just conscious

Then wake up and pay attention, man! (just kidding) -- I think you meant "just curious"

[abalfazl hossein]

Junilu Lacar wrote:

abalfazl hossein wrote:just conscious

Then wake up and pay attention, man! (just kidding) -- I think you meant "just curious"

Take it easy buddy!

[Winston Gutkowski]

abalfazl hossein wrote:don't get the point at all.May you give me a simple example how an interface can use inheritance?

I think you'd be far better off looking at the tutorials, but here goes:

public interface Parent {
   public void foo();
}

public interface Child extends Parent {
   public void bar();
}

public final class ChildClass implements Child {
   // ???
}

What methods do you think ChildClass need to implement?

Winston

[abalfazl hossein]

Winston Gutkowski wrote:

abalfazl hossein wrote:don't get the point at all.May you give me a simple example how an interface can use inheritance?

I think you'd be far better off looking at the tutorials, but here goes:

public interface Parent {
   public void foo();
}

public interface Child extends Parent {
   public void bar();
}

public final class ChildClass implements Child {
   // ???
}

What methods do you think ChildClass need to implement?

Winston

It can implements foo and bar, Right?

[Winston Gutkowski]

abalfazl hossein wrote:It can implements foo and bar, Right?

No, it MUST implement foo() and bar(); and the reason is that Child inherits the foo() method from Parent.

Really abalfazi, you must not guess; you need to read the relevant books or tutorials and understand.

And believe me, firing off vague questions on forums like this is not the way to do it - or at least it's going to be a LOT slower than doing what I suggested.

Winston

[Junilu Lacar]

abalfazl hossein wrote:Take it easy buddy!

Sorry, didn't mean to offend you. I did add that I was just kidding, meaning I was just joking around. Again, no offense intended, just trying to help you with the right term that you wanted to use.

[abalfazl hossein]

Junilu Lacar wrote:

abalfazl hossein wrote:Take it easy buddy!

Sorry, didn't mean to offend you. I did add that I was just kidding, meaning I was just joking around. Again, no offense intended, just trying to help you with the right term that you wanted to use.

Dear Junilu! It doesn't offend me at all!

You are a very good person,Thank you friend! You guide me and I appreciate!!

[Junilu Lacar]

Well then all's well that ends well. Winston is right though, you should read the tutorials. Here's the google search that you can start with: java interface extends another interface Good luck!

[abalfazl hossein]

Let's talk about this method:

public void actionPerformed(ActionEvent e);

What does ActionEvent and "e" do?

[Winston Gutkowski]

abalfazl hossein wrote:Let's talk about this method:
...
What does ActionEvent and "e" do?

Doesn't look like you've listened to anything I said: This is NOT the way to learn Java.

ShowSomeEffort (←click) and read the API documentation or look at the tutorials.

If, after doing that, you still have problems, come back with a question about the specific issue that is causing you problems.

Winston

[abalfazl hossein]

I read this tutorial:


http://www.javamex.com/tutorials/swing/events_listeners.shtml

[Winston Gutkowski]

abalfazl hossein wrote:I read this tutorial:
http://www.javamex.com/tutorials/swing/events_listeners.shtml

So, did it help? I'm not familiar with javamex, but in general I find the Sun/Oracle tutorials (the ones I suggested) very good.
I believe they're also available in multiple languages.

However, that's less important than the process you go through to learn. Simply asking "what's this?" or "why this?" especially if you haven't read any background material is a sure path to:
(a) frustration
(b) annoying the people you're trying to get information from

Winston