difference between implements and extends

> Hi,

> i am new to java. can any one help me to

> lp me to understand the difference between implement

> and extend

>

> Thanks in advance

Hope you are'nt finding your replies confusing!

Anyway I'll have a go trying to avoid jargon but it's difficult!

When you implement an interface you promise that your class will have the methods that are required for that interface. They must each have the right name and the right parameters too. The catch is that you must write them!

When you extend a class you don't promise to write any new methods although you can and normally you would. Even when you add methods you can call them anything you want unless you are replacing one which you inherited.

Let me know if you got it now.

Gargoylea at 2007-7-16 13:28:24 >

> I'll have one more go changing the words slightly.

>

> When you extend an interface you MUST write at least

> one method.

>

> When you extend a class you MAY not have to write any

> methods although you probably will want to.

>

> Agreement?

Nope.

Only an interface can extend an interface, and in that case you don't implement any methods.

I assume you meant when you implement an interface though. But again, no: public interface Foo {}

public class Bar implements Foo {

// I don't have to write any methods

}

Really, there's no difference in the underlying meaning of the words. As UJ says, they could both just be replaced by, for example, "inherits." All they really do is emphasize or highlight what's already determined by the types of the two participants in the relationship.

targaryena at 2007-7-16 13:28:24 >

> public class Bar implements Foo {

>// I don't have to write any methods

> } [/code]

Also: public interface Foo {

public void baz();

}

public abstract class Bar implements Foo {

// I don't have to write any methods

}

targaryena at 2007-7-16 13:28:24 >

> > A class may implement many intefaces but may

> extend

> > only one class.

>

> While that's true, it's not really a significant

> difference between implements and extends.

>

> As already mentioned, we could replace both with

> inherits, and then we'd just say that a class

> may inherit from many interfaces but only from one

> other class.

>

> Besides which, you can list multiple types

> after "extends" even in current Java.

OK

Gargoylea at 2007-7-20 18:56:31 >