Nested Interface?? in SCJP 1.4

[Micheal John]

interface t1{
 
public void aMethod();
 
interface t2{
public void bMethod();
}
 
class NestedClass{
public void cMethod(){
System.out.println("in cMethid");
}
 
interface t3{
public void dMethod();
}
}

}
 
class NestedInterface implements t1{
public static void main(String args[]){

}
 
public void aMethod(){
System.out.println("IOverridden aMethod()");
}
 
}

How can we implement the nested interface? What it's use?
How can we extend an nested class that is declared inside an interface? what it's use?
I have implemented interface t1 in class NestedInterface,but not implement the methods of nested interface t2..how it compile and run?
[ December 05, 2006: Message edited by: Micheal John ]

[Barry Gaunt]

You asked for it:

public class LooksFunny extends t1.NestedClass
    implements t1, t1.t2, t1.NestedClass.t3
{
    public void aMethod() {
    }
    public void bMethod() {
    }
    public void cMethod() {
    }
    public void dMethod() {
    }
 
}

[Burkhard Hassel]

Micheal John posted December 05, 2006 05:57 AM

How can we implement the nested interface? What it's use?

use?


By the way, there is no need to override methodC

Bu.

[Jim Yingst]

It is always possible to create bizzarre, convoluted code and then ask "what's it's use"? However it's not necessarily worthwhile to anyone. To see a realistic example of when a nested interface can be used, look at the Map interface, and the Map.Entry nested within it. The only purpose for this Entry interface is to be used as part of a Map, so the authors thought it made sense to present the interface as part of the Map interface. They certainly could have simply used a single separate Entry interface instead, but they chose not to. The idea is that when two classes or interfaces strongly related, we try to present them very close to each other (e.g. one nested in another).

The other way to look at this is, if they had said that you couldn't define an interface nested within a class or interface, there would probably be people writing strange code and asking "why not"? This is one of those language features that could have been omitted, as we never really need it - but there also doesn't seem to be a compelling reason to ban it, either. So you can always find people wanting to know "why" or "why not", and sometimes it really doesn't matter much either way. Maybe the engineers sometimes just tossed a coin to decide whether to allow some of these language features.