about inner classes

[Rajesh Tarigopula]

Hi,
we can declare an inner class as abstract or final. Then where and how we can impliment the abstract methods of an inner class and what is the meading of making an inner class final.

Similary if we declare an inner class as method local with abstract or final
then where and how we can impliment the abstract methods of an inner class and what is the meading of making an method inner class final.

how can we inherit an inner class if it is not final.

Thanks & Regards
Rajesh

[Tony Morris]

Yes an inner class can be abstract or final (but not both).
A final inner class simply cannot be inherited from.
An abstract inner class cannot be instantiated and typically contains one or more inner classes (less common that final inner classes in my experience).

Hope this helps.

[Jeroen Wenting]

you could do something like this:

public class OuterClass
{
  abstract class AbstractInnerClass
  {
    abstract void doSomething();
  }
  class ConcreteInnerClass extends AbstractInnerClass
  {
    void doSomething() {
      System.out.println("Hello World");
  }
}

how useful that is remains to be seen
Probably you could also declare the outer class as abstract and defer implementation of the abstract inner class to childclasses of the outer class like this: (I haven't tried any of this, mind)

abstract class AbstractOuterClass{  
    abstract class AbstractInnerClass  {    
       abstract void doSomething();  
    }  
}
public class ConcreteOuterClass extends AbstractOuterClass{  
    class ConcreteInnerClass extends AbstractInnerClass  {   
       void doSomething() {
        System.out.println("Hello World");
       }  
    }
}

which seems more useful by far.

P.S. corrected code so it now compiles (doh) and indeed it compiles.

[ October 20, 2004: Message edited by: Jeroen Wenting ]
[ October 20, 2004: Message edited by: Jeroen Wenting ]