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javaandroidinheritanceinterfaceimplements

Cyclic inheritance and interfaces - class A can't implement class B interface while class B implements A interface


I have:

public class A implements BListener {
    public interface AListener {}
}

public class B implements AListener {
    public interface BListener {}
}

So, if I understand correctly the cyclic inheritance happens because:

The compiler goes to A and says "hey, A implements BListener, let's go find BListener!"

Then when it tries to find BListener, it eventually gets to B, which it says:

"Hey, BListener, needed for A is inside B! BUT WAIT! B needs AListener! Let's go find AListener!"

And then it gets to A, repeat. Did I get this right?

By the way, this compilation error happened to me on Android development.


Solution

  • It may help to draw it out.

                  >A 
    is part of  /     \    inherits
                       V             
       AListener        BListener
               ^
      inherits  \     /    is part of 
                   B<
    

    A lovely circle. You can't create one of them without the others already existing.

    Is the compiler a squirrel with ADHD high on coffee chasing it's own tail?

    Nope because a the squirrel would not stop (until the caffeine ran out). The compiler looks for this and then gives up.

    Note: Eclipse has a bug which allows this setup.