overriding not liked by the compiler

Question

I use jdk 6.

I have an interface:

    public interface DisplayValueListener<P>  {

         ...

         void setDisplayValue(P value, String reprValue);
    }

I have an abstract class named Widget that implements DisplayValueListener and is declared like this:

    public abstract class Widget<P> implements DisplayValueListener<P> {

        ...

        @Override
        public void setDisplayValue(final Object value, final String reprValue) {
            ...
        }
    }

I also have another abstract class that extends Widget like this:

    public abstract class CameraWidget extends Widget<Void> {

        ...

        @Override
        public void setDisplayValue(final Void value, final String reprValue) {
        }
    }

This is the message that I get from the compiler in NetBeans:

name clash: setDisplayValue(Void,String) in CameraWidget overrides a method whose erasure is the same as another method, yet neither overrides the other first method: setDisplayValue(Object,String) in Widget second method: setDisplayValue(P,String) in DisplayValueListener where P is a type-variable: P extends Object declared in interface DisplayValueListener

Can anyone tell me what is the problem and why the compiler in Eclipse (same jdk 6) is happy with this?

Answer 1

You need to use the generic parameter P in class Widget when you override the method:

 @Override
 public void setDisplayValue(final P value, final String reprValue) {
     ...
 }

Eclipse uses an own Java compiler and not javac and sometimes these two compilers interpret the Java spec differently.