Using Java generics in an interface to enforce implementation of a method with the implementing type as a parameter

Question

I have an interface like this:

public interface DataObject {
    ...
    public void copyFrom(DataObject source);
    ...
}

And a class that implements it:

public class DataObjectImpl implements DataObject {
    ...
    @Override
    public void copyFrom(final DataObject source) {...}

    public void copyFrom(final DataObjectImpl source) {...}
    ...
}

Is there any way that I can enforce the implementation of a "public void copyFrom(DataObjectImpl source)" method in the DataObject interface, using generics or otherwise?

Answer 1

If you just need to handle copyFrom differently if the DataObject it's given is the same type as the object itself, just do something like this:

public class DataObjectImpl implements DataObject {
  public void copyFrom(final DataObject source) {
    if (source instanceof DataObjectImpl) {
      ...
    }
    else {
      ...
    }
  }
}

On the other hand, you could do it like this, using a different name for the method taking an implementation type. However, I don't see what good this does.

public interface DataObject<T extends DataObject<T>> {
  public void copyFrom(DataObject source);
  public void copyFromImpl(T source);
}

public class DataObjectImpl implements DataObject<DataObjectImpl> {
  public void copyFrom(final DataObject source) { ... }
  public void copyFromImpl(final DataObjectImpl source) { ... }
}