AbstractList etc. functionality as interfaces with default methods?

[Attila Szegedi]

So I’m in a position where I’d need to have a class implement List, but it already extends something else, so I can’t have it extend AbstractList, which leaves me with a lot of boilerplate methods to implement.

Would it seem like a good idea to reimagine AbstractList and friends as interfaces with default methods? 

Of course, I know that technically for backwards compatibility we can’t really do this, but what we could do is:

public interface DefaultList<T> extends List<T> {
    … add all methods from AbstractList here as default methods …
}

public abstract class AbstractList<T> implements DefaultList<T> {
}

(I’ll hand-wave the issue of “protected int modCount” issue for now.)

Actually, this seems like such an obvious idea that I’m 100% sure it must’ve been considered before, but I can’t find any related discussion.

Attila.