Java 8 - Call interface's default method with double colon syntax

Question

I'm delving into the Java 8 innovations, and I'm trying to call a default method which I implement in a high-level interface, even when a subclass overrides it. I would have no problem going back to implementing a Comparator in my BusinessLogic class, but I was wondering if there's some magic that lets me use the nifty new ::.

Code:

public interface IdEntity extends Comparable<IdEntity> {

    int getId();

    @Override
    default int compareTo(IdEntity other) {
        return getId() - other.getId();
    }
}

public class Game implements IdEntity {
    @Override
    public int compareTo(IdEntity o) {
        if (o instanceof Game) {
            Game other = (Game) o;
            int something;
            // logic
            return something;
        }
        return super.compareTo(o);
    }
}

public class BusinessLogic {
    private void sortList(List<? extends IdEntity> list) {
        // for Game, Game::compareTo gets called but I want, in this call only, the default method
        Collections.sort(list, IdEntity::compareTo);
    }
}

Answer 1

One way would be to put the compare method in a static method:

public static interface IdEntity extends Comparable<IdEntity> {
  int getId();
  @Override default int compareTo(IdEntity other) {
    return defaultCompare(this, other);
  }
  static int defaultCompare(IdEntity first, IdEntity second) {
    return first.getId() - second.getId();
  }
}

Then your method would be:

Collections.sort(list, IdEntity::defaultCompare);

Answer 2

Simpler approach: static import Comparator.comparingInt and use

Collections.sort(list, comparingInt(IdEntity::getId));

I don't believe you can re-extract the default compareTo implementation: it's been overridden; you usually can't run an overridden method implementation. But this will just work straightforwardly.