Error in proposed Collections.sort signature

Question

(A very long time ago I've send a note on this to the jsr comment list, but unfortunately I never got a reply nor did I notice a bug report. Therefore I propose the change again here).
The signature of the Collections.sort method is very limiting:
  static <T> void sort(List<T> list, Comparator<T> c);This signature requires you to pass a Comparator that is parameterized with exactly the same type as the items in the List. However, often Comparators can be implemented more generic. The signature doesn't allow this. The only requirement for the sort algorithm is however to pass a Comparator that is able to compare the items in the List.
This requirement is expressed by the following signature:
  static <T, E extends T> void sort(List<E> list, Comparator<T> comparator) The items in the List are now allowed to be more specific. Because I don't want to cast in Generic Java code I've implemented a tiny workaround:
  public static <T, E extends T> void sort(List<E> list, Comparator<T> comparator) {
    Collections.sort(list, new ComparatorWrapper<T, E>(comparator));
  private static class ComparatorWrapper<T, E extends T> implements Comparator<E> {
    private Comparator<T> _comparator;
    public ComparatorWrapper(Comparator<T> comparator) {
      super();
      _comparator = comparator;
    public int compare(E o1, E o2) {
      return _comparator.compare(o1, o2);
  }This proves the correctness of the new signature. This also proves that you have to be very careful in chosing a signature. I've been working with Generic Java for some years now, but I'm still making the same mistake now and then ...

Answer 1

This will be fixed in a novel and interesting way in the new spec for GJ -- stay tuned! (I think mid-May/late-May is the expected timeframe for this.)