code: public static <T, L extends List<T>> L sortThis(L list, Comparator<? super T> comparator)
      {
          if (list instanceof MutableList)
          {
              ((MutableList<T>) list).sortThis(comparator);
          }
          else if (list instanceof ArrayList)
          {
              ArrayListIterate.sortThis((ArrayList<T>) list, comparator);
          }
          else
          {
              if (list.size() > 1)
              {
                  Collections.sort(list, comparator);
              }
          }
          return list;
      }
docs: SortThis is a mutating method.  The List passed in is also returned.