code: public static void reverse(final Object[] arr, final int pos, final int len) {
          for (int l = pos, r = pos + len - 1; l < r; l++, r--) {
              final Object tmp = arr[l];
              arr[l] = arr[r];
              arr[r] = tmp;
          }
      }
docs: Reverses the order of all elements in the given interval.
  
  @param arr array
  @param pos position of first element of the interval
  @param len length of the interval