code: public int getIndex(Object key) {
      int[] nums = (int[]) cset.get(key);
      if (nums == null) {
        return -1;
      }
      else {
        return nums[1];
      }
    }
docs: Returns the index for the specified key or -1 if specified value is not contain in this set.
  @param key The key to be checked.
  @return the index for the specified value or -1 if specified value is not contain in this set