code: @Override public int compareTo(Program that) {
  
        int cmp = Integer.compare(depth, that.depth);
        if (cmp == 0)
        {
           return Integer.compare(length, that.length);
        } else {
           return cmp;
        }
     }
docs: The method return -1 if this program is better than that program
  @param that
  @return