code: @Override
    public int compare(S solution1, S solution2) {
      int result = rankComparator.compare(solution1, solution2) ;
      if (result == 0) {
        result = crowdingDistanceComparator.compare(solution1, solution2);
      }
  
      return result;
    }
docs: Compares two solutions.
  
  @param solution1 Object representing the first solution
  @param solution2 Object representing the second solution.
  @return -1, or 0, or 1 if solution1 is less than, equal, or greater than solution2,
  respectively.