code: public static int d(BitSet x, BitSet y) {
          if (x.size() != y.size())
              throw new IllegalArgumentException(String.format("BitSets have different length: x[%d], y[%d]", x.size(), y.size()));
  
          int dist = 0;
          for (int i = 0; i < x.size(); i++) {
              if (x.get(i) != y.get(i))
                  dist++;
          }
  
          return dist;
      }
docs: Returns Hamming distance between the two BitSets.