code: private int hammingDistance(String simHash1, String simHash2) {
          if (simHash1.length() != simHash2.length()) {
              return -1;
          }
          int distance = 0;
          int len = simHash1.length();
          for (int i = 0; i < len; i++) {
              if (simHash1.charAt(i) != simHash2.charAt(i)) {
                  distance++;
              }
          }
          return distance;
      }
docs: 计算等长的SimHash值的汉明距离
  如不能比较距离（比较的两段文本长度不相等），则返回-1
  @param simHash1 SimHash值1
  @param simHash2 SimHash值2
  @return 汉明距离