public long toLong() {
    switch (this) {
      case _0:
        return 0L;
      case _1:
        return 1L;
      case _2:
        return 2L;
      case _3:
        return 3L;
      case _4:
        return 4L;
      case _5:
        return 5L;
      case _6:
        return 6L;
      case _7:
        return 7L;
      case _8:
        return 8L;
      default:
        return 9L;
    }
  }