code: public long toNanoOfDay() {
          long total = hour * NANOS_PER_HOUR;
          total += minute * NANOS_PER_MINUTE;
          total += second * NANOS_PER_SECOND;
          total += nano;
          return total;
      }
docs: Extracts the time as nanos of day,
  from {@code 0} to {@code 24 * 60 * 60 * 1,000,000,000 - 1}.
  
  @return the nano of day equivalent to this time