code: public void setMonth(int month)
    {
      if (month < 0 || DAYS_IN_MONTH.length <= month)
        return;
  
      _month = month;
  
      if (DAYS_IN_MONTH[month] <= _dayOfMonth)
        _dayOfMonth = DAYS_IN_MONTH[month] - 1;
  
      calculateJoin();
      calculateSplit(_localTimeOfEpoch);
    }
docs: Sets the month in the year.