code: public static Calendar popCalendar()
     {
        Calendar result;
        Deque<Calendar> calendars = CALENDARS.get();
        if (calendars.isEmpty())
        {
           result = Calendar.getInstance();
        }
        else
        {
           result = calendars.pop();
        }
        return result;
     }
docs: Acquire a calendar instance.
  
  @return Calendar instance