code: private static Calendar buildCalendar() {
  
      Calendar calendar = calendarCache.get();
      if (calendar == null) {
        calendar = GregorianCalendar.getInstance();
        calendarCache.set(calendar);
      }
      return calendar;
    }
docs: Gets a calendar using the default time zone and locale. The Calendar
  returned is based on the current time in the default time zone with the
  default locale.
  
  @return a Calendar object.