code: public Calendar getSharedCalendar(TimeZone timeZone) {
      if (timeZone == null) {
        timeZone = getDefaultTz();
      }
      Calendar tmp = calendarWithUserTz;
      tmp.setTimeZone(timeZone);
      return tmp;
    }
docs: Get a shared calendar, applying the supplied time zone or the default time zone if null.
  
  @param timeZone time zone to be set for the calendar
  @return The shared calendar.