code: public void setTimeZone(TimeZone zone)
      {
          // zone is cloned once for all three usages below:
          TimeZone zoneToSet = (TimeZone)zone.clone();
          if (fDateFormat != null) {
              fDateFormat.setTimeZone(zoneToSet);
          }
          // fDateFormat has the master calendar for the DateIntervalFormat;
          // fFromCalendar and fToCalendar are internal work clones of that calendar.
          if (fFromCalendar != null) {
              fFromCalendar.setTimeZone(zoneToSet);
          }
          if (fToCalendar != null) {
              fToCalendar.setTimeZone(zoneToSet);
          }
      }
docs: Set the TimeZone for the calendar used by this DateIntervalFormat object.
  @param zone The new TimeZone, will be cloned for use by this DateIntervalFormat.