code: public final synchronized StringBuffer format(DateInterval dtInterval,
                                       StringBuffer appendTo,
                                       FieldPosition fieldPosition)
      {
          fFromCalendar.setTimeInMillis(dtInterval.getFromDate());
          fToCalendar.setTimeInMillis(dtInterval.getToDate());
          return format(fFromCalendar, fToCalendar, appendTo, fieldPosition);
      }
docs: Format a DateInterval to produce a string.
  
  @param dtInterval        DateInterval to be formatted.
  @param appendTo          Output parameter to receive result.
  Result is appended to existing contents.
  @param fieldPosition     On input: an alignment field, if desired.
  On output: the offsets of the alignment field.
  There may be multiple instances of a given field type
  in an interval format; in this case the fieldPosition
  offsets refer to the first instance.
  @return                  Reference to 'appendTo' parameter.