code: private String formatSecondaryDate(@NonNull Calendar date) {
          if(secondaryDateFormat == null)
              return DateUtils.formatDateTime(getContext(), date.getTimeInMillis(),
                      DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_NUMERIC_DATE);
          else
              return secondaryDateFormat.format(date.getTime());
      }
docs: only to be used when FLAG_NUMBERS and FLAG_WEEKDAY_NAMES have been set