code: public static void setDateFormat(String dateFormat) {
          Defaults.dateFormat = dateFormat;
          dateFormatHasTimeZone = false;
  
          if (dateFormat != null) {
              for (int i = 0; i < dateFormat.length(); i++) {
                  char ch = dateFormat.charAt(i);
  
                  if (ch == 'Z' || ch == 'z' || ch == 'V' || ch == 'v') {
                      dateFormatHasTimeZone = true;
                      break;
                  }
              }
          }
      }
docs: Sets the format used when encoding and decoding Dates. If the date
  format is set to {@code null}, dates will be encoded and decoded as
  timestamps (the number of milliseconds since the Unix epoch,
  1970-01-01).
  
  @param dateFormat the date format string
  @see com.google.gwt.i18n.shared.DateTimeFormat DateTimeFormat