code: public static Calendar toCalendar(final Instant self) {
          Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
          cal.setTime(toDate(self));
          return cal;
      }
docs: Returns a generally equivalent {@link java.util.Calendar} in the GMT time zone, truncated to milliseconds.
  
  @param self an Instant
  @return a Calendar
  @since 2.5.0