code: protected String getCalendarType() {
  
          CalendarType ct = this.getClass().getAnnotation(CalendarType.class);
  
          if (ct == null) {
              throw new IllegalStateException(
                  "Cannot find calendar type annotation: " + this.getClass());
          }
  
          return ct.value();
  
      }
docs: /*[deutsch]
  <p>Bestimmt das zugrundeliegende Kalendersystem. </p>
  
  @return  String describing the calendar
  @throws  IllegalStateException if the subclass does not have any
  annotation of type {@link net.time4j.format.CalendarType}
  @since   2.2