code: @SafeVarargs
      public final void addCalendarListeners(ListChangeListener<Calendar>... listeners) {
          if (listeners != null) {
              for (ListChangeListener<Calendar> listener : listeners) {
                  getCalendars().addListener(listener);
              }
          }
      }
docs: Adds the given calendar listener in order to get notified when any calendar/entry changes.
  
  @param listeners The listener.