code: public final boolean isReadOnly() {
          Entry<?> entry = getEntry();
          Calendar calendar = entry.getCalendar();
          if (calendar != null) {
              return calendar.isReadOnly();
          }
  
          return false;
      }
docs: Convenience method to determine whether the entry belongs to a calendar
  that is read-only.
  
  @return true if the entry can not be edited by the user