code: public SortedSet<Date> getDates(Boolean checkState) {
  
          TreeSet<Date> result = new TreeSet<Date>();
          for (CmsCheckBox cb : m_checkBoxes) {
              if ((checkState == null) || (cb.isChecked() == checkState.booleanValue())) {
                  Date date = (Date)cb.getElement().getPropertyObject("date");
                  result.add(date);
              }
          }
          return result;
      }
docs: Returns all dates with the specified check state, if the check state is <code>null</code>, all dates are returned.
  @param checkState the check state, the returned dates should have.
  @return all dates with the specified check state, if the check state is <code>null</code>, all dates are returned.