/** Return the current state, which is determined by the selection status of the model. */
 public Boolean getState() {
   return model.getState();
 }
 /**
  * Set the new state to either SELECTED, NOT_SELECTED or DONT_CARE. If state == null, it is
  * treated as DONT_CARE.
  */
 public void setState(Boolean state) {
   model.setState(state);
 }