public void addElement(Object element) {
if (!(element instanceof ChoiceItem))
throw new IllegalArgumentException(
"element has to be of type ChoiceItem, but is of type " + element.getClass().getName());
super.addElement(element);
}
public void insertElementAt(Object o, int index) {
if (!(o instanceof ChoiceItem))
throw new IllegalArgumentException(
"Added objects has to be of type ChoiceItem. Object was of type "
+ o.getClass().getName());
super.insertElementAt(o, index);
}