public void setSelectedItem(Object anItem) {
            selectedItem = (SingleTreeModel)anItem;
            Object[] listeners = listenerList.getListenerList();
            ListDataEvent e = null;

            for (int i = listeners.length - 2; i >= 0; i -= 2) {
                if (listeners[i] == ListDataListener.class) {
                    if (e == null) {
                        e = new ListDataEvent(this, ListDataEvent.CONTENTS_CHANGED, -1, -1);
                    }
                    ((ListDataListener)listeners[i+1]).contentsChanged(e);
                }
            }
        }