Java JTree handle tree expansion event

import java.awt.BorderLayout;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.event.TreeExpansionEvent;
import javax.swing.event.TreeExpansionListener;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.TreePath;

public class Main {
   public static void main(String args[]) {
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

      DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");
      root.add(new DefaultMutableTreeNode("A"));
      root.add(new DefaultMutableTreeNode("B"));
      root.add(new DefaultMutableTreeNode("C"));
      JTree tree = new JTree(root);

      TreeExpansionListener treeExpandListener = new TreeExpansionListener() {

         public void treeExpanded(TreeExpansionEvent event) {
            TreePath path = event.getPath();
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) path.getLastPathComponent();
            String data = node.getUserObject().toString();
            System.out.println("Expanded: " + data);
         }//w  w  w  . j  a v  a2  s .c o  m

         public void treeCollapsed(TreeExpansionEvent event) {
            TreePath path = event.getPath();
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) path.getLastPathComponent();
            String data = node.getUserObject().toString();
            System.out.println("Collapsed: " + data);
         }
      };

      tree.addTreeExpansionListener(treeExpandListener);

      JScrollPane scrollPane = new JScrollPane(tree);
      frame.add(scrollPane, BorderLayout.CENTER);
      frame.setSize(300, 150);
      frame.setVisible(true);

   }
}