求教一个JTree监听的有关问题

//中忙你写了个，看看吧import java.awt.Color;import javax.swing.*;import javax.swing.event.TreeSelectionEvent;import javax.swing.event.TreeSelectionListener;import javax.swing.tree.DefaultMutableTreeNode;import javax.swing.tree.DefaultTreeCellRenderer;import javax.swing.tree.DefaultTreeModel;import javax.swing.tree.TreePath;public class TestJTree implements TreeSelectionListener {    JTree tree;    DefaultMutableTreeNode root;    DefaultTreeModel model;    JSplitPane mainSplitpane;    public TestJTree() {        mainSplitpane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT); // 分割面板                        model = new DefaultTreeModel(root); // 设置树的缺省模式        tree = new JTree(model);        root = new DefaultMutableTreeNode("TestTree");//树根        DefaultMutableTreeNode level1 = new DefaultMutableTreeNode("A");        DefaultMutableTreeNode level2 = new DefaultMutableTreeNode("分支1"); // 树叶        DefaultMutableTreeNode level3 = new DefaultMutableTreeNode("分支2");        level1.add(level2);        level1.add(level3);        root.add(level1);        tree = new JTree(root);        DefaultTreeCellRenderer render = new DefaultTreeCellRenderer(); // 树叶        render.setTextSelectionColor(Color.blue); // 选择时候的颜色        render.setTextNonSelectionColor(Color.black); // 非选择时候颜色        tree.setCellRenderer(render);        tree.addTreeSelectionListener(this);                JPanel firstimg = new JPanel();        firstimg.setLayout(null);        ImageIcon img = new ImageIcon("img/firstimg.jpg");        JLabel imgLabel = new JLabel(img); // 面板，此处实际是一张图片        imgLabel.setBounds(0, 0, img.getIconWidth(), img                .getIconHeight());        firstimg.add(imgLabel);                mainSplitpane.setDividerLocation(185);        mainSplitpane.setLeftComponent(tree);        mainSplitpane.setRightComponent(firstimg);                JFrame jf = new JFrame("TestTree");        jf.setSize(900, 600);        jf.setContentPane(mainSplitpane);        jf.setLocationRelativeTo(null);        jf.setVisible(true);        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);            }    public void valueChanged(TreeSelectionEvent e) {        if (e.getSource() == tree) {            DefaultMutableTreeNode node = (DefaultMutableTreeNode) tree                    .getLastSelectedPathComponent();            if (node.isLeaf()) {                System.out.println(node.toString());                TreePath visiblePath = new TreePath(model.getPathToRoot(node));                System.out.println(visiblePath.toString());                if (node.toString().equals("分支1")) {                    //mainSplitpane.setRightComponent(...do what you want here...);   重点在这里                }            }        }    }    public static void main(String[] args) {        new TestJTree();    }}