如何使用树形结构

//在此处声明实例变量：
private JTree tree;
...
public TreeDemo() {
    ...
    DefaultMutableTreeNode top =
        new DefaultMutableTreeNode("Java系列");
    createNodes(top);
    tree = new JTree(top);
    ...
    JScrollPane treeView = new JScrollPane(tree);
    ...
}

private void createNodes(DefaultMutableTreeNode top) {
    DefaultMutableTreeNode category = null;
    DefaultMutableTreeNode book = null;
    
    category = new DefaultMutableTreeNode("面向Java程序员的图书");
    top.add(category);
    
    //原始教程
    book = new DefaultMutableTreeNode(new BookInfo
        ("Java教程：基础知识简短课程",
        "tutorial.html"));
    category.add(book);
    
    //继续教程
    book = new DefaultMutableTreeNode(new BookInfo
        ("Java教程继续：JDK的其他部分",
        "tutorialcont.html"));
    category.add(book);
    
    //Swing教程
    book = new DefaultMutableTreeNode(new BookInfo
        ("Swing教程：构建GUI的指南",
        "swingtutorial.html"));
    category.add(book);

    //...添加更多面向程序员的图书...

    category = new DefaultMutableTreeNode("面向Java实现者的图书");
    top.add(category);

    //虚拟机
    book = new DefaultMutableTreeNode(new BookInfo
        ("Java虚拟机规范",
         "vm.html"));
    category.add(book);

    //语言规范
    book = new DefaultMutableTreeNode(new BookInfo
        ("Java语言规范",
         "jls.html"));
    category.add(book);
}

//树的初始化：
    tree.getSelectionModel().setSelectionMode
            (TreeSelectionModel.SINGLE_TREE_SELECTION);

    //监听选择变化。
    tree.addTreeSelectionListener(this);
...
public void valueChanged(TreeSelectionEvent e) {
//返回选择的最后一个路径元素。
//只有在选择模型允许单选时，此方法才有用。
    DefaultMutableTreeNode node = (DefaultMutableTreeNode)
                       tree.getLastSelectedPathComponent();

    if (node == null)
    //未选择任何节点。     
    return;

    Object nodeInfo = node.getUserObject();
    if (node.isLeaf()) {
        BookInfo book = (BookInfo)nodeInfo;
        displayURL(book.bookURL);
    } else {
        displayURL(helpURL); 
    }
}

tree.putClientProperty("JTree.lineStyle", "Horizontal");

tree.putClientProperty("JTree.lineStyle", "None");

ImageIcon leafIcon = createImageIcon("images/middle.gif");
if (leafIcon != null) {
    DefaultTreeCellRenderer renderer = 
        new DefaultTreeCellRenderer();
    renderer.setLeafIcon(leafIcon);
    tree.setCellRenderer(renderer);
}

//...树初始化的地方:
    //启用工具提示。
    ToolTipManager.sharedInstance().registerComponent(tree);
    
    ImageIcon tutorialIcon = createImageIcon("images/middle.gif");
    if (tutorialIcon != null) {
        tree.setCellRenderer(new MyRenderer(tutorialIcon));
    }
...
class MyRenderer extends DefaultTreeCellRenderer {
    Icon tutorialIcon;

    public MyRenderer(Icon icon) {
        tutorialIcon = icon;
    }

    public Component getTreeCellRendererComponent(
                        JTree tree,
                        Object value,
                        boolean sel,
                        boolean expanded,
                        boolean leaf,
                        int row,
                        boolean hasFocus) {

        super.getTreeCellRendererComponent(
                        tree, value, sel,
                        expanded, leaf, row,
                        hasFocus);
        if (leaf && isTutorialBook(value)) {
            setIcon(tutorialIcon);
            setToolTipText("这本书是教程系列的。");
        } else {
            setToolTipText(null); //没有工具提示
        } 

        return this;
    }

    protected boolean isTutorialBook(Object value) {
        DefaultMutableTreeNode node =
                (DefaultMutableTreeNode)value;
        BookInfo nodeInfo =
                (BookInfo)(node.getUserObject());
        String title = nodeInfo.bookName;
        if (title.indexOf("Tutorial") >= 0) {
            return true;
        }

        return false;
    }
}

rootNode = new DefaultMutableTreeNode("根节点");
treeModel = new DefaultTreeModel(rootNode);
treeModel.addTreeModelListener(new MyTreeModelListener());

tree = new JTree(treeModel);
tree.setEditable(true);
tree.getSelectionModel().setSelectionMode
        (TreeSelectionModel.SINGLE_TREE_SELECTION);
tree.setShowsRootHandles(true);

class MyTreeModelListener implements TreeModelListener {
    public void treeNodesChanged(TreeModelEvent e) {
        DefaultMutableTreeNode node;
        node = (DefaultMutableTreeNode)
                 (e.getTreePath().getLastPathComponent());

        /*
         * 如果事件列出了子节点，则更改的节点是我们已经获取到的节点的子节点。
         * 否则，更改的节点和指定的节点是相同的。
         */
        try {
            int index = e.getChildIndices()[0];
            node = (DefaultMutableTreeNode)
                   (node.getChildAt(index));
        } catch (NullPointerException exc) {}

        System.out.println("用户已完成对节点的编辑。");
        System.out.println("新值：" + node.getUserObject());
    }
    public void treeNodesInserted(TreeModelEvent e) {
    }
    public void treeNodesRemoved(TreeModelEvent e) {
    }
    public void treeStructureChanged(TreeModelEvent e) {
    }
}

treePanel.addObject("New Node " + newNodeSuffix++);
...
public DefaultMutableTreeNode addObject(Object child) {
    DefaultMutableTreeNode parentNode = null;
    TreePath parentPath = tree.getSelectionPath();

    if (parentPath == null) {
        // 没有选择。默认为根节点。
        parentNode = rootNode;
    } else {
        parentNode = (DefaultMutableTreeNode)
                     (parentPath.getLastPathComponent());
    }

    return addObject(parentNode, child, true);
}
...
public DefaultMutableTreeNode addObject(DefaultMutableTreeNode parent,
                                        Object child,
                                        boolean shouldBeVisible) {
    DefaultMutableTreeNode childNode =
            new DefaultMutableTreeNode(child);
    ...
    treeModel.insertNodeInto(childNode, parent,
                             parent.getChildCount());

    // 确保用户可以看到新节点。
    if (shouldBeVisible) {
        tree.scrollPathToVisible(new TreePath(childNode.getPath()));
    }
    return childNode;
}

class DemoArea extends JScrollPane
                   implements TreeWillExpandListener {
        .......
        .......

        private TreeNode createNodes() {
            DefaultMutableTreeNode root;
            DefaultMutableTreeNode grandparent;
            DefaultMutableTreeNode parent;

            root = new DefaultMutableTreeNode("San Francisco");

            grandparent = new DefaultMutableTreeNode("Potrero Hill");
            root.add(grandparent);

            parent = new DefaultMutableTreeNode("Restaurants");
            grandparent.add(parent);
            
            dummyParent = parent;
            return root;
        }

TreeNode rootNode = createNodes();
tree = new JTree(rootNode);
tree.addTreeExpansionListener(this);
tree.addTreeWillExpandListener(this);
.......
.......
setViewportView(tree);

private void 加载延迟子节点(){
            DefaultMutableTreeNode child;
            child = new DefaultMutableTreeNode("泰式烧烤");
            dummyParent.add(child);
            child = new DefaultMutableTreeNode("山羊山披萨");
            dummyParent.add(child);
            textArea.append(" 泰式烧烤和山羊山披萨已被延迟加载");
        }

        .......
        .......

public void treeWillExpand(TreeExpansionEvent e) 
                    throws ExpandVetoException {
            saySomething("您即将展开节点 ", e);
            int n = JOptionPane.showOptionDialog(
                this, willExpandText, willExpandTitle,
                JOptionPane.YES_NO_OPTION,
                JOptionPane.QUESTION_MESSAGE,
                null,
                willExpandOptions,
                willExpandOptions[1]);
           
        加载延迟子节点();
        }