import javax.swing.*;import javax.swing.tree.*;import javax.swing.event.*;import java.awt.*;public class TreeExpandEventDemo2 extends JApplet {    DemoArea demoArea;    JTextArea textArea;    final static String newline = "\n";    public void init() {        GridBagLayout gridbag = new GridBagLayout();        GridBagConstraints c = new GridBagConstraints();        JPanel contentPane = new JPanel();        contentPane.setLayout(gridbag);        c.fill = GridBagConstraints.BOTH;        c.gridwidth = GridBagConstraints.REMAINDER;        c.weightx = 1.0;        c.weighty = 1.0;        c.insets = new Insets(1, 1, 1, 1);        demoArea = new DemoArea();        gridbag.setConstraints(demoArea, c);        contentPane.add(demoArea);        c.insets = new Insets(0, 0, 0, 0);        textArea = new JTextArea();        textArea.setEditable(false);        JScrollPane scrollPane = new JScrollPane(textArea);        scrollPane.setVerticalScrollBarPolicy(            JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);        scrollPane.setPreferredSize(new Dimension(200, 75));        gridbag.setConstraints(scrollPane, c);        contentPane.add(scrollPane);        setContentPane(contentPane);    }    void saySomething(String eventDescription, TreeExpansionEvent e) {        textArea.append(eventDescription + "; "                        + "path = " + e.getPath()                        + newline);    }    class DemoArea extends JScrollPane                   implements TreeExpansionListener,                              TreeWillExpandListener {        Dimension minSize = new Dimension(100, 100);        JTree tree;        Object[] willExpandOptions = {"Cancel Expansion", "Expand"};        String willExpandText = "A branch node is about to be expanded.\n"                              + "Click \"Cancel Expansion\" to prevent it.";        String willExpandTitle = "Tree Will Expand";            public DemoArea() {            TreeNode rootNode = createNodes();            tree = new JTree(rootNode);            tree.addTreeExpansionListener(this);            tree.addTreeWillExpandListener(this);            setViewportView(tree);        }        private TreeNode createNodes() {            DefaultMutableTreeNode root;            DefaultMutableTreeNode grandparent;            DefaultMutableTreeNode parent;            DefaultMutableTreeNode child;            root = new DefaultMutableTreeNode("San Francisco");            grandparent = new DefaultMutableTreeNode("Potrero Hill");            root.add(grandparent);            //            parent = new DefaultMutableTreeNode("Restaurants");            grandparent.add(parent);            child = new DefaultMutableTreeNode("Thai Barbeque");            parent.add(child);            child = new DefaultMutableTreeNode("Goat Hill Pizza");            parent.add(child);            //            parent = new DefaultMutableTreeNode("Grocery Stores");            grandparent.add(parent);            child = new DefaultMutableTreeNode("Good Life Grocery");            parent.add(child);            child = new DefaultMutableTreeNode("Safeway");            parent.add(child);                        grandparent = new DefaultMutableTreeNode("Noe Valley");            root.add(grandparent);            //            parent = new DefaultMutableTreeNode("Restaurants");            grandparent.add(parent);            child = new DefaultMutableTreeNode("Hamano Sushi");            parent.add(child);            child = new DefaultMutableTreeNode("Hahn's Hibachi");            parent.add(child);            //            parent = new DefaultMutableTreeNode("Grocery Stores");            grandparent.add(parent);            child = new DefaultMutableTreeNode("Real Foods");            parent.add(child);            child = new DefaultMutableTreeNode("Bell Market");            parent.add(child);                        return root;        }            public Dimension getMinimumSize() {            return minSize;        }        public Dimension getPreferredSize() {            return minSize;        }        // Required by TreeWillExpandListener interface.        public void treeWillExpand(TreeExpansionEvent e)                     throws ExpandVetoException {            saySomething("Tree-will-expand event detected", e);            int n = JOptionPane.showOptionDialog(                this, willExpandText, willExpandTitle,                JOptionPane.YES_NO_OPTION,                JOptionPane.QUESTION_MESSAGE,                null,                willExpandOptions,                willExpandOptions[1]);            if (n == 0) {                //User said cancel expansion.                saySomething("Tree expansion cancelled", e);                throw new ExpandVetoException(e);            }        }        // Required by TreeWillExpandListener interface.        public void treeWillCollapse(TreeExpansionEvent e) {            saySomething("Tree-will-collapse event detected", e);        }        // Required by TreeExpansionListener interface.        public void treeExpanded(TreeExpansionEvent e) {            saySomething("Tree-expanded event detected", e);        }        // Required by TreeExpansionListener interface.        public void treeCollapsed(TreeExpansionEvent e) {            saySomething("Tree-collapsed event detected", e);        }    }}