Java 中文官方教程 2022 版（十九）（2）

protected void addButtons(JToolBar toolBar) {
    JButton button = null;
    //first button
    button = makeNavigationButton("Back24", PREVIOUS,
                                  "Back to previous something-or-other",
                                  "Previous");
    toolBar.add(button);
    //second button
    button = makeNavigationButton("Up24", UP,
                                  "Up to something-or-other",
                                  "Up");
    toolBar.add(button);
    *...//similar code for creating and adding the third button...*
}
protected JButton makeNavigationButton(String imageName,
                                       String actionCommand,
                                       String toolTipText,
                                       String altText) {
    //Look for the image.
    String imgLocation = "images/"
                         + imageName
                         + ".gif";
    URL imageURL = ToolBarDemo.class.getResource(imgLocation);
    //Create and initialize the button.
    JButton button = new JButton();
    button.setActionCommand(actionCommand);
    button.setToolTipText(toolTipText);
    button.addActionListener(this);
    if (imageURL != null) {                      //image found
        button.setIcon(new ImageIcon(imageURL, altText));
    } else {                                     //no image found
        button.setText(altText);
        System.err.println("Resource not found: " + imgLocation);
    }
    return button;
}

toolBar.setFloatable(false);

toolBar.setRollover(true);

toolBar.addSeparator();

//fourth button
button = new JButton("Another button");
...
toolBar.add(button);
//fifth component is NOT a button!
JTextField textField = new JTextField("A text field");
...
toolBar.add(textField);

b1.setToolTipText("Click this button to disable the middle button.");
b2.setToolTipText("This middle button does not react when you click it.");
b3.setToolTipText("Click this button to enable the middle button.");

*//Where instance variables are declared:*
private JTree tree;
...
public TreeDemo() {
    ...
    DefaultMutableTreeNode top =
        new DefaultMutableTreeNode("The Java Series");
    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("Books for Java Programmers");
    top.add(category);
    //original Tutorial
    book = new DefaultMutableTreeNode(new BookInfo
        ("The Java Tutorial: A Short Course on the Basics",
        "tutorial.html"));
    category.add(book);
    //Tutorial Continued
    book = new DefaultMutableTreeNode(new BookInfo
        ("The Java Tutorial Continued: The Rest of the JDK",
        "tutorialcont.html"));
    category.add(book);
    //Swing Tutorial
    book = new DefaultMutableTreeNode(new BookInfo
        ("The Swing Tutorial: A Guide to Constructing GUIs",
        "swingtutorial.html"));
    category.add(book);
    *//...add more books for programmers...*
    category = new DefaultMutableTreeNode("Books for Java Implementers");
    top.add(category);
    //VM
    book = new DefaultMutableTreeNode(new BookInfo
        ("The Java Virtual Machine Specification",
         "vm.html"));
    category.add(book);
    //Language Spec
    book = new DefaultMutableTreeNode(new BookInfo
        ("The Java Language Specification",
         "jls.html"));
    category.add(book);
}

*//Where the tree is initialized:*
    tree.getSelectionModel().setSelectionMode
            (TreeSelectionModel.SINGLE_TREE_SELECTION);
    //Listen for when the selection changes.
    tree.addTreeSelectionListener(this);
...
public void valueChanged(TreeSelectionEvent e) {
*//Returns the last path element of the selection.*
*//This method is useful only when the selection model allows a single selection.*
    DefaultMutableTreeNode node = (DefaultMutableTreeNode)
                       tree.getLastSelectedPathComponent();
    if (node == null)
    *//Nothing is selected.*     
    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);
}

*//...where the tree is initialized:*
    //Enable tool tips.
    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("This book is in the Tutorial series.");
        } else {
            setToolTipText(null); //no tool tip
        } 
        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;
    }
}