翻译:java中怎样使用树结构(How to Use Trees)

     最近闲的慌,听说思维迟缓是衰老的标志,.为了尽量保持年轻,我对java 2 jdk的JTree的应用做了一个翻译,首次尝试翻译,有许多不对的地方,还请高手指正.

        怎样使用树结构(How to Use Trees)(一)

       使用Jtree类,你可以展示有层次关系的数据.一个JTree的实例并不包含你的数据,它只是简单的展示一下你的数据而已.象其他的Swing组件一样,树通过查询它的数据模型得到数据,下面是关于树结构的图片:

         如前所述,JTree垂直的展示它的数据.每一行展示一条树结构的数据,被称作一个”节点”每个树结构都有一个根节点,所有其它节点都由此派生而来.默认的,树结构将显示根节点,但是你也可以做另外的处理.一个节点可以拥有子节点,也可以没有子节点.我们提到的有子节点的节点,叫做分支节点.没有子节点的节点叫做叶节点(leaf nodes).分支节点可以拥有任意多的子节点.用户可以通过点击分支节点来折叠或者展开它----使它的子节点可见或者不可见.默认的,除开根节点的所有分支节点的初始状态都是折叠的.通过监听树结构的扩展事件,程序可以发现分支节点的扩展状态是否改变.

本文余下部分将讨论如下主题:

增加一个树结构

响应节点选择事件

个性花树结构的显示

动态改变树结构

增加一个数字模型

Tree API

使用树的一些例子

 

 

 

增加一个树结构

下面是一个应用的图片,上半部分在一个可滚动面板中展示了一个树结构

1:用Java Web Start运行TreeDemo.或者自己动手编译如下代码:

文件名称:TreeDemo.java

/**

 * A 1.4 application that requires the following additional files:

 *   TreeDemoHelp.html

 *    arnold.html

 *    bloch.html

 *    chan.html

 *    jls.html

 *    swingtutorial.html

 *    tutorial.html

 *    tutorialcont.html

 *    vm.html

 */

import javax.swing.JEditorPane;

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.JScrollPane;

import javax.swing.JSplitPane;

import javax.swing.UIManager;

 

 

 

import javax.swing.JTree;

import javax.swing.tree.DefaultMutableTreeNode;

import javax.swing.tree.TreeSelectionModel;

import javax.swing.event.TreeSelectionEvent;

import javax.swing.event.TreeSelectionListener;

 

 

 

import java.net.URL;

import java.io.IOException;

import java.awt.Dimension;

import java.awt.GridLayout;

 

 

 

public class TreeDemo extends JPanel

                      implements TreeSelectionListener {

    private JEditorPane htmlPane;

    private JTree tree;

    private URL helpURL;

    private static boolean DEBUG = false;

 

 

 

    //Optionally play with line styles.  Possible values are

    //"Angled" (the default), "Horizontal", and "None".

    private static boolean playWithLineStyle = false;

    private static String lineStyle = "Horizontal";

   

    //Optionally set the look and feel.

    private static boolean useSystemLookAndFeel = false;

 

 

 

    public TreeDemo() {

        super(new GridLayout(1,0));

 

 

 

        //Create the nodes.

        DefaultMutableTreeNode top =

            new DefaultMutableTreeNode("The Java Series");

        createNodes(top);

 

 

 

        //Create a tree that allows one selection at a time.

        tree = new JTree(top);

        tree.getSelectionModel().setSelectionMode

                (TreeSelectionModel.SINGLE_TREE_SELECTION);

 

 

 

        //Listen for when the selection changes.

        tree.addTreeSelectionListener(this);

 

 

 

        if (playWithLineStyle) {

            System.out.println("line style = " + lineStyle);

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

        }

 

 

 

        //Create the scroll pane and add the tree to it.

        JScrollPane treeView = new JScrollPane(tree);

 

 

 

        //Create the HTML viewing pane.

        htmlPane = new JEditorPane();

        htmlPane.setEditable(false);

        initHelp();

        JScrollPane htmlView = new JScrollPane(htmlPane);

 

 

 

        //Add the scroll panes to a split pane.

        JSplitPane splitPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT);

        splitPane.setTopComponent(treeView);

        splitPane.setBottomComponent(htmlView);

 

 

 

        Dimension minimumSize = new Dimension(100, 50);

        htmlView.setMinimumSize(minimumSize);

        treeView.setMinimumSize(minimumSize);

        splitPane.setDividerLocation(100); //XXX: ignored in some releases

                                           //of Swing. bug 4101306

        //workaround for bug 4101306:

        //treeView.setPreferredSize(new Dimension(100, 100));

 

 

 

        splitPane.setPreferredSize(new Dimension(500, 300));

 

 

 

        //Add the split pane to this panel.

        add(splitPane);

    }

 

 

 

    /** Required by TreeSelectionListener interface. */

    public void valueChanged(TreeSelectionEvent e) {

        DefaultMutableTreeNode node = (DefaultMutableTreeNode)

                           tree.getLastSelectedPathComponent();

 

 

 

        if (node == null) return;

 

 

 

        Object nodeInfo = node.getUserObject();

        if (node.isLeaf()) {

            BookInfo book = (BookInfo)nodeInfo;

            displayURL(book.bookURL);

            if (DEBUG) {

                System.out.print(book.bookURL + ":  /n    ");

            }

        } else {

            displayURL(helpURL);

        }

        if (DEBUG) {

            System.out.println(nodeInfo.toString());

        }

    }

 

 

 

    private class BookInfo {

        public String bookName;

        public URL bookURL;

 

 

 

        public BookInfo(String book, String filename) {

            bookName = book;

            bookURL = TreeDemo.class.getResource(filename);

            if (bookURL == null) {

                System.err.println("Couldn't find file: "

                                   + filename);

            }

        }

 

 

 

        public String toString() {

            return bookName;

        }

    }

 

 

 

    private void initHelp() {

        String s = "TreeDemoHelp.html";

        helpURL = TreeDemo.class.getResource(s);

        if (helpURL == null) {

            System.err.println("Couldn't open help file: " + s);

        } else if (DEBUG) {

            System.out.println("Help URL is " + helpURL);

        }

 

 

 

        displayURL(helpURL);

    }

 

 

 

    private void displayURL(URL url) {

        try {

            if (url != null) {

                htmlPane.setPage(url);

            } else { //null url

      htmlPane.setText("File Not Found");

                if (DEBUG) {

                    System.out.println("Attempted to display a null URL.");

                }

            }

        } catch (IOException e) {

            System.err.println("Attempted to read a bad URL: " + url);

        }

    }

 

 

 

    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);

 

 

 

        //JFC Swing Tutorial

        book = new DefaultMutableTreeNode(new BookInfo

            ("The JFC Swing Tutorial: A Guide to Constructing GUIs",

            "swingtutorial.html"));

        category.add(book);

 

 

 

        //Bloch

        book = new DefaultMutableTreeNode(new BookInfo

            ("Effective Java Programming Language Guide",

        "bloch.html"));

        category.add(book);

 

 

 

        //Arnold/Gosling

        book = new DefaultMutableTreeNode(new BookInfo

            ("The Java Programming Language", "arnold.html"));

        category.add(book);

 

 

 

        //Chan

        book = new DefaultMutableTreeNode(new BookInfo

            ("The Java Developers Almanac",

             "chan.html"));

        category.add(book);

 

 

 

        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);

    }

       

    /**

     * Create the GUI and show it.  For thread safety,

     * this method should be invoked from the

     * event-dispatching thread.

     */

    private static void createAndShowGUI() {

        if (useSystemLookAndFeel) {

            try {

                UIManager.setLookAndFeel(

                    UIManager.getSystemLookAndFeelClassName());

            } catch (Exception e) {

                System.err.println("Couldn't use system look and feel.");

            }

        }

 

 

 

        //Make sure we have nice window decorations.

        JFrame.setDefaultLookAndFeelDecorated(true);

 

 

 

        //Create and set up the window.

        JFrame frame = new JFrame("TreeDemo");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

 

 

 

        //Create and set up the content pane.

        TreeDemo newContentPane = new TreeDemo();

        newContentPane.setOpaque(true); //content panes must be opaque

        frame.setContentPane(newContentPane);

 

 

 

        //Display the window.

        frame.pack();

        frame.setVisible(true);

    }

 

 

 

    public static void main(String[] args) {

        //Schedule a job for the event-dispatching thread:

        //creating and showing this application's GUI.

        javax.swing.SwingUtilities.invokeLater(new Runnable() {

            public void run() {

                createAndShowGUI();

            }

        });

    }

}

2:展开节点

点击节点左侧的圆圈图标可展开节点

3:收缩节点

点击节点左侧的圆圈图标可收缩节点

下面分析一下TreeDemo.java代码:

增加JTree实例并且把它放到面板上:

//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);

    ...

}

代码增加了一个DefaultMutableTreeNode的实例,作为树结构的根节点.然后增加树

结构余下的节点.接着,增加树,根节点作为JTree的构造器的一个参数.最后,把tree放到面板中,

下面是在根节点下面增加子节点的代码:

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);

    //JFC Swing Tutorial

    book = new DefaultMutableTreeNode(new BookInfo

        ("The JFC 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);

}

DefaultMutableTreeNode构造器的参数是一个用户实例,此实例包含或者指向一个

和树节点关联的数据.用户实例可以是一个string字符串,或者是一个用户自己的对

象实例.如果你实现了一个用户自己的对象实例,你应该实现toString方法,以便返回

一个string字符串并在节点上显示.

例如:上面代码用到的BookInfo类是一个用户自己的类,它包含两方面的数据:书名和

描述书详细信息的html文件的url地址.在这个class中,toString被重载用来返回书名.

因而,每一个和BookInfo实例关联的节点都可以显示书名.

总之:你可以通过调用JTree的构造器,设定根节点作为参数的方法增加一个tree.你也可以把

tree放入一个可滚动的面板,这样tree就不会占用很大的空间.你不必为节点的展开和搜索写

任何代码.然后,如果你想让tree响应你点击选择一个节点的话,你还是要增加一些代码的.

响应节点选择事件(续)

响应树节点的选择事件其实蛮简单,你可以实现一个树的选择监听器并且注册,下面的代码是TreeDemo中有关选择监听的代码:

//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) {

    DefaultMutableTreeNode node = (DefaultMutableTreeNode)

                       tree.getLastSelectedPathComponent();

    if (node == null) return;

    Object nodeInfo = node.getUserObject();

    if (node.isLeaf()) {

        BookInfo book = (BookInfo)nodeInfo;

        displayURL(book.bookURL);

    } else {

        displayURL(helpURL); 

    }

}

上面的代码完成如下任务:

1:得到tree的默认TreeSelectionModel,并且设置选择模式,以便在同一时间,只有一个节点被选择

2:对tree注册一个事件处理器.这个事件处理器是一个实现了TreeSelectionListener接口的对象.

3:在事件处理器中,通过调用tree的getLastSelectedPathComponent方法来判断是哪个节点被选择了.

4:调用getUserObject方法来得到和节点绑定在一起的数据.