借助swing体系的mvc设计理念，为组件更换不同的外观成为轻而易举的事情。本文主要以JList和JComboBox为例讲解ListCellRenderer的原理与用法.

一、绘制器的工作原理
不管是JList还是JComboBox，它们都用到了ListCellRenderer,因为JComboBox本身就是由一个下拉式的JList和TextField组成的. 在这里，它们使用了callback的机制。

callback的一是种常见的方式是在A类中调用B类中的方法，在A类中先要登记一个(也可以是多个)B类的实例引用，在需要调用时再通过该实例来调用它的内部方法.这样的机制在很多的设计模式中都有用到，如Observer等.还有AWT的事件机制也用到了callback.

要实现callback，通常将B类设计成一个能被callback的接口.在JList的绘制器中，swing提供了一个ListCellRenderer接口，
public interface ListCellRenderer {
    Component getListCellRendererComponent(
        JList list,
        Object value,
        int index,
        boolean isSelected,
        boolean cellHasFocus);
}
这个接口只提供一个方法，我们只要实现了这个接口，并将它的实例引用传给JList,就可以将JList替换成不同的样式了.看一下ListCellRenderer是如何工作的,

在绘制JList的每个Cell之前,它会去调用getListCellComponent( ),得到一个Component,并
将这个Component绘制在正确的位置.因为getListCellComponent( )返回的是Component,所以我们几乎可以扩展任意一个Component,来改变JList,JComboBox等的外观.

二、制作自已的绘制器
我们现在要想让JList中显示一组学生名单，同时每个名单前显示该学生的图标.如下图所示

我们先来想一想，Swing中有什么组件既可以显示图标也可以显示文字? JLabel.对了。我们就用JLabel作为JList的绘制器,　看看我扩展的JLabel类，它实现了ListCellRenderer接口:
        /* 可以显示图标的ListCell绘制器 */
        public class IconListItemRenderer extends JLabel implements ListCellRenderer
        {
            private Border
                selectedBorder = BorderFactory.createLineBorder(Color.blue,1),
                emptyBorder = BorderFactory.createEmptyBorder(1,1,1,1);

            public Component getListCellRendererComponent(
                        JList list,
                        Object value,
                        int index,
                        boolean isSelected,
                        boolean cellHasFocus)
                {

                IconListItem item = (IconListItem)value;
                this.setIcon(item.getIcon());
                this.setText(item.getText());

                if ( isSelected ) setBorder (selectedBorder);
                else setBorder(emptyBorder);
                return this;
            }
        }
大家看到，getListCellRendererComponent方法会传入几个参数,我们就用它传入的几个参数设置JLabel的外观:图标与文字。在这个类中，我们用一个IconListItem接收调用者传过来的value,
        IconListItem item = (IconListItem) value;
IconListItem是我另外定义好的一个类，它用来存放每一个List Item的值,
        import javax.swing.*;
        public class IconListItem
        {
            Icon icon;
            String text;
            public IconListItem(Icon icon, String text)
            {
                this.icon = icon;
                this.text = text;
            }
            public Icon getIcon() { return icon;}
            public String getText() { return text;}
            public void setIcon(Icon icon){ this.icon = icon;}
            public void setText(String text){ this.text = text; }
        }
这样的话，我就可以用getIcon()和getText()方法取得每个List Item的值了,
        IconListItem item = (IconListItem) value;
        this.setIcon(item.getIcon());
        this.setText(item.getText());

至此，我们就可以用以下方法方便的更换JList的外观了,
        JList list = new JList();
        list.setCellRenderer(new IconListItemRenderer()); file://安装我们自订的cellRenderer
        DefaultListModel listModel = new DefaultListModel();
        list.setModel(listModel);
        IconListItem item = new IconListItem(new ImageIcon(...),"John");
        listModel.addElement(item);    // 为List增加Item
        ...
由于JComboBox也有一个下拉式清单，所以它的清单也是用ListCellRenderer来绘制的，所以我们也可以将这个IconListItemRenderer给它用:
        JComboBox list = new JComboBox();
        list.setRenderer(new IconListItemRenderer()); //装我们自订的cellRenderer
        DefaultComboBoxModel comboModel = new DefaultComboBoxModel();
        list.setModel(comboModel);
        IconListItem item = new IconListItem(new ImageIcon(...),"John");
        comboModel.addElement(item);    // 为List增加Item
        ...
注意，JComboBox安装绘制器时是用setRenderer()方法，JList是用setCellRenderer()方法，名字稍有不同.

以上大家看到的是可显示一个图标的List, 下面我们再看一个可显示CheckBox的List是如何实现的,以下是例图:

代码实现:
        import javax.swing.*;
        import java.awt.*;
        import javax.swing.border.*;
        import java.awt.event.*;
        /* 可以显示CheckBox的ListCell绘制器 */
        public class CheckListItemRenderer extends JCheckBox implements ListCellRenderer
        {
            public Component getListCellRendererComponent(
                        JList list,
                        Object value,
                        int index,
                        boolean isSelected,
                        boolean cellHasFocus)
            {
                CheckListItem item = (CheckListItem)value;
                this.setSelected(item.getCheck());
                this.setText(item.getText());
                this.setFont(list.getFont());
                this.setEnabled(list.isEnabled());
                return this;
            }
        }
同样这个绘制器中用一个CheckListItem存放每个List Item的值:
        public class CheckListItem
        {
            boolean check;
            String text;
            public CheckListItem(boolean check, String text)
            {
                this.check = check;
                this.text = text;
            }
            public boolean getCheck() { return check; }
            public void setCheck(boolean _check) { check = _check; }
            public String getText() { return text; }
            public void setText(String _text) { text = _text; }
        }
这个绘制器的用法同IconListItemRenderer一样，不多讲了.

三、让自订的绘制器响就鼠标事件
使用以上的CheckListItemRenderer时，大家会发现，虽然List中可以显示CheckBox了，但是用鼠标点击时，没有反应! 现在我就来解决这个问题.要澄清的是，ListCellRenderer本身是只返回一个组件用来绘制一个单元格，不能对用户动作作出反应。为些我们必须在JList上下功夫.JList有一个addMouseListener（）方法可以为自身安装一个鼠标监听器，在这里，我实现了一个MouseAdapter,并让它对mousePressed作出响应:
        class CheckListMouseListener extends MouseAdapter
        {
              public void mousePressed(MouseEvent e) {
                JList list = (JList) e.getSource();
                int index = list.locationToIndex(e.getPoint());
                CheckListItem item = (CheckListItem)list.getModel().getElementAt(index);
                item.setCheck(! item.getCheck());
                Rectangle rect = list.getCellBounds(index, index);
                list.repaint(rect);
            }
        }
使用时, 用addMouseListener(new CheckListMouseListener())就行了.

除了包含CheckBox的JList外，许多情况下，我们需要为自制的绘制器加上动作响应，如我们要实现一个可编辑的JList,　除了要扩展JTextField及实现ListCellRenderer之外，还要写一个鼠标监听器和键盘监听器，当双击时，JList变成可编辑状态，当回车时，还原成不可编辑状态

public class Datetime {

 public String getDatetime_String1() {
  String datetime = new Date().toString();
  return datetime;
 }

 public String getDatetime_String2() {
  String datetime = new Date().toGMTString();
  return datetime;
 }

 public String getDatetime_System() {
  DateFormat dt = DateFormat.getInstance();
  String datetime = dt.format(new Date()).toString();
  return datetime;
 }

 public String getDatetime_China() {
  DateFormat datetime1 = DateFormat.getDateInstance(DateFormat.LONG,
    Locale.CHINA);
  DateFormat datetime2 = DateFormat.getTimeInstance(DateFormat.LONG,
    Locale.CHINA);
  String datetime = datetime1.format(new Date()) + " "
    + datetime2.format(new Date());
  return datetime;
 }

 public String getDatetime_Standard() {
  Calendar now = Calendar.getInstance();
  String datetime = now.get(Calendar.YEAR) + "-"
    + (now.get(Calendar.MONTH) + 1) + "-"
    + now.get(Calendar.DAY_OF_MONTH) + " " + now.get(Calendar.HOUR)
    + ":" + now.get(Calendar.MINUTE) + ":"
    + now.get(Calendar.SECOND) + now.get(Calendar.MILLISECOND);
  return datetime;
 }

 public String getDatetime() {
  String datetime = new Date().toLocaleString();
  return datetime;
 }

 public String getDatetime_SimpleDateFormat() {
  try {
   SimpleDateFormat f = new java.text.SimpleDateFormat("yyyy-MM-dd");
   String sDate = f.format(new java.util.Date());
   java.util.Date dt = f.parse(sDate);
   java.sql.Date sqlDate = new java.sql.Date(dt.getTime());
   String datetime = sqlDate.toString();
   return datetime;
  } catch (Exception ee) {
   ee.printStackTrace();
   return null;
  }
 }

 public static void main(String[] args) {
  // TODO 自动生成方法存根
  System.out.println("以字符串格式显示日期时间: "
    + new Datetime().getDatetime_String1());
  System.out.println("以字符串格式显示日期时间: "
    + new Datetime().getDatetime_String2());
  System.out.println("以系统格式显示日期时间: "
    + new Datetime().getDatetime_System());
  System.out
    .println("以中国格式显示日期时间: " + new Datetime().getDatetime_China());
  System.out.println("以常用格式显示日期时间: "
    + new Datetime().getDatetime_Standard());
  System.out.println("以常用格式显示日期时间: " + new Datetime().getDatetime());
  System.out.println("以简单系统格式显示日期: "
    + new Datetime().getDatetime_SimpleDateFormat());
 }

}

/*
 JTree的构造函数:
 JTree()
 JTree(Hashtable value)
 JTree(Object[] value)//只有这个构造函数可以创建多个根结点
 JTree(TreeModel newModel)
 JTree(TreeNode root)
 JTree(TreeNode root, boolean asksAllowsChildren)
 JTree(Vector value)

 */
public class JTreeDemo {
 public static void main(String[] args) {

  // 构造函数：JTree()
  JTree example1 = new JTree();

  // 构造函数：JTree(Object[] value)
  Object[] letters = { " a ", " b ", " c ", " d ", " e " };
  JTree example2 = new JTree(letters);

  // 构造函数：JTree(TreeNode root)(TreeNode空)
  // 用空结点创建树
  DefaultMutableTreeNode node1 = new DefaultMutableTreeNode(); // 定义树结点
  JTree example3 = new JTree(node1); // 用此树结点做参数调用 JTree的构造函数创建含有一个根结点的树

  // 构造函数：JTree(TreeNode root)(同上,只是TreeNode非空)
  // 用一个根结点创建树
  DefaultMutableTreeNode node2 = new DefaultMutableTreeNode(" Color ");
  JTree example4 = new JTree(node2); // 结点不可以颜色,默认为白面黑字
  example4.setBackground(Color.lightGray);

  // 构造函数：JTree(TreeNode root, boolean
  // asksAllowsChildren)(同上,只是TreeNode又有不同)
  // 使用DefaultMutableTreeNode类先用一个根结点创建树，设置为可添加孩子结点,再添加孩子结点
  DefaultMutableTreeNode color = new DefaultMutableTreeNode(" Color ",
    true);
  DefaultMutableTreeNode gray = new DefaultMutableTreeNode(" Gray ");
  color.add(gray);
  color.add(new DefaultMutableTreeNode(" Red "));
  gray.add(new DefaultMutableTreeNode(" Lightgray "));
  gray.add(new DefaultMutableTreeNode(" Darkgray "));
  color.add(new DefaultMutableTreeNode(" Green "));
  JTree example5 = new JTree(color);

  // 构造函数：JTree(TreeNode root)(同上,只是TreeNode非空)
  // 通过逐个添加结点创建树
  DefaultMutableTreeNode biology = new DefaultMutableTreeNode(" Biology ");
  DefaultMutableTreeNode animal = new DefaultMutableTreeNode(" Animal ");
  DefaultMutableTreeNode mammal = new DefaultMutableTreeNode(" Mammal ");
  DefaultMutableTreeNode horse = new DefaultMutableTreeNode(" Horse ");
  mammal.add(horse);
  animal.add(mammal);
  biology.add(animal);
  JTree example6 = new JTree(biology);
  horse.isLeaf();
  horse.isRoot();

  // 构造函数:JTree(TreeModel newModel)
  // 用DefaultMutableTreeNodel类定义一个结点再用这个结点做参数定义一个用DefaultTreeMode
  // 创建一个树的模型,再用JTree的构造函数创建一个树

  DefaultMutableTreeNode root = new DefaultMutableTreeNode(" Root1 ");
  DefaultMutableTreeNode child1 = new DefaultMutableTreeNode(" Child1 ");
  DefaultMutableTreeNode child11 = new DefaultMutableTreeNode(" Child11 ");
  DefaultMutableTreeNode child111 = new DefaultMutableTreeNode(
    " Child111 ");
  root.add(child1);
  child1.add(child11);
  child11.add(child111);

  DefaultTreeModel model = new DefaultTreeModel(root);

  JTree example7 = new JTree(model);

  JPanel panel = new JPanel();
  panel.setLayout(new BoxLayout(panel, BoxLayout.X_AXIS));
  panel.setPreferredSize(new Dimension(700, 400));
  panel.add(new JScrollPane(example1)); // JTree必须放在JScrollPane上
  panel.add(new JScrollPane(example2));
  panel.add(new JScrollPane(example3));
  panel.add(new JScrollPane(example4));
  panel.add(new JScrollPane(example5));
  panel.add(new JScrollPane(example6));
  panel.add(new JScrollPane(example7));

  JFrame frame = new JFrame(" JTreeDemo ");
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.setContentPane(panel);
  frame.pack();
  frame.show();
 }
}

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);
        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 = getClass().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 = getClass().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 dispatch 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.");
            }
        }

        //Create and set up the window.
        JFrame frame = new JFrame("TreeDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Add content to the window.
        frame.add(new TreeDemo());

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event dispatch thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}