《Java2图形设计卷II：Swing》配套光盘源码

				import java.awt.*;
				import java.awt.event.*;
				import javax.swing.*;
				import javax.swing.event.*;
				import javax.swing.text.*;
				import javax.swing.undo.*;
				
				public class Test extends JApplet {
					private JTextArea textArea = new JTextArea("some content");
					private Document document = textArea.getDocument();
					private UndoManager undoManager = new UndoManager();
					private UndoLastAction undoAction = new UndoLastAction();
					private RedoAction redoAction = new RedoAction();
				
					public Test() {
						Container contentPane = getContentPane();
				
						createMenu();
						contentPane.add(textArea, BorderLayout.CENTER);
				
						textArea.setFont(new Font("Dialog", Font.PLAIN, 24));
						document.addUndoableEditListener(
													  new UndoableEditListener() {
							public void undoableEditHappened(UndoableEditEvent e){
								undoManager.addEdit(e.getEdit());
								undoAction.update();
								redoAction.update();
							}
						});
					}
					private void createMenu() {
						JMenuBar menuBar = new JMenuBar();
						JMenu editMenu = new JMenu("Edit");
				
						editMenu.add(new DefaultEditorKit.CutAction());
						editMenu.add(new DefaultEditorKit.CopyAction());
						editMenu.add(new DefaultEditorKit.PasteAction());
				
						editMenu.addSeparator();
				
						editMenu.add(undoAction);
						editMenu.add(redoAction);
				
						menuBar.add(editMenu);
						setJMenuBar(menuBar);
					}
					class RedoAction extends AbstractAction {
						public RedoAction() {
							super("Redo");
							update();
						}
						public void actionPerformed(ActionEvent e) {
							undoManager.redo();
							undoAction.update();
							update();
						}
						public void update() {
							boolean canRedo = undoManager.canRedo();
				
							if(canRedo) {
								setEnabled(true);
								putValue(Action.NAME, 
										 undoManager.getRedoPresentationName());
							}
							else {
								setEnabled(false);
								putValue(Action.NAME, "Redo");
							}
						}
					}
					class UndoLastAction extends AbstractAction {
						public UndoLastAction() {
							super("Undo");
							update();
						}
						public void actionPerformed(ActionEvent e) {
							undoManager.undo();
							redoAction.update();
							update();
						}
						public void update() {
							boolean canUndo = undoManager.canUndo();
				
							if(canUndo) {
								setEnabled(true);
								putValue(Action.NAME, 
										 undoManager.getUndoPresentationName());
							}
							else {
								setEnabled(false);
								putValue(Action.NAME, "Undo");
							}
						}
					}
				}