undoableeditdemo.java

《java事件处理指南》一书的代码,好东西

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.event.*;
import javax.swing.undo.*;

public class UndoableEditDemo extends JFrame 
                       implements UndoableEditListener, ActionListener
{
   private JTextArea jta;
   protected UndoManager undoManager;
   private JTextField jtf;
   private JMenuBar menuBar;
   private JMenu menu;
   private JMenuItem undoItem, redoItem;

   public UndoableEditDemo() 
   {
/*  An UndoManager is created to manage undo and redo operations.   */

      undoManager = new UndoManager();

/*  A JTextArea is created and placed on a JFrame.  The Document  */
/*  associated with the JTextArea is obtained.  The Document      */
/*  registers an UndoableEventListener.                           */

      jta = new JTextArea(5,15);
      jta.setLineWrap(true);
      jta.setWrapStyleWord(true);
      jta.getDocument().addUndoableEditListener(this);

      jtf = new JTextField(15);
      jtf.setEditable(false);

/*  An "Edit" menu is created with "undo" and "redo" menu items.   */
/*  These menu items will initiate undo and redo actions to the    */
/*  text in the text area. The menu items are initially disabled   */
/*  since there is initially no text in the JTextArea.             */

      undoItem = new JMenuItem("undo");
      undoItem.setEnabled(false);
      undoItem.addActionListener(this);

      redoItem = new JMenuItem("redo");
      redoItem.setEnabled(false);
      redoItem.addActionListener(this);

      menu = new JMenu("Edit");
      menu.add(undoItem);
      menu.add(redoItem);

      menuBar = new JMenuBar();
      menuBar.add(menu);

      getContentPane().add(new JScrollPane(jta), BorderLayout.CENTER);
      getContentPane().add(menuBar, BorderLayout.NORTH);
      getContentPane().add(jtf, BorderLayout.SOUTH);

      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setBounds(100, 100, 300, 250);
      setVisible(true);
   }

/*  The UndoableEditDemo class serves as the UndoableEditListener,      */
/*  so it provides an implementation of the undoableEditHappened()      */
/*  method.  When the user executes an undoable edit in the text        */
/*  area, an UndoableEditEvent is generated and sent to this method.    */
/*  The method adds the edit to the list managed by the UndoManager.    */
/*  The "undo" and "redo" menu items are enabled or disabled depending  */
/*  on whether subsequent undo and redo operations are possible.        */

   public void undoableEditHappened(UndoableEditEvent event)
   {
      undoManager.addEdit(event.getEdit());
      redoItem.setEnabled(undoManager.canRedo());
      undoItem.setEnabled(undoManager.canUndo());
   }

/*  The actionPerformed() method responds to the selection of the  */
/*  "undo" and "redo" menu items.  If the "undo" menu item was     */
/*  selected, the UndoManager attempts to undo the last undoable   */
/*  edit in its list.  If the "redo" menu item was chosen, the     */
/*  UndoManager tries to redo (undo the undo).  After the actions  */
/*  are taken, the menu items are enabled or disabled depending    */
/*  on whether subsequent undo and redo operations are possible.   */

   public void actionPerformed(ActionEvent event)
   {
      if ( event.getActionCommand().equals("undo") )
      {
         try
         {
            undoManager.undo();
            redoItem.setEnabled(undoManager.canRedo());
            undoItem.setEnabled(undoManager.canUndo());
         }
         catch (CannotUndoException cue) 
         {
            jtf.setText("Can't perform undo");
         }
      }
      if ( event.getActionCommand().equals("redo") )
      {
         try
         {
            undoManager.redo();
            redoItem.setEnabled(undoManager.canRedo());
            undoItem.setEnabled(undoManager.canUndo());
         }
         catch (CannotRedoException cre) 
         {
            jtf.setText("Can't perform redo");
         }
      }
   }

   public static void main(String args[]) 
   {
      UndoableEditDemo demo = new UndoableEditDemo();
   }
}