ctrl+z的JAVA实现，借助了命令模式（command pattern）
前些天学习<<JAVA与模式>>，到命令模式时，随带给了一个CTRL+Z案例的实现，想来学习编程这么久，CTRL+Z还没有认真实现过。
因此，借助JAVA与模式里面的源代码，自己对撤销和回退进行了实现（JAVA与模式书中代码有部分问题）。此次用到了命令模式，因为有界面，有按钮，有接收者，有发送者。
以下是类图，只为方便，未考虑UML细节规范。
以下是程序的实现。
MainFrame类：提供Main方法，Client类：类似于看电视的人，这里关联了UndoableTextArea，ItsukyuQuatation是因为要初始化该对象
package undoRedo;
import java.awt.Frame;
import java.awt.event.*;
public class MainFrame extends Frame {
private static UndoableTextArea text;
private static ItsukyuQuatation panel;
public MainFrame(String title)
{
super(title);
}
public static void main(String[] args)
{
//构造可撤消的textArea
text = new UndoableTextArea("Your text here");
//构造panel
panel = new ItsukyuQuatation(text);
//构造frame
MainFrame frame = new MainFrame("测试undo和redo");
//增加窗体关闭事件
frame.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
});
frame.add(panel);
frame.setSize(300,300);
frame.setVisible(true);
}
}
ItsukyuQuatation类：面板类，里面包括undo和redo两个按钮，类似于命令模式中的摇控器。实现了ActionListener接口。
package undoRedo;
import java.awt.BorderLayout;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class ItsukyuQuatation extends Panel implements ActionListener {
private final Command undo;
private final Command redo;
public ItsukyuQuatation(UndoableTextArea text)
{
this.setLayout(new BorderLayout());
Panel toolbar = new Panel();
undo = new UndoCommand(text);
redo = new RedoCommand(text);
undo.addActionListener(this);
redo.addActionListener(this);
toolbar.add(undo);
toolbar.add(redo);
this.add(toolbar,"North");
this.add(text,"Center");
}
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
Command cmd = (Command)e.getSource();
cmd.execute();
}
}
UndoableTextArea类：类似于命令模式中的电视机类。实现了StateEditable接口，因此该类具有可撤销和重做的功能。重载的storeState和restoreState即是把文本中的内容放到hashTable里去。
该类是最核心的类，实现ctrl+z的原理简单说就是UndoManger.edits是一个Vector动态数组，对每次的按键动作，都会存储一份当前的文本内容到数据。当点击undo按钮，
数组索引（UnoManager类的indexOfNextAdd变量）前移一位，取得前一状态的文本内容。点击redo按钮，数组索引后移一位，取后一状态的文本内容。但是各状态内容均未删或修改。
initUndoable()方法，如果用keyPressed事件，那么最近的状态未加到undoManager.edits列里。因此选用keyReleased事件。如果监听valueChanged事件，那么代码就
和JAVA与模式一书中一样，只能实现最近一次的编辑撤消。
package undoRedo;
import java.awt.TextArea;
import java.awt.event.*;
import java.util.Hashtable;
import javax.swing.undo.*;
import javax.swing.undo.StateEditable;
public class UndoableTextArea extends TextArea implements StateEditable {
private UndoManager undoManager;
private final static String KEY_STATE="UndoableTextAreaKey";
private StateEdit currentEdit;
boolean textChanged = false;
public UndoableTextArea()
{
super();
initUndoable();
}
public UndoableTextArea(String string)
{
super(string);
initUndoable();
}
//存储状态
public void storeState(Hashtable<Object, Object> hashTable) {
// TODO Auto-generated method stub
hashTable.put(KEY_STATE, this.getText());
}
//还原状态
public void restoreState(Hashtable<?, ?> hashTable) {
// TODO Auto-generated method stub
Object data = hashTable.get(KEY_STATE);
if(data!=null)
{
this.setText((String)data);
}
}
//撤销方法
public boolean undo()
{
try
{
undoManager.undo();
System.out.println("undo=" + undoManager.toString());
return true;
}catch(CannotUndoException e)
{
System.out.println("Can't undo");
}
return false;
}
//重做方法
public boolean redo()
{
try
{
undoManager.redo();
System.out.println("redo=" + undoManager.toString());
return true;
}catch(CannotRedoException e)
{
System.out.println("Can't redo");
}
return false;
}
private void initUndoable()
{
this.undoManager = new UndoManager();
this.currentEdit = new StateEdit(this);
this.addKeyListener(new KeyAdapter()
{
/*
*
* 如果用keyPressed事件，那么最近的状态未加到undoManager.edits列里。
* 因此选用keyReleased事件。
*
public void keyPressed(KeyEvent event)
{
if(event.isActionKey())
{
//takeSnapshot();
}else
{
textChanged = true;
takeSnapshot();
}
}
*/
public void keyReleased(KeyEvent event)
{
if(event.isActionKey())
{
//takeSnapshot();
}else
{
textChanged = true;
takeSnapshot();
}
}
});
this.addFocusListener(new FocusAdapter()
{
public void focusLost(FocusEvent event)
{
//takeSnapshot();
}
});
}
private void takeSnapshot()
{
if(textChanged)
{
this.currentEdit.end();
this.undoManager.addEdit(this.currentEdit);
this.currentEdit = new StateEdit(this);
System.out.println("takeSnapshot=" + undoManager.toString());
textChanged = false;
}
}
}
Command抽象类：定义按钮，抽象方法 execute()
UndoCommand,RedoCommand均是Command类的实现，类似于命令模式中的具体按钮，调用接收者的方法进行实现。
package undoRedo;
import java.awt.Button;
public abstract class Command extends Button {
public Command(String caption)
{
super(caption);
}
public abstract void execute();
}
package undoRedo;
public class UndoCommand extends Command {
UndoableTextArea text;
public UndoCommand(UndoableTextArea text)
{
super("Undo");
this.text = text;
}
@Override
public void execute() {
// TODO Auto-generated method stub
text.undo();
}
}
package undoRedo;
public class RedoCommand extends Command {
UndoableTextArea text;
public RedoCommand(UndoableTextArea text)
{
super("Redo");
this.text = text;
}
@Override
public void execute() {
// TODO Auto-generated method stub
text.redo();
}
}
