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命令模式--撤銷恢複
原文：https://abstractforever.iteye.com/blog/962219
該例子來自閻宏提供的例子程序，以畫線為例：
命令接口Command：
package com.javapatterns.command.drawlines;
//命令接口
public interface Command {
abstract public void execute();// 執行操作
abstract public void unexecute();// 取消操作
abstract public boolean canExecute();//是否允許執行操作
abstract public boolean canUnexecute();//是否允許取消操作
}
添加線命令類AddLineCommand：
/* Generated by Together */
package com.javapatterns.command.drawlines;
//添加線命令類
public class AddLineCommand implements Command {
private Drawing drawing;// 畫布
private Line line;//直線
public AddLineCommand(Drawing targetDrawing, Line newLine) {
drawing = targetDrawing;
line = newLine;
}
//執行將直線添加到畫布的操作
public void execute() {
drawing.add(line);
}
//執行將直線從畫布中移除的操作
public void unexecute() {
drawing.remove(line);
}
public boolean canExecute() {
return true;
}
public boolean canUnexecute() {
return true;
}
}
命令集合類CommandList：
package com.javapatterns.command.drawlines;
import java.util.Stack;
//命令集合類，負責存儲執行過的命令和撤銷執行的命令
public class CommandList {
private Stack<Command> executedCommands = new Stack<Command>();
private Stack<Command> unexecutedCommands = new Stack<Command>();
private void _execute(Command command) {
command.execute();//執行具體的命令
executedCommands.push(command);//記錄執行的命令
}
//執行命令
public void execute(Command command) {
unexecutedCommands.removeAllElements();
_execute(command);
}
//撤銷執行,每執行一次該方法，將從最近的一次操作開始撤銷
public void unexecute() {
Command command = (Command) executedCommands.pop();//出棧最後一次執行命令
command.unexecute();//撤銷該命令的執行
unexecutedCommands.push(command);//記錄撤銷的命令
}
//恢複執行,每執行一次該方法，將從最近的一次操作開始撤銷
public void reexecute() {
Command command = (Command) unexecutedCommands.pop();//出棧最後一次撤銷命令
_execute(command);//重新執行
}
//清空撤銷和恢複的緩存
public void reset() {
executedCommands.removeAllElements();
unexecutedCommands.removeAllElements();
}
//是否允許撤銷命令,沒有執行過命令就不存在撤銷
public boolean canUnexecuteCommand() {
return !executedCommands.empty();
}
//是否允許恢複命令,沒有撤銷過命令就不存在恢複
public boolean canReexecuteCommand() {
return !unexecutedCommands.empty();
}
}
畫布Drawing：
/* Generated by Together */
package com.javapatterns.command.drawlines;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.Enumeration;
import java.util.Vector;
//(接收者，負責具體實施和執行一個請求)畫布，可以在該畫布上畫任意條直線
public class Drawing extends Canvas implements MouseListener,
MouseMotionListener {
private static final long serialVersionUID = -4887753465176351050L;
private SimpleDraw applet;//應用程序
private Vector<Line> lines;//線集合
private Point startPosition;//畫線開始位置
private Point mousePosition;//鼠標位置
private boolean mousePressed;//鼠標是否按下
//構造方法，初始化屬性信息
public Drawing(SimpleDraw owner) {
applet = owner;
lines = new Vector<Line>();
mousePressed = false;//默認鼠標未按下
setBackground(Color.GREEN);//設置畫布背景色
addMouseListener(this);//添加鼠標監聽器,自己實現了該接口
addMouseMotionListener(this);//添加鼠標移動事件的偵聽器，自己實現了該接口
}
//添加一條線（行動方法）
public void add(Line line) {
lines.addElement(line);
repaint();
}
//刪除一條線（行動方法）
public void remove(Line line) {
lines.removeElement(line);
repaint();
}
public void paint(Graphics graphics) {
Enumeration<Line> enumeration = lines.elements();
Line currentLine;
while (enumeration.hasMoreElements()) {
currentLine = (Line) (enumeration.nextElement());
currentLine.paint(graphics);
}
if (mousePressed) {
graphics.drawLine(startPosition.x, startPosition.y,
mousePosition.x, mousePosition.y);
}
}
//鼠標按鍵在組件上單擊（按下並釋放）時調用
public void mouseClicked(MouseEvent event) {
}
//鼠標進入到組件上時調用
public void mouseEntered(MouseEvent event) {
}
//鼠標離開組件時調用
public void mouseExited(MouseEvent event) {
}
//鼠標按鍵在組件上按下時調用
public void mousePressed(MouseEvent event) {
mousePressed = true;//設置鼠標為按下狀態
startPosition = event.getPoint();//記錄直線的開始位置
}
//鼠標按鈕在組件上釋放時調用
public void mouseReleased(MouseEvent event) {
if (!event.getPoint().equals(startPosition)) {//兩點不重合
Line line = new Line(startPosition, event.getPoint());//創建直線
AddLineCommand command = new AddLineCommand(this, line);//創建添加直線的一個命令
applet.execute(command);//請求者請求命令的執行
}
mousePressed = false;
}
public void mouseDragged(MouseEvent event) {
mousePosition = event.getPoint();
repaint();
}
public void mouseMoved(MouseEvent event) {
}
}
直線Line：
package com.javapatterns.command.drawlines;
import java.awt.Point;
import java.awt.Graphics;
public class Line {
private Point start;
private Point end;
public Line( Point startPos, Point endPos ) {
start = startPos;
end = endPos;
}
public void paint( Graphics graphics ) {
graphics.drawLine( start.x, start.y, end.x, end.y );
}
}
容器SimpleDraw：
/* Generated by Together */
package com.javapatterns.command.drawlines;
import java.applet.Applet;
import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Panel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
// 請求者(負責調用命令對象執行請求)
public class SimpleDraw extends Applet implements ActionListener {
private static final long serialVersionUID = 2317696438230972428L;
private Drawing drawing;// 畫布
private CommandList commands;// 命令集合
private Button undoButton;// 撤銷按鈕
private Button redoButton;// 恢複按鈕
private Button resetButton;// 清空撤銷和恢複按鈕
public void init() {
Panel panel = new Panel();// 麵板
commands = new CommandList();// 初始化命令集合
setLayout(new BorderLayout());// 設置布局
drawing = new Drawing(this);// 初始化畫布
add("Center", drawing);
undoButton = new Button("撤銷");// 初始化撤銷按鈕
redoButton = new Button("恢複");// 初始化恢複按鈕
resetButton = new Button("重置");
undoButton.addActionListener(this);// 添加按鈕監聽器
redoButton.addActionListener(this);// 添加按鈕監聽器
resetButton.addActionListener(this);// 添加按鈕監聽器
panel.add(undoButton);
panel.add(redoButton);
panel.add(resetButton);
add("South", panel);
updateButtons();// 初始化按鈕狀態
}
public void execute(Command command) {
commands.execute(command);// 執行命令
updateButtons();
}
// 更新按鈕狀態(根據是否能夠undo撤銷或者是否能夠redo恢複)
private void updateButtons() {
undoButton.setEnabled(commands.canUnexecuteCommand());
redoButton.setEnabled(commands.canReexecuteCommand());
}
// 當點擊撤銷按鈕或者恢複按鈕時出發該方法執行
public void actionPerformed(ActionEvent event) {
if (event.getSource() == undoButton) {
commands.unexecute();
updateButtons();
}else if (event.getSource() == redoButton) {
commands.reexecute();
updateButtons();
}else if (event.getSource() == resetButton) {
commands.reset();
updateButtons();
}
}
}
實例下載：
https://download.csdn.net/detail/yang_hui1986527/3840789
最後更新：2017-04-02 06:52:11