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用途:
1 将一个请求封装为一个对象，实现请求的顺序控制、选择和时序控制
2 实现对请求的Undo和Redo操作
3 需要进行请求的日志操作
结构：
解说：
Client --> MainApplet
Invoker--> Button Invoker
Command --> ActionListener Execute--> actionPerformed()
ConcreteCommnand --> Command1,Command2 Execute--> actionPerformed()
Receiver --> textField1,textField2 Action--> setText()
Source:
package jdeveloper.patterns.command;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
/**
* Title: Jdeveloper's Java Projdect
* Description: n/a
* Copyright: Copyright (c) 2001
* Company: soho
* @author jdeveloper
* @version 1.0
*/
public class MainApplet extends Applet {
boolean isStandalone = false;
Button Invoker = new Button();
FlowLayout flowLayout1 = new FlowLayout();
TextField textField1 = new TextField();
TextField textField2 = new TextField();
/**Get a parameter value*/
public String getParameter(String key, String def) {
return isStandalone ? System.getProperty(key, def) :
(getParameter(key) != null ? getParameter(key) : def);
}
/**Construct the applet*/
public MainApplet() {
}
/**Initialize the applet*/
public void init() {
try {
jbInit();
}
catch(Exception e) {
e.printStackTrace();
}
}
/**Component initialization*/
private void jbInit() throws Exception {
Invoker.setLabel("Invoker");
this.setLayout(flowLayout1);
textField2.setColumns(8);
textField2.setEditable(false);
textField1.setColumns(8);
textField1.setEditable(false);
this.add(Invoker, null);
this.add(textField1, null);
this.add(textField2, null);
Command1 cmd1 = new Command1();
Command2 cmd2 = new Command2();
Invoker.addActionListener(cmd1);
Invoker.addActionListener(cmd2);
}
/**Start the applet*/
public void start() {
}
/**Stop the applet*/
public void stop() {
}
/**Destroy the applet*/
public void destroy() {
}
/**Get Applet information*/
public String getAppletInfo() {
return "Applet Information";
}
/**Get parameter info*/
public String[][] getParameterInfo() {
return null;
}
/**Main method*/
public static void main(String[] args) {
MainApplet applet = new MainApplet();
applet.isStandalone = true;
Frame frame;
frame = new Frame() {
protected void processWindowEvent(WindowEvent e) {
super.processWindowEvent(e);
if (e.getID() == WindowEvent.WINDOW_CLOSING) {
System.exit(0);
}
}
public synchronized void setTitle(String title) {
super.setTitle(title);
enableEvents(AWTEvent.WINDOW_EVENT_MASK);
}
};
frame.setTitle("Applet Frame");
frame.add(applet, BorderLayout.CENTER);
applet.init();
applet.start();
frame.setSize(400,320);
Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
frame.setLocation((d.width - frame.getSize().width) / 2, (d.height - frame.getSize().height) / 2);
frame.setVisible(true);
}
class Command1 implements ActionListener{
public void actionPerformed(ActionEvent e){
textField1.setText("Hello");
}
}
class Command2 implements ActionListener{
public void actionPerformed(ActionEvent e){
textField2.setText("World");
}
}
}
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