python

       上篇介绍了命令模式的理论知识，这里再写两个小例子，加深理解。

     1、撤销命令，关键在于命令执行的时侯保存这个命令对象，这就是把操作封装成对象的好处。

//这个不变
public class Light {
public void off(){
System.out.println("off...");
}
public void on(){
System.out.println("on...");
}
}

//Command接口添加一个undo()
public interface Command {
public void execute();
public void undo();
}
public class LightOffCommand implements Command {
Light light;
public LightOffCommand(Light light){
this.light = light;
}

public void execute() {
light.off();
}
//在这里进行之前操作的逆操作，实现“撤销”
public void undo(){
light.on();
}
}
public class LightOnCommand implements Command {
Light light;
public LightOnCommand(Light light){
this.light = light;
}
public void execute() {
light.on();
}

public void undo(){
light.off();
}
}
public class RemoteControl {
Command c;
Command lastCommand;
public void setCommand(Command c){
this.c = c;
}
public void pressButton(){
c.execute();
//保存命令对象的引用
 lastCommand = c;
}
public void undoPressButton(){
lastCommand.undo();
}
}

      测试:

public class CommandLoader {
public static void main(String[] args) {
RemoteControl src = new RemoteControl();
Light light = new Light();
LightOnCommand lo = new LightOnCommand(light);
src.setCommand(lo);
//操作
src.pressButton();
System.out.println();
//撤销操作
src.undoPressButton();
}
}

      输出:

on...
off...

      这里模拟的是简单操作，实际上可能有针对Light状态值的操作，但实现原理是一样的。

     2、宏命令：创建一个新类MacroCommand，封装多个命令，达到一次性执行多个命令的目的。

//此类与一般的具体命令是一个级别的
public class MacroCommand implements Command{
//保存多个命令对象
Command[] commands;

public MacroCommand(Command[] commands) {
this.commands = commands;
}

public void execute(){
for (Command c : commands) {
c.execute();
}
}
}

public class CommandLoader {
public static void main(String[] args) {
 //遥控器
RemoteControl rc = new RemoteControl();
//三个命令
LightOnCommand lo = new LightOnCommand(new Light());
TvOnCommand to = new TvOnCommand(new Tv());
AirConditionOnCommand ao = new AirConditionOnCommand(new AirCondition());

Command[] cs = {lo,to,ao};
//宏命令
 MacroCommand mc = new MacroCommand(cs);

rc.setCommand(mc);
rc.pressButton();
}
}

       执行结果是：

on...
tv on...
air condition on...