一、前言：

命令模式的注意事项和细节：

1. 将发起请求的对象与执行请求的对象解耦。
2. 发起请求的对象就是调用者，调用者只需调用命令对象的 execute() 方法就可以让接受者工作，而不必知道接受者具体是如何实现的。
3. 容易设计一个命令队列，只要把命令对象放入队列，就可以多线程的执行命令。
4. 容易实现对请求的撤销与重做。

二、命令模式：

2.1、UML 图：

2.2、代码实例：

Step 1) 创建 Command 接口：

public interface Command {
    
    
    public void execute();
    public void undo();
}

Step 2) 创建 LightOnCommand 实现类：

public class LightOnCommand implements Command{
    
    

    LightReceive light;

    public LightOnCommand(LightReceive light) {
    
    
        this.light = light;
    }

    @Override
    public void execute() {
    
    
        light.on();
    }

    @Override
    public void undo() {
    
    
        light.off();
    }
}

Step 3) 创建 LightOffCommand 实现类：

public class LightOffCommand implements Command{
    
    

    LightReceive light;

    public LightOffCommand(LightReceive light) {
    
    
        this.light = light;
    }

    @Override
    public void execute() {
    
    
        light.off();
    }

    @Override
    public void undo() {
    
    
        light.on();
    }
}

Step 4) 创建 NoCommand 实现类：

public class NoCommand implements Command{
    
    
    @Override
    public void execute() {
    
    

    }

    @Override
    public void undo() {
    
    

    }
}

Step 5) 创建 RemoteController 类：

public class RemoteController {
    
    
    Command[] onCommands;
    Command[] offCommands;

    Command undoCommand;

    public RemoteController(){
    
    
        onCommands = new Command[5];
        offCommands = new Command[5];

        for(int i=0; i<5; i++){
    
    
            onCommands[i] = new NoCommand();
            offCommands[i] = new NoCommand();
        }
    }

    public void setCommand(int no, Command onCommand, Command offCommand){
    
    
        onCommands[no] = onCommand;
        offCommands[no] = offCommand;
    }

    public void onButtonWasPushed(int no){
    
    
        onCommands[no].execute();
        undoCommand = onCommands[no];
    }

    public void offButtonWasPushed(int no){
    
    
        offCommands[no].execute();
        undoCommand = offCommands[no];
    }

    public void undoButtonWasPushed(){
    
    
        undoCommand.undo();
    }
}

Step 6) 创建 LightReceive 类：

public class LightReceive {
    
    
    public void on(){
    
    
        System.out.println("点灯打开了！");
    }

    public void off(){
    
    
        System.out.println("点灯关闭了！");
    }
}

Step 7) 创建 main 方法：

public class Client {
    
    
    public static void main(String[] args) {
    
    
        LightReceive lightReceive = new LightReceive();

        LightOnCommand lightOnCommand = new LightOnCommand(lightReceive);
        LightOffCommand lightOffCommand = new LightOffCommand(lightReceive);

        RemoteController remoteController = new RemoteController();
        remoteController.setCommand(0, lightOnCommand, lightOffCommand);

        System.out.println("---------------按下灯的开按钮-----------------");
        remoteController.onButtonWasPushed(0);

        System.out.println("---------------按下灯的关按钮-----------------");
        remoteController.offButtonWasPushed(0);

        System.out.println("---------------按下撤销按钮-----------------");
        remoteController.undoButtonWasPushed();
    }
}

• 由 ChiKong_Tam 写于 2020 年 10 月 20 日