设计模式学习笔记十五：命令模式

介绍

命令模式，Command模式，属于对象行为模式。将“请求”封装成对象，以便使用不同的请求、队列或者日志来参数化其他对象。命令模式也支持可撤消的操作。

UML结构图：

场景模拟

本例是模拟实现一个遥控器。

代码实现

1.先模拟两个真正干活的对象，即invoker：

public class Light{
    public void on() {
        System.out.println("light is on");
    }
    public void off() {
        System.out.println("light is off");
    }
}

public class TV {
    public void on() {
        System.out.println("TV is on");
    }
    public void off() {
        System.out.println("TV is off");
    }
}

2.定义统一命令调用接口，即Command（刚开始用Runnable来着，偷懒:]）：

public interface Command {
    public void execute();
}

3.定义开关命令，统一实现Command接口，即ConcreteCommand:

public class LightOnCommand implements Command {
    private Light light;
    public LightOnCommand(Light light) {
        this.light = light;
    }
    @Override
    public void execute() {
        light.on();
    }
}

public class LightOffCommand implements Command {
    private Light light;
    public LightOffCommand(Light light) {
        this.light = light;
    }
    @Override
    public void execute() {
        light.off();
    }
}

4.定义操作控制对象，即Receiver：

public class RemoteControl {
    Command[] onCommands;
    Command[] offCommands;
    public RemoteControl() {
        onCommands = new Command[2];
        offCommands = new Command[2];
    }
    public void setOnCommand(int slot, Command onCommand, Command offCommand) {
        onCommands[slot] = onCommand;
        offCommands[slot] = offCommand;
    }
    public void onButtonWasPushed(int slot) {
        onCommands[slot].execute();
    }
    public void offButtonWasPushed(int slot) {
        offCommands[slot].execute();
    }

}

5.调用，即Client：

public class RemoteLoader {
    public static void main(String[] args) {
        RemoteControl control = new RemoteControl();
        Light light = new Light();
        TV tv = new TV();

        // 加载命令
        control.setOnCommand(0, new LightOnCommand(light), new LightOffCommand(light));
        control.setOnCommand(1, new TVOnCommand(tv), new TVOffCommand(tv));

        // 执行命令
        control.onButtonWasPushed(0);
        control.offButtonWasPushed(0);

        System.out.println();

        control.onButtonWasPushed(1);
        control.offButtonWasPushed(1);
    }
}