Java 设计模式之命令模式

本文为笔者学习《Head First设计模式》的笔记，并加入笔者自己的理解和归纳总结

命令模式将“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销的操作。

结构图

遥控器（RemoteControl）通过命令（Command）控制灯的开关（Light）。

public class RemoteControl {

    private Command command;

    public void setCommand(Command command) {
        this.command = command;
    }

    public void run() {
        command.execute();
    }

    public void undo() {
        command.undo();
    }

}

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

public class Light {

    public void turnOn() {
        System.out.println("light trun on");
    }

    public void turnOff() {
        System.out.println("light trun off");
    }
}

灯的开关命令

public class LightOnCommand implements Command {

    private Light light;

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

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

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

}

public class LightOffCommand implements Command {

    private Light light;

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

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

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

}

运行

public static void main(String[] args) {
    Light light = new Light();
    RemoteControl remoteControl = new RemoteControl();

    Command command = new LightOnCommand(light);
    remoteControl.setCommand(command);
    remoteControl.run();

    command = new LightOffCommand(light);
    remoteControl.setCommand(command);
    remoteControl.run();
    remoteControl.undo();
}

输出

light trun on
light trun off
light trun on

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