[Design Pattern] 커맨드 패턴(Command Pattern)

"헤드 퍼스트 디자인 패턴(개정판)"을 읽고 정리한 내용입니다.

6. 호출 캡슐화하기

커맨드 패턴

 커맨드 패턴(Command Pattern)은 요청을 객체로 캡슐화하여 다른 객체들을 다양한 요청에 따라 매개변수화 할 수있고, 요청을 큐에 넣거나 로그를 남기며, 실행 취소가 가능한 작업을 지원할 수 있게 한다.

 

예시

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

public class NoCommand implements Command {
	public void execute() { }
	public void undo() { }
}

---

public class Light {
	String location;

	public Light(String location) {
		this.location = location;
	}

	public void on() {
		System.out.println(location + " light is on");
	}

	public void off() {
		System.out.println(location + " light is off");
	}

}

public class LightOnCommand implements Command {

    Light light;

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

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

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

public class LightOffCommand implements Command {

    Light light;

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

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

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

---

public class RemoteControlWithUndo {
    Command[] onCommands;
    Command[] offCommands;
    Command undoCommand;

    public RemoteControlWithUndo() {
        onCommands = new Command[7];
        offCommands = new Command[7];

        Command noCommand = new NoCommand();
        for (int i = 0; i < 7; i++) {
            onCommands[i] = noCommand;
            offCommands[i] = noCommand;
        }

        undoCommand = noCommand;
    }

    public void setCommand(int slot, Command onCommand, Command offCommand) {
        onCommands[slot] = onCommand;
        offCommands[slot] = offCommand;
    }

    public void onButtonWasPushed(int slot) {
        onCommands[slot].execute();
        undoCommand = onCommands[slot];
    }

    public void offButtonWasPushed(int slot) {
        offCommands[slot].execute();
        undoCommand = offCommands[slot];
    }

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

---

public class RemoteLoader {
    public static void main(String[] args) {
        RemoteControlWithUndo remoteControlWithUndo = new RemoteControlWithUndo();

        Light livingRoomLight = new Light("Living Room");
        Light kitchenLight = new Light("Kitchen");

        LightOnCommand livingRoomLightOn = new LightOnCommand(livingRoomLight);
        LightOffCommand livingRoomLightOff = new LightOffCommand(livingRoomLight);

        LightOnCommand kitchenLightOn = new LightOnCommand(kitchenLight);
        LightOffCommand kitchenLightOff = new LightOffCommand(kitchenLight);

        remoteControlWithUndo.setCommand(0, livingRoomLightOn, livingRoomLightOff);
        remoteControlWithUndo.setCommand(1, kitchenLightOn, kitchenLightOff);

        remoteControlWithUndo.onButtonWasPushed(0);
        remoteControlWithUndo.offButtonWasPushed(0);
        remoteControlWithUndo.undoButtonWasPushed(0);

        remoteControlWithUndo.onButtonWasPushed(1);
        remoteControlWithUndo.offButtonWasPushed(1);
        remoteControlWithUndo.undoButtonWasPushed(1);
    }
}

// Output
Living Room light is on
Living Room light is off
Living Room light is on
Kitchen light is on
Kitchen light is off
Kitchen light is on