Design Patterns - Command

요청을 캡슐화 하여 호출자(Invoker)와 수신자(receiver)를 분리하는 패턴

요청을 처리하는 방법이 바뀌더라도 호출자의 코드는 변경되지 않는다

public interface Command {

    void execute();

    void undo();

}

public class GameStartCommand implements Command {

    private Game game;

    public GameStartCommand(Game game) {
        this.game = game;
    }

    @Override
    public void execute() {
        game.start();
    }

    @Override
    public void undo() {
        new GameEndCommand(this.game).execute();
    }
}

public class GameEndCommand implements Command {

    private Game game;

    public GameEndCommand(Game game) {
        this.game = game;
    }

    @Override
    public void execute() {
        game.end();
    }

    @Override
    public void undo() {
        new GameStartCommand(this.game).execute();
    }
}

public class LightOffCommand implements Command {

    private Light light;

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

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

    @Override
    public void undo() {
        new LightOnCommand(this.light).execute();
    }
}

public class LightOnCommand implements Command {

    private Light light;

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

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

    @Override
    public void undo() {
        new LightOffCommand(this.light).execute();
    }
}

public class Button {

    private Stack<Command> commands = new Stack<>();

    public void press(Command command) {
        command.execute();
        commands.push(command);
    }

    public void undo() {
        if (!commands.isEmpty()) {
            Command command = commands.pop();
            command.undo();
        }
    }

    public static void main(String[] args) {
        Button button = new Button();
        button.press(new GameStartCommand(new Game()));
        button.press(new LightOnCommand(new Light()));
        button.undo();
        button.undo();
    }

}

public class MyApp {

    private Command command;

    public MyApp(Command command) {
        this.command = command;
    }

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

    public static void main(String[] args) {
        MyApp myApp = new MyApp(new GameStartCommand(new Game()));
    }
}

• 장점
  • 기존 코드를 변경하지 않고 새로운 커맨드를 만들 수 있다
  • 수신자의 코드가 변경되어도 호출자의 코드는 변경되지 않는다
  • 커맨드 객체를 로깅, DB에 저장, 네트워크로 전송 하는 등 다양한 방법으로 활용할 수도 있다
• 단점
  • 코드가 복잡하고 클래스가 많아진다

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코딩으로 학습하는 GoF의 디자인 패턴 - 인프런 | 강의