🇺🇸

State Pattern

💡

상태를 객체로 나타내기

Intent

State is a behavioral design pattern that lets an object alter its behavior when its internal state changes. It appears as if the object changed its class.

Implementation

Applicablity

Code Examples


package oodesign.design.behavioral.state;

public class Light {

    protected LightState onState = new OnState();
    protected LightState offState = new OffState();

    protected LightState lightState;

    public Light() {
        this.lightState = new OffState();
    }

    public void on(){
        lightState.on();
    }

    public void off(){
        lightState.off();
    }

    interface LightState {
        void on();
        void off();
    }

    class OnState implements LightState{

        @Override
        public void on() {
            System.out.println("nothing");
        }

        @Override
        public void off() {
            System.out.println("on -> off");
            lightState = offState;
        }
    }

    class OffState implements LightState{

        @Override
        public void on() {
            System.out.println("off -> on");
            lightState = onState;
        }

        @Override
        public void off() {
            System.out.println("Nothing");
        }
    }
}


package oodesign.design.behavioral.state;

public class Main {

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

        light.off();
        light.off();
        light.off();

        light.on();
        light.on();
        light.on();

        light.off();
    }
}


Nothing
Nothing
Nothing
off -> on
nothing
nothing
on -> off

Process finished with exit code 0

Note

상태 패턴은 전략 패턴과 UML이 동일함

Intent 가 다름

전략패턴의 execute - 알고리즘의 실행
전략패턴의 action - 상태의 변경