case study

이런 상황을 가정

• 다음과 같은 식으로 뽑기 기계 컨트롤러용 자바 코드를 구현해주세요~
  

• GumballMachine.java

package headfirst.designpatterns.state.gumball;

public class GumballMachine {
 
	final static int SOLD_OUT = 0;
	final static int NO_QUARTER = 1;
	final static int HAS_QUARTER = 2;
	final static int SOLD = 3;
 
	int state = SOLD_OUT;
	int count = 0;
  
	public GumballMachine(int count) {
		this.count = count;
		if (count > 0) {
			state = NO_QUARTER;
		}
	}
  
	public void insertQuarter() {
		if (state == HAS_QUARTER) {
			System.out.println("You can't insert another quarter");
		} else if (state == NO_QUARTER) {
			state = HAS_QUARTER;
			System.out.println("You inserted a quarter");
		} else if (state == SOLD_OUT) {
			System.out.println("You can't insert a quarter, the machine is sold out");
		} else if (state == SOLD) {
        	System.out.println("Please wait, we're already giving you a gumball");
		}
	}

	public void ejectQuarter() {
		if (state == HAS_QUARTER) {
			System.out.println("Quarter returned");
			state = NO_QUARTER;
		} else if (state == NO_QUARTER) {
			System.out.println("You haven't inserted a quarter");
		} else if (state == SOLD) {
			System.out.println("Sorry, you already turned the crank");
		} else if (state == SOLD_OUT) {
        	System.out.println("You can't eject, you haven't inserted a quarter yet");
		}
	}
 
	public void turnCrank() {
		if (state == SOLD) {
			System.out.println("Turning twice doesn't get you another gumball!");
		} else if (state == NO_QUARTER) {
			System.out.println("You turned but there's no quarter");
		} else if (state == SOLD_OUT) {
			System.out.println("You turned, but there are no gumballs");
		} else if (state == HAS_QUARTER) {
			System.out.println("You turned...");
			state = SOLD;
			dispense();
		}
	}
 
	private void dispense() {
		if (state == SOLD) {
			System.out.println("A gumball comes rolling out the slot");
			count = count - 1;
			if (count == 0) {
				System.out.println("Oops, out of gumballs!");
				state = SOLD_OUT;
			} else {
				state = NO_QUARTER;
			}
		} else if (state == NO_QUARTER) {
			System.out.println("You need to pay first");
		} else if (state == SOLD_OUT) {
			System.out.println("No gumball dispensed");
		} else if (state == HAS_QUARTER) {
			System.out.println("No gumball dispensed");
		}
	}
 
	public void refill(int numGumBalls) {
		this.count = numGumBalls;
		state = NO_QUARTER;
	}

	public String toString() {
		StringBuffer result = new StringBuffer();
		result.append("\nMighty Gumball, Inc.");
		result.append("\nJava-enabled Standing Gumball Model #2004\n");
		result.append("Inventory: " + count + " gumball");
		if (count != 1) {
			result.append("s");
		}
		result.append("\nMachine is ");
		if (state == SOLD_OUT) {
			result.append("sold out");
		} else if (state == NO_QUARTER) {
			result.append("waiting for quarter");
		} else if (state == HAS_QUARTER) {
			result.append("waiting for turn of crank");
		} else if (state == SOLD) {
			result.append("delivering a gumball");
		}
		result.append("\n");
		return result.toString();
	}
}

• GumballMachineTestDrive.java

package example.gumball;

public class GumballMachineTestDrive {

	public static void main(String[] args) {
		GumballMachine gumballMachine = new GumballMachine(5);

		System.out.println(gumballMachine);

		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();

		System.out.println(gumballMachine);

		gumballMachine.insertQuarter();
		gumballMachine.ejectQuarter();
		gumballMachine.turnCrank();

		System.out.println(gumballMachine);

		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.ejectQuarter();

		System.out.println(gumballMachine);

		gumballMachine.insertQuarter();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();
		gumballMachine.insertQuarter();
		gumballMachine.turnCrank();

		System.out.println(gumballMachine);
	}
}

수많은 if 문으로 구현완료 하지만...

요청 사항이 변경되었다...!

• 10분의 1확률로 공짜 알멩이를 받을 수 있도록 추가해주세요
  

• 기존의 소스코드로는 수정할 부분이 너무 많다.
• 좋은 방법이 없는가?

state pattern 소개

정의

객체가 특정 상태에 따라 행위를 달리하는 상황에서,
자신이 직접 상태를 체크하여 상태에 따라 행위를 호출하지 않고,
상태를 객체화 하여 상태가 행동을 할 수 있도록 위임하는 패턴

객체의 내부 상태가 바뀜에 따라서 객체의 행동을 바꿀수 있습니다. 마치 객체의 클래스가 바뀌는 것과 같은 결과를 얻을 수 있습니다.

구조

• context : 여러가지 내부 상태를 가질 수 있음.

• state : 구상 상태 클래스에 대한 공통 인터페이스를 정의함.

• concrete state : context로부터 전달된 요청을 처리함. 요청의 처리 방식을 자기 나름의 방식으로 구현함.

특징

적용 결과

• GumballMachine.java

package example.gumballstate;

public class GumballMachine {
 
	State soldOutState;
	State noQuarterState;
	State hasQuarterState;
	State soldState;
 
	State state;
	int count = 0;
 
	public GumballMachine(int numberGumballs) {
		soldOutState = new SoldOutState(this);
		noQuarterState = new NoQuarterState(this);
		hasQuarterState = new HasQuarterState(this);
		soldState = new SoldState(this);

		this.count = numberGumballs;
 		if (numberGumballs > 0) {
			state = noQuarterState;
		} else {
			state = soldOutState;
		}
	}
 
	public void insertQuarter() {
		state.insertQuarter();
	}
 
	public void ejectQuarter() {
		state.ejectQuarter();
	}
 
	public void turnCrank() {
		state.turnCrank();
		state.dispense();
	}
 
	void releaseBall() {
		System.out.println("A gumball comes rolling out the slot...");
		if (count > 0) {
			count = count - 1;
		}
	}
 
	int getCount() {
		return count;
	}
 
	void refill(int count) {
		this.count += count;
		System.out.println("The gumball machine was just refilled; its new count is: " + this.count);
		state.refill();
	}

	void setState(State state) {
		this.state = state;
	}
    public State getState() {
        return state;
    }

    public State getSoldOutState() {
        return soldOutState;
    }

    public State getNoQuarterState() {
        return noQuarterState;
    }

    public State getHasQuarterState() {
        return hasQuarterState;
    }

    public State getSoldState() {
        return soldState;
    }
 
	public String toString() {
		StringBuffer result = new StringBuffer();
		result.append("\nMighty Gumball, Inc.");
		result.append("\nJava-enabled Standing Gumball Model #2004");
		result.append("\nInventory: " + count + " gumball");
		if (count != 1) {
			result.append("s");
		}
		result.append("\n");
		result.append("Machine is " + state + "\n");
		return result.toString();
	}
}

• HasQuarterState.java

package example.gumballstate;

//import java.util.Random;

public class HasQuarterState implements State {
	GumballMachine gumballMachine;
 
	public HasQuarterState(GumballMachine gumballMachine) {
		this.gumballMachine = gumballMachine;
	}
  
	public void insertQuarter() {
		System.out.println("You can't insert another quarter");
	}
 
	public void ejectQuarter() {
		System.out.println("Quarter returned");
		gumballMachine.setState(gumballMachine.getNoQuarterState());
	}
 
	public void turnCrank() {
		System.out.println("You turned...");
		gumballMachine.setState(gumballMachine.getSoldState());
	}

    public void dispense() {
        System.out.println("No gumball dispensed");
    }
    
    public void refill() { }
 
	public String toString() {
		return "waiting for turn of crank";
	}
}

• State.java

package example.gumballstate;

public interface State {
 
	public void insertQuarter();
	public void ejectQuarter();
	public void turnCrank();
	public void dispense();
	
	public void refill();
}

추가 요구사항 반영 결과

• HasQuarterState.java

package example.gumballstatewinner;

import java.util.Random;

public class HasQuarterState implements State {
	Random randomWinner = new Random(System.currentTimeMillis());
	GumballMachine gumballMachine;
 
	public HasQuarterState(GumballMachine gumballMachine) {
		this.gumballMachine = gumballMachine;
	}
  
	public void insertQuarter() {
		System.out.println("You can't insert another quarter");
	}
 
	public void ejectQuarter() {
		System.out.println("Quarter returned");
		gumballMachine.setState(gumballMachine.getNoQuarterState());
	}
 
	public void turnCrank() {
		System.out.println("You turned...");
		int winner = randomWinner.nextInt(10);
		if ((winner == 0) && (gumballMachine.getCount() > 1)) {
			gumballMachine.setState(gumballMachine.getWinnerState());
		} else {
			gumballMachine.setState(gumballMachine.getSoldState());
		}
	}

    public void dispense() {
        System.out.println("No gumball dispensed");
    }
    
    public void refill() { }
 
	public String toString() {
		return "waiting for turn of crank";
	}
}

비교 분석

• strategy vs state.

항목	strategy	state
구조
정의	실행 중에 알고리즘을 선택할 수 있게 하는 행위 소프트웨어 디자인 패턴이다	객체의 내부 상태가 바뀜에 따라서 객체의 행동을 바꿀수 있습니다. 마치 객체의 클래스가 바뀌는 것과 같은 결과를 얻을 수 있습니다
case	상속을 대체하려는 목적	코드내의 조건문들을 대체하려는 목적
특징	client에서 전략(객체)클래스를 유연하게 바꾸기도 함.	객체 내부상태가 이미 정해진 규칙에 의해 자동으로 바뀌는 case가 많음.

활용

• java api 사용 예시.
  javax.faces.lifecycle.LifeCycle#execute() (controlled by FacesServlet, the behaviour is dependent on current phase (state) of JSF lifecycle)
  https://stackoverflow.com/questions/1673841/examples-of-gof-design-patterns-in-javas-core-libraries/2707195#2707195

• c# 게임 구현시 사용 예시.
  https://github.com/gianlucadelfino/Finite-State-Machine-Pattern

연습문제

• 다음과 같은 전등 상태 다이어그램을 보고 구현해봅시다~