設計模式10——狀態模式

Head Frist 設計模式11-狀態模式模式

如果餓了就喫，困了就睡，渴了就喝，人生就太無趣了
代碼地址：https://github.com/keer123456789/MY_STUDY_LIFE/tree/master/src/main/java/study/Module/Module_State

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1.定義

1.1概念

狀態模式允許對象在內部狀態改變時改變它的行爲，對象看起來好像修改了它的類。

1.2類圖

• 將所有的狀態抽象出一個共同接口state,讓不同的狀態都實現這個接口，這樣就可以實現不同狀態的轉換
• Context類擁有一些狀態，一旦有人調用request()方法，就委託到狀態state來實現。
• ConcreteState類處理來自Context的請求。

2.例子（糖果機）

給一個投幣糖果機進行程序設計。每次投25美分，就可以獲得一個口香糖。

2.1 狀態圖

現在需要給一個糖果機的程序進行設計，如圖2：狀態圖
一共是4個狀態：

• 沒有25分錢
• 有25分錢
• 糖果售罄
• 售出糖果

有5個動作：每一個動作都是糖果機的接口，調用每一個動作，都會造成狀態的轉換

• 投入25美分
• 轉動曲柄
• 退回25美分
• 發放糖果
• 填入糖果

2.2 類圖

如圖3：

• 根據剛纔得分析，將能改變狀態的5個動作進行抽象，形成State接口,接口方法分別是：insertQuarter()投幣，ejectQuart()退幣, turnCrank()轉動曲柄，dispense()分配糖果，refill()添加糖果
• 一共有四個狀態，都實現State接口，每個狀態對不同的動作接口做出不同的反應。

2.3 分析流程

如圖4

1. 糖果機的狀態爲沒有25美分NoQuarter，此時有投幣動作insertQuarter()時，將動作委託到NoQuarter狀態，進行狀態轉換，切換到HasQuarter有25美分狀態
2. 糖果機接收到轉動曲柄動作turnCrank(),將動作委託到當前狀態，狀態進行轉換，切換到Sold售出糖果狀態
3. 糖果機接收到出售糖果動作dispense(),將動作委託到當前狀態，狀態進行轉換，切換到NoQuarter無25美分狀態

3.代碼

3.1 狀態接口和實現類

/**
 * @BelongsProject: MY_STUDY_LIFE
 * @BelongsPackage: study.Module.Module_State
 * @Author: keer
 * @CreateTime: 2020-03-09 14:29
 * @Description: 狀態接口
 */
public interface State {
    /**
     * 投入25美分
     */
    void insertQuarter();

    /**
     * 退回25美分
     */
    void ejectQuarter();

    /**
     * 轉動曲柄
     */
    void turnCrank();

    /**
     * 分配糖果
     */
    void dispense();

    /**
     * 重新添加糖果
     */
    void refill();
}




/**
 * @BelongsProject: MY_STUDY_LIFE
 * @BelongsPackage: study.Module.Module_State
 * @Author: keer
 * @CreateTime: 2020-03-09 14:43
 * @Description: 沒有25美分狀態
 */
public class NoQuarterState implements State {
    GumballMachine gumballMachine;

    public NoQuarterState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("You inserted a quarter");
        gumballMachine.setState(gumballMachine.getHasQuarterState());
    }

    @Override
    public void ejectQuarter() {
        System.out.println("You haven't inserted a quarter");
    }

    @Override
    public void turnCrank() {
        System.out.println("You turned, but there's no quarter");
    }

    @Override
    public void dispense() {
        System.out.println("You need to pay first");
    }

    @Override
    public void refill() {

    }

    @Override
    public String toString() {
        return "waiting for quarter";
    }
}

/**
 * @BelongsProject: MY_STUDY_LIFE
 * @BelongsPackage: study.Module.Module_State
 * @Author: keer
 * @CreateTime: 2020-03-09 14:45
 * @Description: 有25美分狀態
 */
public class HasQuarterState implements State{
    GumballMachine gumballMachine;

    public HasQuarterState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("You can't insert another quarter");
    }

    @Override
    public void ejectQuarter() {
        System.out.println("Quarter returned");
        gumballMachine.setState(gumballMachine.getNoQuarterState());
    }

    @Override
    public void turnCrank() {
        System.out.println("You turned...");
        gumballMachine.setState(gumballMachine.getSoldState());
    }

    @Override
    public void dispense() {
        System.out.println("No gumball dispensed");
    }

    @Override
    public void refill() {

    }

    @Override
    public String toString() {
        return "waiting for turn of crank";
    }
}

/**
 * @BelongsProject: MY_STUDY_LIFE
 * @BelongsPackage: study.Module.Module_State
 * @Author: keer
 * @CreateTime: 2020-03-09 14:33
 * @Description: 售出糖果狀態
 */
public class SoldState implements State{
    GumballMachine gumballMachine;

    public SoldState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("Please wait, we're already giving you a gumball");
    }

    @Override
    public void ejectQuarter() {
        System.out.println("Sorry, you already turned the crank");
    }

    @Override
    public void turnCrank() {
        System.out.println("Turning twice doesn't get you another gumball!");
    }

    @Override
    public void dispense() {
        gumballMachine.releaseBall();
        if (gumballMachine.getCount() > 0) {
            gumballMachine.setState(gumballMachine.getNoQuarterState());
        } else {
            System.out.println("Oops, out of gumballs!");
            gumballMachine.setState(gumballMachine.getSoldOutState());
        }
    }

    @Override
    public void refill() {

    }

    @Override
    public String toString() {
        return "dispensing a gumball";
    }
}



/**
 * @BelongsProject: MY_STUDY_LIFE
 * @BelongsPackage: study.Module.Module_State
 * @Author: keer
 * @CreateTime: 2020-03-09 14:40
 * @Description: 售罄狀態
 */
public class SoldOutState implements State {
    GumballMachine gumballMachine;

    public SoldOutState(GumballMachine gumballMachine) {
        this.gumballMachine = gumballMachine;
    }

    @Override
    public void insertQuarter() {
        System.out.println("You can't insert a quarter, the machine is sold out");
    }

    @Override
    public void ejectQuarter() {
        System.out.println("You can't eject, you haven't inserted a quarter yet");
    }

    @Override
    public void turnCrank() {
        System.out.println("You turned, but there are no gumballs");
    }

    @Override
    public void dispense() {
        System.out.println("No gumball dispensed");
    }

    @Override
    public void refill() {
        gumballMachine.setState(gumballMachine.getNoQuarterState());
    }

    @Override
    public String toString() {
        return "sold out";
    }
}

3.2 糖果機代碼

**
 * @BelongsProject: MY_STUDY_LIFE
 * @BelongsPackage: study.Module.Module_State
 * @Author: keer
 * @CreateTime: 2020-03-09 14:35
 * @Description: 糖果機
 */
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; it's 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;
    }

    @Override
    public String toString() {
        StringBuffer result = new StringBuffer();
        result.append("\nMighty Gumball, Inc.");
        result.append("\nJava-enabled Standing Gumball Model #2020");
        result.append("\nInventory: " + count + " gumball");
        if (count != 1) {
            result.append("s");
        }
        result.append("\n");
        result.append("Machine is " + state + "\n");
        return result.toString();
    }
}

3.3 測試代碼

/**
 * @BelongsProject: MY_STUDY_LIFE
 * @BelongsPackage: study.Module.Module_State
 * @Author: keer
 * @CreateTime: 2020-03-09 14:53
 * @Description: 測試類
 */
public class GumballMachineTestDrive {
    public static void main(String[] args) {
        GumballMachine gumballMachine = new GumballMachine(2);

        System.out.println(gumballMachine);

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

        System.out.println(gumballMachine);

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

        gumballMachine.refill(5);
        gumballMachine.insertQuarter();
        gumballMachine.turnCrank();

        System.out.println(gumballMachine);
    }
}