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设计方式之状态模式(state model)

2013-10-16 
设计模式之状态模式(state model)状态模式适用于实际类型之间需要不断切换,如商品、结账、实际支付这样一条

设计模式之状态模式(state model)

状态模式适用于实际类型之间需要不断切换,如商品、结账、实际支付这样一条龙流水线,这期间存在着一个session用户的状态切换。通过一个实现了接口的控制器类来控制各实际类状态的切换,具体控制实现的方法是在另一个上下文类中实现。各实现类都实现了单例模式。

package StateMethod;


public interface IShopState {
    public void shop();
    public void generateBill();
    public void pay();
    //protected void changeState(ShopContext c, IShopState);
}


package StateMethod;


public class ShopState implements IShopState { 
    public ShopState() {
    }
    public void shop() { }
    public void generateBill() { }
    public void pay() { }
    protected void changeState(ShopContext c, ShopState s) {
        c.changeState(s);
    }
}


package StateMethod;


public class Shop extends ShopState {
    public static boolean instanceFlag = false; //true if have 1 instance
    private Shop() {
    }
    public static Shop getInstance() {
        if(! instanceFlag) {
            instanceFlag = true;
            return new Shop();
        }
        return null;
    }
    public void shop() {
        System.out.println("The state is shopping now !");
    }
}


package StateMethod;


public class GenerateBill extends ShopState {
    public static boolean instanceFlag = false; //true if have 1 instance
    private GenerateBill() {
    }
    public static GenerateBill getInstance() {
        if(! instanceFlag) {
            instanceFlag = true;
            return new GenerateBill();
        }
        return null;
    }
    public void generateBill() {
        System.out.println("The state is generating bill now !");
    }
}


package StateMethod;


public class Pay extends ShopState {
    public static boolean instanceFlag = false; //true if have 1 instance
    private Pay() {
    }
    public static Pay getInstance() {
        if(! instanceFlag) {
            instanceFlag = true;
            return new Pay();
        }
        return null;
    }
    public void pay() {
        System.out.println("The state is pay now !");
    }
}


package StateMethod;


public class ShopContext  {
    private ShopState currentState;
    public ShopContext() {
    }
    public void changeState(ShopState s) {
        currentState = s;
    }
    public void shop() {
        currentState.shop();
    }
    public void generateBill() {
        currentState.generateBill();
    }
    public void pay() {
        currentState.pay();
    }
}


package StateMethod;


public class Test {
public static void main(String[] args) {
        ShopContext myContext = new ShopContext();
        ShopState myShop = Shop.getInstance();
        ShopState myGenBill = GenerateBill.getInstance();
        ShopState myPay = Pay.getInstance();
        
        myContext.changeState(myShop);
        myContext.shop();


        myContext.changeState(myGenBill);
        myContext.generateBill();
        
        myContext.changeState(myPay);
        myContext.pay();


        myShop.changeState(myContext, myPay);
        myContext.pay();
    }
}


输出:

The state is shopping now !
The state is generating bill now !
The state is pay now !
The state is pay now !

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