大話設計模式二：策略模式（商場促銷）

  策略模式：它定義了算法家族，分別封裝起來，讓它們之間可以相互替換，此模式讓算法的變化，不會影響到使用的算法客戶。 </span>

     應用案例：商場促銷的多樣性（折扣，滿減，積分）

    package Strategy;


abstract class CashSuper {  
    public abstract double acceptCash(double money);  
}  

class CashNormal extends CashSuper {  

    @Override  
    public double acceptCash(double money) {  
        return money;  
    }  
}  

class CashRebate extends CashSuper {  
    private double moneyRebate = 1d;  

    public CashRebate(String moneyRebate) {  
        this.moneyRebate = Double.parseDouble(moneyRebate);  
    }  

    @Override  
    public double acceptCash(double money) {  
        return money * moneyRebate;  
    }  
}  

class CashReturn extends CashSuper {  
    private double moneyCondition = 0.0d;  
    private double moneyReturn = 0.0d;  

    public CashReturn(String moneyCondition, String moneyReturn) {  
        this.moneyCondition = Double.parseDouble(moneyCondition);  
        this.moneyReturn = Double.parseDouble(moneyReturn);  
    }  

    @Override  
    public double acceptCash(double money) {  
        double result = money;  
        if (money >= moneyCondition) {  
            result = money - Math.floor(money / this.moneyCondition)  
                    * this.moneyReturn;  
        }  
        return result;  
    }  
}  

public class CashContext {  
    private CashSuper cs;  

    public CashContext(String type) {  
        switch(type) {  
        case "正常收費":  
            cs = new CashNormal();  
            break;  
        case "滿300返100":  
            cs = new CashReturn("300","100");  
            break;  
        case "打8折":  
            cs =new CashRebate("0.8");  
            break;  
        }  
    }  

    public double GetResult(double money) {  
        return cs.acceptCash(money);  
    }  

    public static void main(String[] args) {  
        // TODO Auto-generated method stub  
        CashContext cc = null;  
        double total = 0.0d,totalprice = 1000d;  
        cc = new CashContext("正常收費");  
        total = cc.GetResult(totalprice);  
        System.out.println(total);  

        total = 0.0d;  
        totalprice = 1000d;  
        cc = new CashContext("滿300返100");  
        total = cc.GetResult(totalprice);  
        System.out.println(total);  

        total = 0.0d;  
        totalprice = 1000d;  
        cc = new CashContext("打8折");  
        total = cc.GetResult(totalprice);  
        System.out.println(total);  
    }  
}  </pre></span></span> <p></p>

     策略模式就是用來封裝算法的，在實踐中，我們發現可以用來封裝幾乎任何類型的規則，只要在分析中聽到需要在不同時間應用不同的業務規則，就可以考慮使用策略模式處理這種變化的可能性。