策略模式（strategy）：它定义了算法家族，分别封装起来，让他们之间可以相互替换，此模式让算法的变化，不会影响到使用算法的客户。

主方法

/**
 * Created by king on 2017/7/6.
 */
public class main {
    public static void main(String[] args) {
        double total = 1000.0;
        int type = 2;
        CashContext cc = null;
        switch (type) {
            case 1 : //正常收费
                cc = new CashContext(new CashNormal());
                break;
            case 2 : //满300返100
                cc = new CashContext(new CashReturn(300,100));
                break;
            case 3: //打8折
                cc = new CashContext(new CashRebate(0.8));
                break;
        }
        System.out.println(cc.getResult(total));
    }
}

父类

public class CashContext {
    private  CashSuper cs;
    public CashContext (CashSuper cashSuper) {
        this.cs = cashSuper;
    }

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

子类

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

孙子类
正常收费

public class CashNormal extends CashSuper {
    @Override
    public double acceptCash(double money) {
        return money;
    }
}

满减

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

    public CashReturn(double moneyCondition, double moenyReturn) {
        this.moneyCondition = moneyCondition;
        this.moenyReturn = moenyReturn;
    }

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

折扣

public class CashRebate extends CashSuper {
    private double moneyRebate = 1d;
    public CashRebate(double moneyRebate) {
        this.moneyRebate = moneyRebate;
    }
    @Override
    public double acceptCash(double money) {
        return money * moneyRebate;
    }
}