23种设计模式-策略模式

策略模式：定义一系列的算法,把每一个算法封装起来, 并且使它们可相互替换。本模式使得算法可独立于使用它的客户而变化。也称为政策模式(Policy)。

目的：为了让算法和对象独立出来，代替if判断方式
举例：商场商品促销方法

//声明一个CashSuper对象，通过构造方法，传入具体的收费策略，
//getResult()方法的功能为根据收费策略的不同获得计算结果。
public class CashContext {
    
    

    private CashSuper cashSuper;

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

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

//策略类，为抽象类，抽象出收费的方法供子类实现。
public abstract class CashSuper {
    
    
     public abstract double acceptCash(double money); 
}

//没有任何活动的情况，正常收费，返回原价。
public class CashNormal extends CashSuper {
    
    
    @Override
    public double acceptCash(double money) {
    
    
        return money;
    }
}

//打折活动，根据折扣返回打折后的价格。
public class CashRebate extends CashSuper {
    
    
    private double moneyRebate = 1;    //折扣

    public CashRebate(double moneyRebate) {
    
    
        this.moneyRebate = moneyRebate;
    }

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

//返利活动，输入返利条件和返利值，比如满300返100
public class CashReturn extends CashSuper {
    
    

    private double moneyConditation = 0.0;    //返利条件
    private double moneyReturn = 0.0d;    //返利值

    public CashReturn(double moneyConditation, double moneyReturn) {
    
    
        this.moneyConditation = moneyConditation;
        this.moneyReturn = moneyReturn;
    }

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

//客户端
public class Client {
    
    
    public static void main(String[] args) {
    
    
        CashContext cashContext = null;
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入打折方式（1/2/3）：");
        int in = scanner.nextInt();
        String type = "";
        switch (in) {
    
    
            case 1:
                cashContext = new CashContext(new CashNormal());
                type += "正常收费";
                break;

            case 2:
                cashContext = new CashContext(new CashReturn(300, 100));
                type += "满300返100";
                break;

            case 3:
                cashContext = new CashContext(new CashRebate(0.8));
                type += "打8折";
                break;

            default:
                System.out.println("请输入1/2/3");
                break;
        }

        double totalPrices = 0;

        System.out.print("请输入单价：");
        double price = scanner.nextDouble();
        System.out.print("请输入数量：");
        double num = scanner.nextDouble();
        totalPrices = cashContext.getResult(price * num);

        System.out.println("单价：" + price + "，数量：" + num + "，类型：" + type + "，合计：" + totalPrices);

        scanner.close();
    }
}