设计模式之策略模式

策略模式介绍

当我们的代码中出现好多if…else…或者case的时候,代码看起来会很多很臃肿,策略模式就能很好的解决这个问题.
使用场景:
1.针对同一类型问题的多种处理方式，仅仅是具体行为有差别时；
2.需要安全地封装多种同一类型的操作时；
3.出现同一抽象类有多个子类，而又需要使用 if-else 或者 switch-case 来选择具体子类时。

由图可看出此模式分为三个角色:
环境角色(Context): 持有抽象策略角色的引用.
抽象策略角色(Strategy): 具体策略角色的接口.
具体策略角色(ConcreteStrategy): 包装了算法和行为.

策略模式的实现

环境角色(Context)

public class Context {
    
    Strategy strategy;
    
    public Context(Strategy strategy) {
        this.strategy = strategy;
    }
    
    //上下文接口
    public void contextInterface() {
        strategy.algorithmInterface();
    }

}

抽象策略角色(Strategy)

public abstract class Strategy {
     
     //算法方法
     public abstract void algorithmInterface();
 
}

具体策略角色(ConcreteStrategy)

public class ConcreteStrategyA extends Strategy {

    @Override
    public void algorithmInterface() {
        System.out.println("算法A实现");
    }

}

public class ConcreteStrategyB extends Strategy {

    @Override
    public void algorithmInterface() {
        System.out.println("算法B实现");
    }

}

public class ConcreteStrategyC extends Strategy {

    @Override
    public void algorithmInterface() {
        System.out.println("算法C实现");
    }

}

测试类

public class Client {
    public static void main(String[] args) {
        Context context;
        
        context = new Context(new ConcreteStrategyA());
        context.contextInterface();
        
        context = new Context(new ConcreteStrategyB());
        context.contextInterface();
        
        context = new Context(new ConcreteStrategyC());
        context.contextInterface();
    }
}

算法A实现
算法B实现
算法C实现

策略模式的实现

context环境角色

public class CashContext {
    
    private CashSuper cashSuper;
    
    public CashContext(CashSuper cashSuper) {
        this.cashSuper = cashSuper;
    }
    
    public double getResult(double money) {
        return cashSuper.acceptCash(money);
    }

}

现金收费抽象类

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

具体策略角色
正常收费子类

public class CashNormal extends CashSuper {

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

}

打折收费子类

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;
    }

}

返利收费子类

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;
    }

}

client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();
    }

}

请输入打折方式(1/2/3):1
请输入单价:100
请输入数量:5
单价：100，数量：5，类型：正常计费，合计：500.0

请输入打折方式(1/2/3):1
请输入单价:100
请输入数量:5
单价：100，数量：5，类型：满300反100，合计：400.0

请输入打折方式(1/2/3):1
请输入单价:100
请输入数量:5
单价：100，数量：5，类型：打八折，合计：400.0