策略模式 Strategy

策略模式是一种行为型模式，它将对象和行为分开，将行为定义为 一个行为接口 和 具体行为的实现。策略模式最大的特点是行为的变化，行为之间可以相互替换。每个 if 判断都可以理解为就是一个策略。

封装计算价格策略模式接口类

package com.learn.strategy;

/**
 * 场景：拼车、快车、商务车
 * 三种计费方式，就是行为，可以根据不同行为的计算方式计算不同的费用
 * 抽象成一个价格计算接口类
 * 定义一个 PriceContext 环境类，启承上启下的封装作用, 负责和策略接口类交互
 * 具体的打车场景实现 PriceStrategy 接口类
 */
public interface PriceStrategy {Double calculatePrice(Double price);

}

计算价格上下文环境类

package com.learn.strategy;

/**
 * PriceContext 环境类
 */
public class PriceContext {

    private PriceStrategy priceStrategy;

    public PriceContext(PriceStrategy priceStrategy) {this.priceStrategy = priceStrategy;}

    public Double calculatePrice(Double price) {return priceStrategy.calculatePrice(price);
    }
}

场景 1: 拼车

package com.learn.strategy;

/**
 * 拼车场景
 */
public class CarPool implements PriceStrategy {

    @Override
    public Double calculatePrice(Double price) {return price * 0.5;}

    public static void main(String[] args) {CarPool carPool = new CarPool();
        PriceContext carContext = new PriceContext(carPool);

        System.out.println(carContext.calculatePrice(10D));
    }
}

场景二: 快车

package com.learn.strategy;

/**
 * 快车场景
 */
public class ExpressTrain implements PriceStrategy{

    @Override
    public Double calculatePrice(Double price) {return price * 1.5;}

    public static void main(String[] args) {ExpressTrain expressTrain = new ExpressTrain();
        PriceContext expressContext = new PriceContext(expressTrain);

        System.out.println(expressContext.calculatePrice(10D));
    }
}

场景三：商务车

package com.learn.strategy;

/**
 * 商务车
 */
public class BusinessCar implements PriceStrategy{
    @Override
    public Double calculatePrice(Double price) {return price * 3;}

    public static void main(String[] args) {BusinessCar businessCar = new BusinessCar();
        PriceContext businessContext = new PriceContext(businessCar);

        System.out.println(businessContext.calculatePrice(10D));
    }
}