Java设计模式之策略模式、模板模式

对于业务代码中有多个if时，可以采用策略模式，将多个if里的算法封装为多个处理器(handler)，再通过工厂方法去获取相应的处理器。

如果if里的算法有共同特征，提取为抽象方法，handler去继承实现。

/**
 * 打折模板
 * @author XinHai.Ma
 *
 */
public class Discount {

    /**
     * 打折方法
     * @return
     */
    public String discount() {
        return null;
    }

}

/**
 * 初级会员打折策略
 * @author XinHai.Ma
 *
 */
public class PrimaryMember extends Discount {

    @Override
    public String discount() {
        return "0.8";
    }
}

/**
 * 中级会员打折策略
 * @author XinHai.Ma
 *
 */
public class IntermediateMember extends Discount {

    @Override
    public String discount() {
        return "0.7";
    }
}

/**
 * 高级会员打折策略
 * @author XinHai.Ma
 *
 */
public class AdvancedMember extends Discount {

    @Override
    public String discount() {
        return "0.6";
    }

}

import java.math.BigDecimal;

/**
 * 类描述: 价格类
 * @Author: XinHai.Ma
 * @Date: 2020/8/23 14:51
 */
public class Price {

    /**
     * 打折策略对象
     */
    private Discount discount;

    public Price(Discount discount) {
        this.discount = discount;
    }

    /**
     * 计算价格
     * @param amount
     * @param discount
     * @return
     */
    public double calculation(String amount, String discount) {
        //原价
        BigDecimal originalPrice = new BigDecimal(amount);
        //会员折扣
        BigDecimal memberDiscount = new BigDecimal(discount);
        return originalPrice.multiply(memberDiscount).setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();
    }

}

/**
 * 类描述: 折扣工厂
 * @Author: XinHai.Ma
 * @Date: 2020/8/23 15:05
 */
public class DiscountFactory {

    private DiscountFactory() {}

    /**
     * 功能描述: 根据用户等级获取折扣
     * @Param: [member]
     * @Return: www.maxinhai.com.Discount
     * @Author: 15735400536
     * @Date: 2020/8/23 15:04
     */
    public static Discount getDiscount(String member) {
        Discount discount = null;
        switch (member) {
            case "普通会员":
                discount = new PrimaryMember();
            case "中级会员":
                discount = new IntermediateMember();
            case "高级会员":
                discount = new AdvancedMember();
        }
        return discount;
    }

}

public class PriceDemo {

    public static void main(String[] args) {

        Discount discount = DiscountFactory.getDiscount("中级会员");
        Price price = new Price(discount);
        String amount = "216.8";
        double calculation = price.calculation(amount, discount.discount());
        System.out.println("优惠折扣: " + discount.discount());
        System.out.println("打折后价格: " + calculation);
    }

}