策略模式在商场促销中的应用

在商场促销场景下，使用策略模式可以有效地实现计算最终支付金额的功能。本文将详细介绍相关实现。

收费基类

package com.zawl.designpattern.strategy;
public interface CashSuper {
    BigDecimal acceptCash(BigDecimal money);
}

该接口定义了一个通用收费处理方法，用于计算最终支付金额。

正常收费类

package com.zawl.designpattern.strategy;
public class CashNormal implements CashSuper {
    @Override
    public BigDecimal acceptCash(BigDecimal money) {
        return money;
    }
}

实现了接口中的acceptCash方法，直接返回输入金额，不做任何调整。

折扣收费类

package com.zawl.designpattern.strategy;
public class CashDiscount implements CashSuper {
    private BigDecimal discountRate = new BigDecimal(1);
    public CashDiscount(BigDecimal discountRate) {
        this.discountRate = discountRate;
    }
    @Override
    public BigDecimal acceptCash(BigDecimal money) {
        return money.multiply(discountRate).setScale(2, BigDecimal.ROUND_HALF_UP);
    }
}

支持打折收费，根据输入的折扣率计算最终金额。

返现收费类

package com.zawl.designpattern.strategy;
public class CashReturn implements CashSuper {
    private BigDecimal moneyCondition = BigDecimal.ZERO;
    private BigDecimal moneyReturn = BigDecimal.ZERO;
    public CashReturn(double moneyCondition, double moneyReturn) {
        this.moneyCondition = new BigDecimal(moneyCondition);
        this.moneyReturn = new BigDecimal(moneyReturn);
    }
    @Override
    public BigDecimal acceptCash(BigDecimal money) {
        if (money.compareTo(moneyCondition) >= 0) {
            money = money.subtract(moneyReturn);
        }
        return money;
    }
}

支持返现收费，根据消费金额和满足返现条件计算最终金额。

收费上下文对象

package com.zawl.designpattern.strategy;
public class CashContext {
    private CashSuper cashSuper;
    public CashContext(String type) {
        switch (type) {
            case CashConstants.NORMAL:
                cashSuper = new CashNormal();
                break;
            case CashConstants.DISCOUNT:
                cashSuper = new CashDiscount(new BigDecimal(0.8));
                break;
            case CashConstants.RETURN:
                cashSuper = new CashReturn(300, 100);
                break;
        }
    }
    public BigDecimal getResult(double money) {
        return cashSuper.acceptCash(new BigDecimal(money));
    }
    enum CashEnum {
        NORMAL("正常收费", "1"),
        DISCOUNT("打折收费", "2"),
        RETURN("返现收费", "3");
        CashEnum(String key, String value) {
            this.key = key;
            this.value = value;
        }
        private String key;
        private String value;
        public String getKey() {
            return key;
        }
        public String getValue() {
            return value;
        }
    }
}

该类用于根据不同的收费策略选择合适的处理逻辑，提供计算最终支付金额的功能。

收费类型常量类

package com.zawl.designpattern.strategy;
public class CashConstants {
    public static final String NORMAL = "NORMAL";
    public static final String DISCOUNT = "DISCOUNT";
    public static final String RETURN = "RETURN";
}

定义了常用的收费类型标识符，供上下文对象使用。

客户端调用

package com.zawl.designpattern.strategy;
public class Client {
    public static void main(String[] args) {
        CashContext context = new CashContext(CashConstants.RETURN);
        BigDecimal result = context.getResult(300);
        System.out.println("最终收费：" + result.toString());
        context = new CashContext(CashConstants.NORMAL);
        result = context.getResult(300);
        System.out.println("最终收费：" + result.toString());
        context = new CashContext(CashConstants.DISCOUNT);
        result = context.getResult(300);
        System.out.println("最终收费：" + result.toString());
    }
}

客户端代码用于创建不同的收费策略上下文，调用计算最终支付金额的方法。