策略模式

策略模式(Strategy),是一种定义一系列算法的方法，从概念上来看，所有这些算法完成的都是相同的工作，只是实现不同。它可以以相同的方式调用所有的算法，减少了各种算法类与使用算法类之间耦合。

策略模式就是用来封装算法的，但在实践中，我们发现可以用它来封装几乎任何类型的规则，只要在分析过程中听到需要在不同时间应用不同的业务规则，就可以考虑使用策略模式处理这种变化的可能性。

CashCollect.java类

package strategy;

import java.math.BigDecimal;

public abstract class CashCollect {
    public abstract BigDecimal cashCollect(BigDecimal total);
    
}

DisCountCashCollect.java类

package strategy;

import java.math.BigDecimal;

public class DisCountCashCollect extends CashCollect {
    private BigDecimal discount;
    
    public DisCountCashCollect(BigDecimal discount) {
        super();
        this.discount = discount;
    }

    @Override
    public BigDecimal cashCollect(BigDecimal total) {
        System.out.println(total);
        System.out.println(discount);
        return total.multiply(discount);
    }

}

NormalCashCollect.java类

package strategy;

import java.math.BigDecimal;

public class NormalCashCollect extends CashCollect {

    @Override
    public BigDecimal cashCollect(BigDecimal total) {
        return total;
    }

}

RebateCashCollect.java类

package strategy;

import java.math.BigDecimal;

public class RebateCashCollect extends CashCollect {
    private BigDecimal fullMoney;
    private BigDecimal returnMoney;
    
    public RebateCashCollect(BigDecimal fullMoney, BigDecimal returnMoney) {
        super();
        this.fullMoney = fullMoney;
        this.returnMoney = returnMoney;
    }

    @Override
    public BigDecimal cashCollect(BigDecimal total) {
        if(fullMoney.compareTo(total)>=0){
            total = total.subtract(returnMoney);
        }
        return total;
    }

}

CashContext.java类

package strategy;

import java.math.BigDecimal;

public class CashContext {
    CashCollect cc ;

    /*public CashContext(CashCollect cc) {
        super();
        this.cc = cc;
    }*/
    public CashContext(String type){
        switch(type){
            case "原价":
                cc = new NormalCashCollect();
                break;
            case "打8折":
                cc = new DisCountCashCollect(new BigDecimal("0.8"));
                break;
            case "满300返100":
                cc = new RebateCashCollect(new BigDecimal("300"), new BigDecimal("100"));
                break;
        }
    }
    public BigDecimal cashCollect(BigDecimal total ){
        return cc.cashCollect(total);
    }
    
    
}

BusinessStrategy.java类

package strategy;

import java.math.BigDecimal;
/**
 * 策略模式
 * @author 煞笔
 *
 */

public class BusinessStrategy {

    public static void main(String[] args) {
        //BigDecimal total = new BigDecimal("1000");
        CashContext cct = new CashContext("打8折");
        //cct.total = total;
        BigDecimal total = cct.cashCollect(new BigDecimal("1000"));
        System.out.println(total);
    }

}