在商城系统中使用设计模式----策略模式

public interface GoodsActivity {

    /**
     * 获取应该支付的金额
     * @param amount 商品的单价
     * @return
     */
    BigDecimal getPayPrice(BigDecimal amount);

}

/**
 * 商品折扣活动
 *
 * @author chen
 * @create 2019-04-01 14:44
 **/
public class DiscountActivity implements GoodsActivity {

    //折扣
    private double discount;

    public DiscountActivity(double discount){
        this.discount = discount;
    }

    @Override
    public BigDecimal getPayPrice(BigDecimal amount) {
        return new BigDecimal(discount).multiply(amount).divide(new BigDecimal(10));
    }
}

/**
 * 满减活动
 *
 * @author chen
 * @create 2019-04-01 14:48
 **/
public class FullReduceActivity implements GoodsActivity {

    //满多少
    private BigDecimal fullAmount;

    //减多少
    private BigDecimal reductionAmount;

    public FullReduceActivity(BigDecimal fullAmount,BigDecimal reductionAmount){
        this.fullAmount=fullAmount;
        this.reductionAmount=reductionAmount;
    }

    @Override
    public BigDecimal getPayPrice(BigDecimal amount) {
        return amount.compareTo(fullAmount)>=0?amount.subtract(reductionAmount):amount;
    }
}

/**
 * 积分抵扣
 *
 * @author chen
 * @create 2019-04-01 14:58
 **/
public class IntegralActivity implements GoodsActivity {

    //抵扣的积分  10积分=1元
    private int integral;

    public IntegralActivity(int integral){
        this.integral = integral;
    }

    @Override
    public BigDecimal getPayPrice(BigDecimal amount) {
        return amount.subtract(new BigDecimal(integral/10));
    }
}

public class GoodsActivityContext {

    private GoodsActivity goodsActivity;

    public GoodsActivityContext(GoodsActivity goodsActivity){
        this.goodsActivity=goodsActivity;
    }

    /**
     * 获取商品价格
     * @param amount
     * @return
     */
    public BigDecimal getPrice(BigDecimal amount){
        return goodsActivity.getPayPrice(amount);
    }
}

public class StrategyMain {

    /**
     *
     * 在商城系统中，经常有不同的活动，每种活动商品的价格计算可能都不一样
     * 比如：会员折扣，满减，积分抵扣.....
     *
     * @param args
     */
    public static void main(String[] args) {

        //商品价格
        BigDecimal amount = new BigDecimal(500);

        //满300-100
        GoodsActivity fullReduceActivity = new FullReduceActivity(new BigDecimal(300),new BigDecimal(100) );
        GoodsActivityContext goodsActivityContext = new GoodsActivityContext(fullReduceActivity);
        System.out.println("满减活动："+goodsActivityContext.getPrice(amount));

        //折扣活动
        GoodsActivity discountActivity = new DiscountActivity(9);
        goodsActivityContext = new GoodsActivityContext(discountActivity);
        System.out.println("折扣活动："+goodsActivityContext.getPrice(amount));

        //积分抵扣活动
        GoodsActivity integralActivity = new IntegralActivity(100);
        goodsActivityContext = new GoodsActivityContext(integralActivity);
        System.out.println("积分抵扣活动："+goodsActivityContext.getPrice(amount));

    }