策略模式 电商 java示例

策略模式（Strategy Pattern）是一种行为型设计模式，它允许在运行时选择算法的行为。在该模式中，算法被封装在独立的策略类中，客户端代码可以通过组合和委托来实现不同的行为。

在电商系统中，可以使用策略模式来实现不同的促销策略，如满减、折扣、赠品等。下面是一个简单的Java示例：

首先，我们定义一个促销策略接口：

public interface PromotionStrategy {
    double applyDiscount(double price);
}

然后，我们实现不同的促销策略：

public class DiscountPromotionStrategy implements PromotionStrategy {
    private double discount;

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

    @Override
    public double applyDiscount(double price) {
        return price * discount;
    }
}

public class FullReductionPromotionStrategy implements PromotionStrategy {
    private double full;
    private double reduction;

    public FullReductionPromotionStrategy(double full, double reduction) {
        this.full = full;
        this.reduction = reduction;
    }

    @Override
    public double applyDiscount(double price) {
        if (price >= full) {
            return price - reduction;
        }
        return price;
    }
}

public class GiftPromotionStrategy implements PromotionStrategy {
    private String gift;

    public GiftPromotionStrategy(String gift) {
        this.gift = gift;
    }

    @Override
    public double applyDiscount(double price) {
        System.out.println("送您一份礼物：" + gift);
        return price;
    }
}

最后，我们在购物车类中使用策略模式来选择不同的促销策略：

public class ShoppingCart {
    private List<Double> items = new ArrayList<>();
    private PromotionStrategy promotionStrategy;

    public void addItem(double price) {
        items.add(price);
    }

    public void setPromotionStrategy(PromotionStrategy promotionStrategy) {
        this.promotionStrategy = promotionStrategy;
    }

    public double calculateTotal() {
        double total = items.stream().mapToDouble(Double::doubleValue).sum();
        if (promotionStrategy != null) {
            total = promotionStrategy.applyDiscount(total);
        }
        return total;
    }
}

使用示例：

ShoppingCart cart = new ShoppingCart();
cart.addItem(100);
cart.addItem(200);
cart.addItem(300);

// 使用折扣策略
cart.setPromotionStrategy(new DiscountPromotionStrategy(0.8));
double total1 = cart.calculateTotal();
System.out.println("折扣后总价：" + total1); // 折扣后总价：480.0

// 使用满减策略
cart.setPromotionStrategy(new FullReductionPromotionStrategy(500, 100));
double total2 = cart.calculateTotal();
System.out.println("满减后总价：" + total2); // 满减后总价：500.0

// 使用赠品策略
cart.setPromotionStrategy(new GiftPromotionStrategy("小熊玩具"));
double total3 = cart.calculateTotal();
System.out.println("赠品后总价：" + total3); // 赠品后总价：600.0

这样，我们就可以根据需求灵活地选择不同的促销策略，而不需要修改购物车类的代码。