二十三种设计模式：解密职责链模式-购物优惠活动的设计艺术

// 抽象处理者
abstract class CouponHandler {
    protected CouponHandler nextHandler;
    public void setNextHandler(CouponHandler nextHandler) {
        this.nextHandler = nextHandler;
    }
    public abstract void handleCoupon(Order order);
}
// 具体处理者
class DiscountCouponHandler extends CouponHandler {
    public void handleCoupon(Order order) {
        if (order.getTotalAmount() >= 100) {
            double discount = order.getTotalAmount() * 0.1;
            order.setTotalAmount(order.getTotalAmount() - discount);
            System.out.println("Discount coupon applied. Total amount after discount: " + order.getTotalAmount());
        } else if (nextHandler != null) {
            nextHandler.handleCoupon(order);
        }
    }
}
class FreeGiftCouponHandler extends CouponHandler {
    public void handleCoupon(Order order) {
        if (order.getTotalAmount() >= 200) {
            order.addGift("Free T-shirt");
            System.out.println("Free gift coupon applied. Gift added: Free T-shirt");
        } else if (nextHandler != null) {
            nextHandler.handleCoupon(order);
        }
    }
}
class FullReductionCouponHandler extends CouponHandler {
    public void handleCoupon(Order order) {
        if (order.getTotalAmount() >= 300) {
            double reduction = 50;
            order.setTotalAmount(order.getTotalAmount() - reduction);
            System.out.println("Full reduction coupon applied. Total amount after reduction: " + order.getTotalAmount());
        } else if (nextHandler != null) {
            nextHandler.handleCoupon(order);
        }
    }
}

// 订单类
class Order {
    private double totalAmount;
    private List<String> gifts;
    public Order(double totalAmount) {
        this.totalAmount = totalAmount;
           }
    public double getTotalAmount() {
        return totalAmount;
    }
    public void setTotalAmount(double totalAmount) {
        this.totalAmount = totalAmount;
    }
    public void addGift(String gift) {
        if (gifts == null) {
            gifts = new ArrayList<>();
        }
        gifts.add(gift);
    }
    public void showGifts() {
        if (gifts != null && !gifts.isEmpty()) {
            System.out.println("Gifts:");
            for (String gift : gifts) {
                System.out.println("- " + gift);
            }
        }
    }
}
// 职责链构建器
class CouponChainBuilder {
    public CouponHandler build() {
        CouponHandler discountHandler = new DiscountCouponHandler();
        CouponHandler freeGiftHandler = new FreeGiftCouponHandler();
        CouponHandler fullReductionHandler = new FullReductionCouponHandler();
        discountHandler.setNextHandler(freeGiftHandler);
        freeGiftHandler.setNextHandler(fullReductionHandler);
        return discountHandler;
    }
}

public class Client {
    public static void main(String[] args) {
        Order order = new Order(250);
        CouponChainBuilder builder = new CouponChainBuilder();
        CouponHandler handler = builder.build();
        handler.handleCoupon(order);
        order.showGifts();
    }
}

Discount coupon applied. Total amount after discount: 225.0
Free gift coupon applied. Gift added: Free T-shirt
Gifts:
- Free T-shirt