策略模式（Strategy Pattern）

策略模式（Strategy Pattern） 是一种行为型设计模式，它允许你在运行时选择算法或行为的具体实现。

✅ 核心思想：定义一系列算法，并将每种算法封装起来，使它们可以互换。

这使得算法的变化独立于使用它的客户端代码 ------ 符合"开闭原则"（对扩展开放，对修改关闭）。

java 复制代码

/**
 * 支付策略接口
 */
public interface PaymentStrategy {
    /**
     * 执行支付
     * @param amount 支付金额
     * @return 支付结果
     */
    boolean pay(double amount);
}

java 复制代码

/**
 * 支付宝支付策略实现
 */
public class AlipayStrategy implements PaymentStrategy {
    
    @Override
    public boolean pay(double amount) {
        System.out.println("使用支付宝支付: ¥" + String.format("%.2f", amount));
        // 模拟支付流程
        System.out.println("正在跳转至支付宝...");
        System.out.println("请扫码完成支付");
        System.out.println("支付成功!");
        return true;
    }
}

java 复制代码

/**
 * 微信支付策略实现
 */
public class WechatPayStrategy implements PaymentStrategy {
    
    @Override
    public boolean pay(double amount) {
        System.out.println("使用微信支付: ¥" + String.format("%.2f", amount));
        // 模拟支付流程
        System.out.println("正在跳转至微信...");
        System.out.println("请扫码完成支付");
        System.out.println("支付成功!");
        return true;
    }
}

java 复制代码

/**
 * 信用卡支付策略实现
 */
public class CreditCardStrategy implements PaymentStrategy {
    
    private String cardNumber;
    private String cvv;
    private String dateOfExpiry;

    public CreditCardStrategy(String cardNumber, String cvv, String dateOfExpiry) {
        this.cardNumber = cardNumber;
        this.cvv = cvv;
        this.dateOfExpiry = dateOfExpiry;
    }

    @Override
    public boolean pay(double amount) {
        System.out.println("使用信用卡支付: ¥" + String.format("%.2f", amount));
        System.out.println("卡号: " + maskCardNumber(cardNumber));
        System.out.println("验证信用卡信息...");
        System.out.println("扣款成功!");
        return true;
    }

    private String maskCardNumber(String cardNumber) {
        if (cardNumber == null || cardNumber.length() < 4) {
            return "****";
        }
        return "**** **** **** " + cardNumber.substring(cardNumber.length() - 4);
    }
}

java 复制代码

/**
 * 支付上下文类，用于管理支付策略
 */
public class PaymentContext {
    
    private PaymentStrategy strategy;

    /**
     * 构造函数
     * @param strategy 支付策略
     */
    public PaymentContext(PaymentStrategy strategy) {
        this.strategy = strategy;
    }

    /**
     * 执行支付
     * @param amount 支付金额
     * @return 支付结果
     */
    public boolean executePayment(double amount) {
        return strategy.pay(amount);
    }

    /**
     * 更换支付策略
     * @param strategy 新的支付策略
     */
    public void setPaymentStrategy(PaymentStrategy strategy) {
        this.strategy = strategy;
    }
}

java 复制代码

/**
 * 订单类
 */
public class Order {
    private String orderId;
    private double amount;

    public Order(String orderId, double amount) {
        this.orderId = orderId;
        this.amount = amount;
    }

    public String getOrderId() {
        return orderId;
    }

    public double getAmount() {
        return amount;
    }

    @Override
    public String toString() {
        return "Order{" +
                "orderId='" + orderId + '\'' +
                ", amount=¥" + String.format("%.2f", amount) +
                '}';
    }
}

java 复制代码

/**
 * 策略模式演示应用程序
 * 模拟电商平台的订单支付场景
 */
public class PaymentApplication {

    public static void main(String[] args) {
        // 场景一：用户选择支付宝支付
        System.out.println("=== 订单支付场景演示 ===");
        Order order1 = new Order("ORD001", 299.99);
        PaymentStrategy alipayStrategy = new AlipayStrategy();
        PaymentContext context = new PaymentContext(alipayStrategy);
        
        System.out.println(order1);
        context.executePayment(order1.getAmount());
        System.out.println();

        // 场景二：用户更换为微信支付
        System.out.println("用户改变主意，选择微信支付...");
        PaymentStrategy wechatPayStrategy = new WechatPayStrategy();
        context.setPaymentStrategy(wechatPayStrategy);
        context.executePayment(order1.getAmount());
        System.out.println();

        // 场景三：大额订单使用信用卡支付
        Order order2 = new Order("ORD002", 1999.00);
        System.out.println("大额订单:");
        System.out.println(order2);
        PaymentStrategy creditCardStrategy = new CreditCardStrategy("1234567890123456", "123", "12/28");
        context.setPaymentStrategy(creditCardStrategy);
        context.executePayment(order2.getAmount());
    }
}