按变量选择接口实现

// 定义接口
interface PaymentStrategy {
    void pay(double amount);
}

// 实现接口的具体策略类
class AlipayStrategy implements PaymentStrategy {
    @Override
    public void pay(double amount) {
        System.out.println("使用支付宝支付 " + amount + " 元");
    }
}

class WechatPayStrategy implements PaymentStrategy {
    @Override
    public void pay(double amount) {
        System.out.println("使用微信支付 " + amount + " 元");
    }
}

// 工厂类
class PaymentStrategyFactory {
    public static PaymentStrategy getPaymentStrategy(String paymentMethod) {
        if ("alipay".equalsIgnoreCase(paymentMethod)) {
            return new AlipayStrategy();
        } else if ("wechat".equalsIgnoreCase(paymentMethod)) {
            return new WechatPayStrategy();
        } else {
            throw new IllegalArgumentException("Unsupported payment method: " + paymentMethod);
        }
    }
}

// 客户端代码
public class Client {
    public static void main(String[] args) {
        String paymentMethod = "alipay"; // 可以根据实际情况动态获取
        PaymentStrategy paymentStrategy = PaymentStrategyFactory.getPaymentStrategy(paymentMethod);
        paymentStrategy.pay(100.0);
    }
}