public class Factory {
    public static Product createProduct(String type) {
        if (type == null) {
            return null;
        }
        if (type.equalsIgnoreCase("A")) {
            return new ConcreteProductA();
        } else if (type.equalsIgnoreCase("B")) {
            return new ConcreteProductB();
        }
        return null;
    }
    
    // 添加测试方法
    public static void main(String[] args) {
        // 创建产品A
        Product productA = Factory.createProduct("A");
        productA.operation();
        
        // 创建产品B
        Product productB = Factory.createProduct("B");
        productB.operation();
    }
}