11.4 适时地使用接口（interface）取代委托

Java 完全使用接口取代了委托功能。

以前面的模板方法举列，通过接口也能实现方法的可替换。

    class Program
    {
        static void Main(string[] args)
        {
            IProductFactory pizzaFactory = new PizzaFactory();
            IProductFactory toycarFactory = new ToyCarFactory();
            WrapFactory wrapFactory = new WrapFactory();
            Box box1 = wrapFactory.WrapProduct(pizzaFactory);
            Box box2 = wrapFactory.WrapProduct(toycarFactory);
            Console.WriteLine(box1.Product.Name);
            Console.WriteLine(box2.Product.Name);
        }
    }
    interface IProductFactory //声明一个接口,接口只有一个方法
    {
        Product Make();
    }
    class PizzaFactory : IProductFactory //这个类是Pizaa加工工厂，实现了IProductFactory接口
    {
        public Product Make()
        {
            Product product = new Product();
            product.Name = "Pizza";
            return product;
        }
    }
    class ToyCarFactory : IProductFactory 
    {
        public Product Make()
        {
            Product product = new Product();
            product.Name = "Toy Car";
            return product;
        }
    }
    class Product //产品
    {
        public string Name { get; set; }
    }
    class Box  //包装产品的盒子
    {
        public Product Product { get; set; }
    }
    class WrapFactory //把产品包上盒子交给用户
    {
        public Box WrapProduct(IProductFactory productFactory)
        {
            Box box = new Box();
            Product product = productFactory.Make();
            box.Product = product;
            return box;
        }
    }