这里怎么只能访问类方法？ [英] How here only A class method is accessible ?

问题描述

namespace ConsoleApplication1
{
    class A
    {
        public void Amethod()
        {
            Console.WriteLine("Amethod");
        }
    }

    class B : A
    {
        public new void Bmethod()
        {
            Console.WriteLine("Bmethod");
        }
    }




    class Program
    {
        static void Main()
        {

            A ref2 = new B();

            ref2.Amethod(); // how here only A class method is accessible ? Please explain

            B ref3 = new B();

            ref3.Amethod();
            ref3.Bmethod();

        }
    }
}

在上面的代码中，如何才能访问A类方法？请解释。

In the above code, how here only A class method is accessible? Please explain.

推荐答案

因为您的变量 ref2 被声明为类型A，编译器将只访问A类属性和方法 - 因为尽管你在这种情况下为它分配了一个B实例， ref2 不是一个B.它包含一个B实例，因为你没有改变它，但这可能不会持久。



您可以随意将其更改为A类实例。



有点儿喜欢去购物：A是蔬菜，B是胡萝卜 - 因为胡萝卜是一种蔬菜，你可以把蔬菜放在你的购物清单上，然后带着胡萝卜回来。但你也可以带回土豆，因为那也是一种蔬菜。但是马铃薯不具有胡萝卜所具有的橙色特性，所以你不能说蔬菜有橙色。

Because your variable ref2 is declared as a type A, the compiler will only access A class properties and methods - because despite you assigning a B instance to it in this case, ref2 is not a B. It contains an instance of B, because you don't change it, but that may not last.

You are perfectly at liberty to change it later to a A class instance.

It's a bit like going shopping: is A is Vegetable and B is Carrot - because a Carrot is a type of Vegetable you can put "Vegetable" on your shopping list and come back with a Carrot. But you could also come back with a Potato, because that is also a Vegetable. But Potato does not have the "Orange colour" property that Carrot does, so you can't say "Vegetable has Orange colour".

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