C#，继承和转换.. !! [英] C#, Inheritance and casting..!!

问题描述

using System;
using System.Collections.Generic;
using System.Text;
namespace ConsoleApplication1
{
    class A
    {
    }
    class B:A
    {
    }
    class c
    {
        static void Main(string[] args)
        {
            B obj1 = new A();
        }
    }
}

它会执行?? ..如果没有，..任何人都可以给我确切的答案吗?

Will it execute ??..and if not.. can anyone give me the exact answer ???

推荐答案

如果B是A的子类，那么我认为

obj1 = new B()很好，反之亦然


您可以使用超类来引用子类，但不能使用子类来引用超类


您也许可以进行强制转换

If B is a subclass of A then I think

A obj1 = new B() is fine but not vice versa


you can use a superclass to ref a subclass but not a subclass to ref a superclass


you might be able to cast it though

不，它不会执行.

如果编写A obj1 = new B();，它将执行.

为什么?

因为A 是基类，而B 是扩展B的类.因此，根据OOP，B 是一个A，因为A 在继承层次结构中位于较高位置.因此，始终可以将B 的对象分配给A的引用.但是，相反的情况不会执行.

但是，如果按以下方式强制转换对象，则它将编译，但是不会执行:

No, it won''t execute.

If you write A obj1 = new B();, it will execute.

Why?

Because, A is the base class and B is the class that extends B. So, according to OOP, B "is a" A as A is in upper position in the inheritance hirarchy. So, it is always possible to assign an object of B to a reference of A. But, the opposite wouln''t execute.

However, If you cast the object as follows, then it will compile, but, won''t execute:

B obj1 = (B)new A();

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