Java继承与C＃继承 [英] Java inheritance vs. C# inheritance

问题描述

让我们说Java有这些层次的类：

Let's say Java has these hierarchical classes:

class A 
{
}
class B extends A
{
    public void m()
    {
        System.out.println("B\n");
    }
}
class C extends B
{
    public void m()
    {
        System.out.println("C\n");
    }
}
class D extends C
{
    public static void main(String[] args)
    {
        A a = new D();
        // a.m(); // doesn't work
        B b = new D();
        b.m();
        C c = new D();
        c.m();
        D d = new D();
        d.m();
    }
}

这是相同的代码的（盲）的重复在C＃中：

This is the (blind) duplication of the same code in C#:

using System;
class A 
{   
}
class B : A
{
    public void M()
    {
        Console.WriteLine("B");
    }
}
class C : B
{
    public void M() // I need to use public new void M() to avoid the warning
    {
        Console.WriteLine("C");
    }
}
class D : C
{
    public static void Main(String[] args)
    {
        A a = new D();
        // a.M(); // doesn't work       
        B b = new D();
        b.M();
        C c = new D();
        c.M();
        D d = new D();
        d.M();
    }
}

当我执行Java代码，我得到了 CCC ，而C＃返回 BCC 。

When I execute the Java code, I got C-C-C whereas C# returns B-C-C.

要我丙的＃结果令更有意义，作为参考b调用它自己的方法。

To me C#'s result makes more sense, as reference B invokes its own method.

• 什么是Java的设计者决定打印 CCC背后的逻辑而不是 BCC ？我的意思是，为什么参照B使用在C重写的方法？什么是这种方法的优势在哪里？


• 如何更改Java代码来打印出 B-C-C 就像C＃呢？我的意思是，我怎么能教的java调用它采用了精确的参考值的方法？


• 我怎样才能改变C＃代码打印出来 CCC ？我的意思是，我怎么能教C＃调用覆盖方法？

• What's the logic behind the Java designer's decision to print C-C-C instead of B-C-C? I mean, why reference B uses the overriding method in C? What's the advantage of this approach?
• How can I change Java code to print out B-C-C just like C# does? I mean, how can I teach java to invoke the method of the exact reference it uses?
• How can I change C# code to print out C-C-C? I mean, how can I teach C# to invoke the overriding method?

推荐答案

这对虚函数定义：

一个虚函数或虚方法是一个函数或方法，其行为可以继承类内的函数具有相同签名的覆盖。这个概念是面向对象编程（OOP）的多态性部分的一个非常重要的组成部分。

a virtual function or virtual method is a function or method whose behavior can be overridden within an inheriting class by a function with the same signature. This concept is a very important part of the polymorphism portion of object-oriented programming (OOP).

在C＃中，你应该申报方法以虚拟被重写，如图MSDN：

In C#,you should declare the method as virtual in order to be overriden, as shown in MSDN:

• 的10.5.3虚方法（这是从2003年VS，但它是最新的）


• C＃虚拟

• 10.5.3 Virtual methods (it's from VS 2003, but it's up to date)
• C# Virtual

由于在 M 方法不是虚拟的，它会执行 BM（）即使 b 变量实际上是一个 D 实例。

Since the M method is not virtual, it will execute b.M() even if b variable is actually a D instance.

在Java中，每一个方法是通过默认虚拟，所以，当你覆盖方法（即使没有 @覆盖注释）的行为 BM（）将在 DM（）继承了 CM（）法的行为。

In Java, every method is virtual by default, so you when you override a method (even without the @Override annotation) the behavior of the b.M() will be the d.M() that inherits the c.M() method behavior.

如何更改Java代码打印出来BCC就像C＃呢？我的意思是，我怎么能教的java调用它采用了精确的参考值的方法？

How can I change Java code to print out B-C-C just like C# does? I mean, how can I teach java to invoke the method of the exact reference it uses?

您根本无法做到这一点的Java的。在 C中的 M 法类将重写 M 方法在 B 。添加最后修改为 B＃m的将只是使 C 或其他 b 儿童不能覆盖 M（）方法。

You simply can't do this in Java. The M method in C class would override the M method in B. Adding the final modifier to B#M will just make that C or other B children can't override the M() method.

我怎样才能改变C＃代码打印出来CCC？我的意思是，我怎么能教C＃调用覆盖方法？

How can I change C# code to print out C-C-C? I mean, how can I teach C# to invoke the overriding method?

更改 M 方法 B 类虚拟和 C 类：

class B : A
{
    public virtual void M()
    {
        Console.WriteLine("B");
    }
}
class C : B
{
    public override void M() // I need to use public new void M() to avoid the warning
    {
        Console.WriteLine("C");
    }
}

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