允许在不相关的类和接口之间进行强制转换 [英] Allowing cast between non-related class and interface

问题描述

以下代码在Java和C#中编译，我不明白为什么:

The following code compile in java and C# and I can''t understand why:

public interface A
{
}

public class B
{
}

public class C
{
    private void foo(A a)
    {
        B b = (B)a;
    }
}

A与B毫无关系.如果将A更改为class而不是interface，则代码将无法编译.为什么将A声明为interface会改变呢?

A is not related to B in any way. If I change A to be a class instead of an interface the code will not compile. Why does declaring A as an interface change that?

推荐答案

编译时没有错误，因为B的派生类也可以具有已实现的接口A.编译器不会进行检查，但是如果您要对其进行测试并传递例如实现A但不是B的后代的类D，则会出现错误.

祝你好运！

There isn''t an error at compile time because a derived class of B can also have implemented interface A. The compiler doesn''t check that but if you would test it and pass a class D for example that implements A but is not a descendant of B, you would get an error.

Good luck!

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