Allowing cast between non-related class and interface

Question

4.00/5 (4 votes)

See more:

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

C#

public interface A
{
}

public class B
{
}

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

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?

Posted 16-Dec-10 4:19am

RanCohen

Updated 16-Dec-10 4:35am

Toli Cuturicu

v2

Add a Solution

Comments

Toli Cuturicu 16-Dec-10 10:33am

Interview or homework? Either way, CodeProject is the wrong place to ask this!

RanCohen 16-Dec-10 14:18pm

None of the above - I got a ClassCastException in my program and couldn't figure out why the compiler didn't block me in the first place...
And why is CodeProject the wrong place to ask this?

Toli Cuturicu 18-Dec-10 17:46pm

The CodeProject members ususally do not like to answer what seems to be homework or interview questions.

1 solution

Add a Solution

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

E.F. Nijboer · Accepted Answer · 2010-12-16T04:34:00

Solution 1

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!

Posted 16-Dec-10 4:34am

E.F. Nijboer

Comments

RanCohen 16-Dec-10 14:18pm

That makes sense, thanks!

Allowing cast between non-related class and interface

1 solution

Solution 1

Add your solution here

Preview 0

Allowing cast between non-related class and interface

1 solution

Solution 1

Add your solution here

Preview 0

Existing Members

...or Join us