抽象类继承混淆

Question

I have a D class inherits from C abstract class and writing to console related message. I expect to see "D" on my console window but it writes "B". I think virtual keyword in C class breaks the rule. I didn't understand why. Can anyone explain?

  class Program
{
    static void Main(string[] args)
    {
        A obj = new D();
        obj.Write();
        Console.Read();
    }
}

public abstract class A
{
    public virtual void Write()
    {
        Console.WriteLine("A");
    }
}

public abstract class B : A
{
    public override void Write()
    {
        Console.WriteLine("B");
    }
}

public abstract class C : B
{
    public virtual void Write()
    {
        Console.WriteLine("C");
    }
}

public class D : C
{
    public override void Write()
    {
        Console.WriteLine("D");
    }
}

Answer 1

The problem is that C does not override the function from class A . The compiler gives you a warning the the new keyword is required. If you also use override in class C , it works like you expected.

Or if you replace A obj = new D(); with D obj = new D(); , you would get the same result.

Answer 2

Your compiler already does a pretty good job here if you listen to it:

warning CS0114:

'C.Write()' hides inherited member 'B.Write()'.

To make the current member override that implementation, add the override keyword.

Otherwise add the new keyword.

The fact that you used virtual instead of override on C will result in the default behaviour of new for this method, breaking the inheritance chain.