using System;

public class Program

{

    public static void Main()

    {

        IClass face = (IClass) new SuperClass();

        Console.WriteLine("## Calling thru interface");

        face.NonVirtualMethod();

        face.VirtualMethod();

        SuperClass instance = new SuperClass();

        Console.WriteLine("Calling thru instance");

        instance.NonVirtualMethod();

        instance.VirtualMethod();

        SubClass subClass = new SuperClass();

        Console.WriteLine("Calling thru subclass");

        subClass.NonVirtualMethod();

        subClass.VirtualMethod(); //THIS ONE GOES TO SubClass.VirtualMethod() because of cast

    }

}

​

public interface IClass 

{

    void NonVirtualMethod();

    void VirtualMethod();

}

​

public class SubClass : IClass

{

    public void NonVirtualMethod()

    {

        Console.WriteLine("SubClass - NonVirtualMethod");

    }

    public virtual void VirtualMethod()

    {

        Console.WriteLine("SubClass - VirtualMethod");

    }

}

​

public class SuperClass : SubClass, IClass

{

    public new void NonVirtualMethod()

    {

        Console.WriteLine("SuperClass - NonVirtualMethod");

    }

    public override void VirtualMethod()

    {

        Console.WriteLine("SuperClass - VirtualMethod");

    }

}