using System;

public class Program

{

    public static void Main()

    {

        BBB bbb = new BBB();

        bbb.MyMethod();

        Console.WriteLine();

        bbb.MyMethod2();

        Console.WriteLine();

        AAA aaa = bbb;

        aaa.MyMethod();

        Console.WriteLine();

        aaa.MyMethod2();

    }

    class AAA

    {

        public virtual void MyMethod(string s = "aaa")

        {

            Console.WriteLine("AAA.MyMethod: " + s);

        }

​

        public virtual void MyMethod2()

        {

            Console.WriteLine("AAA.MyMethod2");

            MyMethod();

        }

    }

​

    class BBB : AAA

    {

        public override void MyMethod(string s = "bbb")

        {

            Console.WriteLine("BBB.MyMethod: " + s);

            base.MyMethod(s);

        }

​

        public override void MyMethod2()

        {

            Console.WriteLine("BBB.MyMethod2");

            MyMethod();

        }

    }

}