using System;

​

public class Logger

{

    public virtual void Log(string message)

    {

        // actually do nothing

    }

}

​

public class ConsoleLogger : Logger

{

    public override void Log(string message)

    {

        Console.WriteLine(message);

    }

}

​

public class FileLogger : Logger

{

    public override void Log(string message)

    {

        // log to file

    }

}

public class Program

{

    public static void Main()

    {

        Logger logger = new ConsoleLogger();

​

        logger.Log("Hello, world from ConsoleLogger!");

    }

}

​