using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        List<ISample> lst = new List<ISample>();

        lst.Add(new First("Hello"));

        lst.Add(new Second("World"));

        foreach (ISample x in lst){

            x.Write();

        }

    }

}

​

public interface ISample

{

    string str {get;set;}

    void Write();

}

​

public class First : ISample

{

    public string str {get;set;}

    public First(string str){

        this.str = str;

        }

    public void Write()

    {

        Console.WriteLine(this.str);

    }

}

​

public class Second : ISample

{

    public string str {get;set;}

    public Second(string str){

        this.str = str;

        }

    public void Write()

    {

        Console.WriteLine(this.str);

    }

}

​