using System;

public class Program

{

    public static void Main()

    {

        Container c1 = new Container("abc");

        Container c2 = new Container("123");

        Console.WriteLine("####");

        A a = new A() { PublicContainer = c1 };

        a.PrintStuff();

        Console.WriteLine("####");

        B b = new B() { PublicContainer = c2 };

        b.PrintStuff();

        b.PrintDifferentStuff();

        Console.WriteLine("####");

        A ab = new B() { PublicContainer = c2 };

        ab.PrintStuff();

    }

    public class A 

    {

        public Container PublicContainer;

        public void PrintStuff()

        {

            Console.WriteLine("PrintStuff A");

            PrintContainer(PublicContainer);

            Console.WriteLine();

        }

        protected void PrintContainer(Container container)

        {

            bool hasContainer = container is not null;

            string containerValue = container?.Value ?? "?";

            Console.WriteLine($"has container: {hasContainer}, value: {containerValue}");

        }

    }

    public class B : A 

    {

        public new Container PublicContainer;

        public void PrintDifferentStuff()

        {

            Console.WriteLine("PrintStuff B");

            Console.WriteLine("My container:");

            PrintContainer(PublicContainer);

            Console.WriteLine("Base container:");

            PrintContainer(base.PublicContainer);

            Console.WriteLine();

        }

    }

    public class Container 

    { 

        public string Value {get;set;}

        public Container(string value)

        {

            Value = value;

        }

    }

}