using System;

public class Program

{

    public static void Main()

    {

        var context = new Context(new RegularDuck());

        context.DoDuckStuff();

​

        context = new Context(new DonaldDuck());

        context.DoDuckStuff();

​

        context = new Context(new RubberDuck());

        context.DoDuckStuff();

​

        context = new Context(new DecoyDuck());

        context.DoDuckStuff();

    }

​

    class Context

    {

        private Duck _duck;

​

        public Context(Duck duck)

        {

            _duck = duck;

        }

​

        public void DoDuckStuff()

        {

            _duck.Display();                

            _duck.Quack();                

            _duck.Swim();                

            _duck.Fly();

            Console.WriteLine("\n\n");

        }

    }

​

    abstract class Duck

    {

        public abstract void Display();

​

        public virtual void Quack()

        {

            Console.WriteLine("Quack! Quack!");

        }

​

        public void Swim()

        {

            Console.WriteLine("Duck is swimming");

        }

​

        // New Feature

        public virtual void Fly()

        {

            Console.WriteLine("Duck is flying");

        }

    }

​

    class RegularDuck : Duck

    {

        public override void Display()

        {

            Console.WriteLine("This is a Regular Duck");

        }

    }

​

    class DonaldDuck : Duck

    {

        public override void Display()

        {

            Console.WriteLine("This is a Donald Duck");

        }

    }

​

    class RubberDuck : Duck

    {

        public override void Display()

        {

            Console.WriteLine("This is a Rubber Duck");

        }

​

        public override void Quack()

        {

            Console.WriteLine("Squick! Squick!");

        }

​

        public override void Fly()

        {

            // Do nothing

        }

    }

​

    class DecoyDuck : Duck

    {

        public override void Display()

        {

            Console.WriteLine("This is a Decoy Duck");

        }

​

        public override void Quack()

        {

            // Do nothing

        }

​

        public override void Fly()

        {

            // Do nothing

        }

    }

}