Subject.NotifyObservers C# (CSharp) Method

    public void NotifyObservers()
    {
        NotifyObservers(null);
    }

        static void Main(string[] args)
        {
            var       s = new Subject();
            IObserver a = new ConcreteObserver("Observer A");
            IObserver b = new ConcreteObserver("Observer B");
            IObserver c = new ConcreteObserver("Observer C");

            s.RegisterObserver(a);
            s.RegisterObserver(b);
            s.RegisterObserver(c);

            Console.WriteLine("Registered 3 observer...");
            Console.WriteLine("Notify all observer:");
            s.NotifyObservers("Hello observers!");

            Console.WriteLine();

            s.UnregisterObserver(b);

            Console.WriteLine("Removed observer B...");
            s.NotifyObservers("Hello observers!");

            Console.WriteLine();
            Console.ReadKey();
        }