Decorator Design Patterns in C#

Decorator: Allows an objects behavior to be altered at runtime.

class Program
    {
        static void Main(string[] args)
        {
            // Create book
            Book book = new Book("Worley", "Inside ASP.NET", 10);
            book.Display();

            // Create video
            Video video = new Video("Spielberg", "Jaws", 23, 92);
            video.Display();

            // Make video borrowable, then borrow and display
            Console.WriteLine("\nMaking video borrowable:");

            Borrowable borrowvideo = new Borrowable(video);
            borrowvideo.BorrowItem("Customer #1");
            borrowvideo.BorrowItem("Customer #2");

            borrowvideo.Display();

            // Wait for user
            Console.ReadKey();
        }
    }

    //Abstract classes
    abstract class LibraryItem
    {
        private int _numCopies;

        public int NumCopies
        {
            get { return _numCopies; }
            set { _numCopies = value; }
        }

        public abstract void Display();
    }

    //Book - class
    class Book : LibraryItem
    {
        private string _author;
        private string _title;
        public Book(string author, string title, int numcopies)
        {
            this._author = author;
            this._title = title;
            this.NumCopies = numcopies;
        }

        public override void Display()
        {
            Console.WriteLine("\nBook ------ ");
            Console.WriteLine(" Author: {0}", _author);
            Console.WriteLine(" Title: {0}", _title);
            Console.WriteLine(" # Copies: {0}", NumCopies);
        }
    }
    //Video - class
    class Video : LibraryItem
    {
        private string _director;
        private string _title;
        private int _playtime;
        public Video(string director, string title, int playtime, int numCopies)
        {
            this._director = director;
            this._playtime = playtime;
            this._title = title;
            this.NumCopies = numCopies;
        }

        public override void Display()
        {
            Console.WriteLine("\nVideo ----- ");
            Console.WriteLine(" Director: {0}", _director);
            Console.WriteLine(" Title: {0}", _title);
            Console.WriteLine(" # Copies: {0}", NumCopies);
            Console.WriteLine(" Playtime: {0}\n", _playtime);
        }
    }


    // The 'Decorator' abstract class
    abstract class Decorator : LibraryItem
    {
        protected LibraryItem libraryItem;
        public Decorator(LibraryItem libraryItem)
        {
            this.libraryItem = libraryItem;
        }
        public override void Display()
        {
            libraryItem.Display();
        }
    }

     //The 'ConcreteDecorator' class
    class Borrowable : Decorator
    {
        protected List<string> borrowers= new List<string>();
        public Borrowable(LibraryItem libraryItem)
            : base(libraryItem)
        { 
        }
        public void BorrowItem(string name)
        {
            borrowers.Add(name);
            libraryItem.NumCopies--;
        }
        public void ReturnItem(string name)
        {
            borrowers.Remove(name);
            libraryItem.NumCopies++;
        }
        public override void Display()
        {
            base.Display();

            foreach (string borrower in borrowers)
            {
                Console.WriteLine(" borrower: " + borrower);
            }
        }

    }