Декоратор (Decorator)

Также известен как Обертка (Wrapper).

Паттерн Декоратор динамически наделяет объект новыми возможностями и является гибкой альтернативой субклассированию в области расширения функциональности.

UML

Component - абстрактный компонент
ConcreteComponent - конкретный компонент
Decorator - абстрактный декоратор
ConcreteDecorator - конкретный декоратор

Статья на Википедии

Абстрактная реализация на C# (GoF)

    /// <summary>
    /// MainApp startup class for Structural
    /// Decorator Design Pattern.
    /// </summary>
    internal class MainApp
    {
        /// <summary>
        /// Entry point into console application.
        /// </summary>
        private static void Main()
        {
            // Create ConcreteComponent and two Decorators
            ConcreteComponent c = new ConcreteComponent();
            ConcreteDecoratorA d1 = new ConcreteDecoratorA();
            ConcreteDecoratorB d2 = new ConcreteDecoratorB();

            // Link decorators
            d1.SetComponent(c);
            d2.SetComponent(d1);

            d2.Operation();

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

    /// <summary>
    /// The 'Component' abstract class
    /// </summary>
    internal abstract class Component
    {
        public abstract void Operation();
    }

    /// <summary>
    /// The 'ConcreteComponent' class
    /// </summary>
    internal class ConcreteComponent : Component
    {
        public override void Operation()
        {
            Console.WriteLine("ConcreteComponent.Operation()");
        }
    }

    /// <summary>
    /// The 'Decorator' abstract class
    /// </summary>
    internal abstract class Decorator : Component
    {
        protected Component component;

        public void SetComponent(Component component)
        {
            this.component = component;
        }

        public override void Operation()
        {
            if (component != null)
            {
                component.Operation();
            }
        }
    }

    /// <summary>
    /// The 'ConcreteDecoratorA' class
    /// </summary>
    internal class ConcreteDecoratorA : Decorator
    {
        public override void Operation()
        {
            base.Operation();
            Console.WriteLine("ConcreteDecoratorA.Operation()");
        }
    }

    /// <summary>
    /// The 'ConcreteDecoratorB' class
    /// </summary>
    internal class ConcreteDecoratorB : Decorator
    {
        public override void Operation()
        {
            base.Operation();
            AddedBehavior();
            Console.WriteLine("ConcreteDecoratorB.Operation()");
        }

        private void AddedBehavior()
        {
        }
    }

Реальная реализация на C# (GoF)

    /// <summary>
    /// MainApp startup class for Real-World
    /// Decorator Design Pattern.
    /// </summary>
    internal class MainApp
    {
        /// <summary>
        /// Entry point into console application.
        /// </summary>
        private static void Main()
        {
            // 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();
        }
    }

    /// <summary>
    /// The 'Component' abstract class
    /// </summary>
    internal abstract class LibraryItem
    {
        private int numCopies;

        // Property
        public int NumCopies
        {
            get { return numCopies; }
            set { numCopies = value; }
        }

        public abstract void Display();
    }

    /// <summary>
    /// The 'ConcreteComponent' class
    /// </summary>
    internal class Book : LibraryItem
    {
        private string author;
        private string title;

        // Constructor
        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);
        }
    }

    /// <summary>
    /// The 'ConcreteComponent' class
    /// </summary>
    internal class Video : LibraryItem
    {
        private string director;
        private string title;
        private int playTime;

        // Constructor
        public Video(string director, string title, int numCopies, int playTime)
        {
            this.director = director;
            this.title = title;
            this.NumCopies = numCopies;
            this.playTime = playTime;
        }

        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);
        }
    }

    /// <summary>
    /// The 'Decorator' abstract class
    /// </summary>
    internal abstract class Decorator : LibraryItem
    {
        protected LibraryItem libraryItem;

        // Constructor
        public Decorator(LibraryItem libraryItem)
        {
            this.libraryItem = libraryItem;
        }

        public override void Display()
        {
            libraryItem.Display();
        }
    }

    /// <summary>
    /// The 'ConcreteDecorator' class
    /// </summary>
    internal class Borrowable : Decorator
    {
        protected List<string> borrowers = new List<string>();

        // Constructor
        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);
            }
        }
    }

Улучшенная реальная реализация на C# (GoF)

    /// <summary>
    /// MainApp startup class for .NET optimized
    /// Decorator Design Pattern.
    /// </summary>
    internal class MainApp
    {
        /// <summary>
        /// Entry point into console application.
        /// </summary>
        private static void Main()
        {
            // Create book
            var book = new Book("Worley", "Inside ASP.NET", 10);
            book.Display();

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

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

            var borrow = new Borrowable<Video>(video);
            borrow.BorrowItem("Customer #1");
            borrow.BorrowItem("Customer #2");

            borrow.Display();

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

    /// <summary>
    /// The 'Component' abstract class
    /// </summary>
    internal abstract class LibraryItem<T>
    {
        // Each T has its own NumCopies
        public static int NumCopies { get; set; }

        public abstract void Display();
    }

    /// <summary>
    /// The 'ConcreteComponent' class
    /// </summary>
    internal class Book : LibraryItem<Book>
    {
        private string author;
        private string title;

        // Constructor
        public Book(string author, string title, int numCopies)
        {
            this.author = author;
            this.title = title;
            NumCopies = numCopies;
        }

        public override void Display()
        {
            Console.WriteLine("\nBook ------ ");
            Console.WriteLine(" Author: {0}", author);
            Console.WriteLine(" Title: {0}", title);
            Console.WriteLine(" # Copies: {0}", NumCopies);
        }
    }

    /// <summary>
    /// The 'ConcreteComponent' class
    /// </summary>
    internal class Video : LibraryItem<Video>
    {
        private string director;
        private string title;
        private int playTime;

        // Constructor
        public Video(string director, string title,
            int numCopies, int playTime)
        {
            this.director = director;
            this.title = title;
            NumCopies = numCopies;
            this.playTime = playTime;
        }

        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);
        }
    }

    /// <summary>
    /// The 'Decorator' abstract class
    /// </summary>
    internal abstract class Decorator<T> : LibraryItem<T>
    {
        private LibraryItem<T> libraryItem;

        // Constructor
        public Decorator(LibraryItem<T> libraryItem)
        {
            this.libraryItem = libraryItem;
        }

        public override void Display()
        {
            libraryItem.Display();
        }
    }

    /// <summary>
    /// The 'ConcreteDecorator' class
    /// </summary>
    internal class Borrowable<T> : Decorator<T>
    {
        private List<string> borrowers = new List<string>();

        // Constructor
        public Borrowable(LibraryItem<T> libraryItem)
            : base(libraryItem)
        {
        }

        public void BorrowItem(string name)
        {
            borrowers.Add(name);
            NumCopies--;
        }

        public void ReturnItem(string name)
        {
            borrowers.Remove(name);
            NumCopies++;
        }

        public override void Display()
        {
            base.Display();
            borrowers.ForEach(b => Console.WriteLine(" borrower: " + b));
        }
    }

Реализация на C# (Head First)

    internal class StarbuzzCoffee
    {
        private static void Main(string[] args)
        {
            Beverage beverage = new Espresso();

            Console.WriteLine(beverage.Description
                + " $" + beverage.Cost);

            Beverage beverage2 = new DarkRoast();
            beverage2 = new Mocha(beverage2);
            beverage2 = new Mocha(beverage2);
            beverage2 = new Whip(beverage2);
            Console.WriteLine(beverage2.Description
                + " $" + beverage2.Cost);

            Beverage beverage3 = new HouseBlend();
            beverage3 = new Soy(beverage3);
            beverage3 = new Mocha(beverage3);
            beverage3 = new Whip(beverage3);
            Console.WriteLine(beverage3.Description
                + " $" + beverage3.Cost);

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

    #region Beverage

    public class Beverage
    {
        public virtual string Description { get; protected set; }
        public virtual double Cost { get; protected set; }
    }

    public class DarkRoast : Beverage
    {
        public DarkRoast()
        {
            Description = "Dark Roast Coffee";
            Cost = 0.99;
        }
    }

    public class Decaf : Beverage
    {
        public Decaf()
        {
            Description = "Decaf Coffee";
            Cost = 1.05;
        }
    }

    public class Espresso : Beverage
    {
        public Espresso()
        {
            Description = "Espresso";
            Cost = 1.99;
        }
    }

    public class HouseBlend : Beverage
    {
        public HouseBlend()
        {
            Description = "House Blend Coffee";
            Cost = 0.89;
        }
    }

    #endregion Beverage

    #region CondimentDecorator

    public abstract class CondimentDecorator : Beverage
    {
    }

    public class Whip : CondimentDecorator
    {
        private Beverage _beverage;

        public Whip(Beverage beverage)
        {
            this._beverage = beverage;
        }

        public override string Description
        {
            get { return _beverage.Description + ", Whip"; }
        }

        public override double Cost
        {
            get { return .10 + _beverage.Cost; }
        }
    }

    public class Milk : CondimentDecorator
    {
        private Beverage _beverage;

        public Milk(Beverage beverage)
        {
            this._beverage = beverage;
        }

        public override string Description
        {
            get { return _beverage.Description + ", Milk"; }
        }

        public override double Cost
        {
            get { return .10 + _beverage.Cost; }
        }
    }

    public class Mocha : CondimentDecorator
    {
        private Beverage _beverage;

        public Mocha(Beverage beverage)
        {
            this._beverage = beverage;
        }

        public override string Description
        {
            get { return _beverage.Description + ", Mocha"; }
        }

        public override double Cost
        {
            get { return .20 + _beverage.Cost; }
        }
    }

    public class Soy : CondimentDecorator
    {
        private Beverage _beverage;

        public Soy(Beverage beverage)
        {
            this._beverage = beverage;
        }

        public override string Description
        {
            get { return _beverage.Description + ", Soy"; }
        }

        public override double Cost
        {
            get { return .15 + _beverage.Cost; }
        }
    }

    #endregion CondimentDecorator

Реализация на JAVA

    TODO

Developer-Knowledge-Base

Техническая автобиография и попытка систематизировать знания 📚

Декоратор (Decorator)

Абстрактная реализация на C# (GoF)

Реальная реализация на C# (GoF)

Улучшенная реальная реализация на C# (GoF)

Реализация на C# (Head First)

Реализация на JAVA