设计模式之抽象工厂

Abstract Factory Design Pattern

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definition  UML diagram  participants

sample code in C#

definition Provide an interface for creating families of related or dependent objects without specifying their concrete classes. Frequency of use:   high

UML class diagram

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participants

    The classes and/or objects participating in this pattern are:

• AbstractFactory  (ContinentFactory)
  • declares an interface for operations that create abstract products
• ConcreteFactory   (AfricaFactory, AmericaFactory)
  • implements the operations to create concrete product objects
• AbstractProduct   (Herbivore, Carnivore)
  • declares an interface for a type of product object
• Product  (Wildebeest, Lion, Bison, Wolf)
  • defines a product object to be created by the corresponding concrete factory
  • implements the AbstractProduct interface
• Client  (AnimalWorld)
  • uses interfaces declared by AbstractFactory and AbstractProduct classes

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sample code in C#

This structural code demonstrates the Abstract Factory pattern creating parallel hierarchies of objects. Object creation has been abstracted and there is no need for hard-coded class names in the client code.

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// Abstract Factory pattern -- Structural example

using System; namespace DoFactory.GangOfFour.Abstract.Structural {    // MainApp test application    class MainApp   {      public static void Main()     {        // Abstract factory #1       AbstractFactory factory1 = new ConcreteFactory1();       Client c1 = new Client(factory1);       c1.Run();        // Abstract factory #2       AbstractFactory factory2 = new ConcreteFactory2();       Client c2 = new Client(factory2);       c2.Run();        // Wait for user input       Console.Read();     }   }    // "AbstractFactory"    abstract class AbstractFactory   {      public abstract AbstractProductA CreateProductA();      public abstract AbstractProductB CreateProductB();   }    // "ConcreteFactory1"    class ConcreteFactory1 : AbstractFactory   {      public override AbstractProductA CreateProductA()     {        return new ProductA1();     }      public override AbstractProductB CreateProductB()     {        return new ProductB1();     }   }    // "ConcreteFactory2"    class ConcreteFactory2 : AbstractFactory   {      public override AbstractProductA CreateProductA()     {        return new ProductA2();     }      public override AbstractProductB CreateProductB()     {        return new ProductB2();     }   }    // "AbstractProductA"    abstract class AbstractProductA   {   }    // "AbstractProductB"    abstract class AbstractProductB   {      public abstract void Interact(AbstractProductA a);   }    // "ProductA1"    class ProductA1 : AbstractProductA   {   }    // "ProductB1"    class ProductB1 : AbstractProductB   {      public override void Interact(AbstractProductA a)     {       Console.WriteLine( this.GetType().Name +         " interacts with " + a.GetType().Name);     }   }    // "ProductA2"    class ProductA2 : AbstractProductA   {   }    // "ProductB2"    class ProductB2 : AbstractProductB   {      public override void Interact(AbstractProductA a)     {       Console.WriteLine( this.GetType().Name +         " interacts with " + a.GetType().Name);     }   }    // "Client" - the interaction environment of the products    class Client   {      private AbstractProductA AbstractProductA;      private AbstractProductB AbstractProductB;      // Constructor      public Client(AbstractFactory factory)     {       AbstractProductB = factory.CreateProductB();       AbstractProductA = factory.CreateProductA();     }      public void Run()     {       AbstractProductB.Interact(AbstractProductA);     }   } }

Output ProductB1 interacts with ProductA1 ProductB2 interacts with ProductA2

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This real-world code demonstrates the creation of different animal worlds for a computer game using different factories. Although the animals created by the Continent factories are different, the interactions among the animals remain the same.

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// Abstract Factory pattern -- Real World example