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Posted on 3:29 AM by Softminer and filed under ,

Define an interface for creating an object, but let subclasses decide which class to instantiate. Factory Method lets a class defer instantiation to subclasses.

// Factory Method pattern -- Structural example

using System;
 
namespace DoFactory.GangOfFour.Factory.Structural
{
  /// <summary>
  /// MainApp startup class for Structural
  /// Factory Method Design Pattern.
  /// </summary>
  class MainApp
  {
    /// <summary>
    /// Entry point into console application.
    /// </summary>
    static void Main()
    {
      // An array of creators
      Creator[] creators = new Creator[2];
 
      creators[0] = new ConcreteCreatorA();
      creators[1] = new ConcreteCreatorB();
 
      // Iterate over creators and create products
      foreach (Creator creator in creators)
      {
        Product product = creator.FactoryMethod();
        Console.WriteLine("Created {0}",
          product.GetType().Name);
      }
 
      // Wait for user
      Console.ReadKey();
    }
  }
 
  /// <summary>
  /// The 'Product' abstract class
  /// </summary>
  abstract class Product
  {
  }
 
  /// <summary>
  /// A 'ConcreteProduct' class
  /// </summary>
  class ConcreteProductA : Product
  {
  }
 
  /// <summary>
  /// A 'ConcreteProduct' class
  /// </summary>
  class ConcreteProductB : Product
  {
  }
 
  /// <summary>
  /// The 'Creator' abstract class
  /// </summary>
  abstract class Creator
  {
    public abstract Product FactoryMethod();
  }
 
  /// <summary>
  /// A 'ConcreteCreator' class
  /// </summary>
  class ConcreteCreatorA : Creator
  {
    public override Product FactoryMethod()
    {
      return new ConcreteProductA();
    }
  }
 
  /// <summary>
  /// A 'ConcreteCreator' class
  /// </summary>
  class ConcreteCreatorB : Creator
  {
    public override Product FactoryMethod()
    {
      return new ConcreteProductB();
    }
  }
}
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