Programming - Factory Method Design Pattern

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

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

Productand
- defines the interface of objects the factory method creates
ConcreteProduct
- implements the Product interface
Creatorand
- declares the factory method, which returns an object of type Product. Creator may also define a default implementation of the factory method that returns a default ConcreteProduct object.
- may call the factory method to create a Product object.
ConcreteCreator
- overrides the factory method to return an instance of a ConcreteProduct.

// Factory Method pattern -- Structural example

using

System;
using System.Collections;

namespace DoFactory.GangOfFour.Factory.Structural
{

// MainApp test application

class MainApp
{
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.Read();
}
}

// "Product"

abstract class Product
{
}

// "ConcreteProductA"

class ConcreteProductA : Product
{
}

// "ConcreteProductB"

class ConcreteProductB : Product
{
}

// "Creator"

abstract class Creator
{
public abstract Product FactoryMethod();
}

// "ConcreteCreator"

class ConcreteCreatorA : Creator
{
public override Product FactoryMethod()
{
return new ConcreteProductA();
}
}

// "ConcreteCreator"

class ConcreteCreatorB : Creator
{
public override Product FactoryMethod()
{
return new ConcreteProductB();
}
}
}

Output expected:

              Created ConcreteProductA

               Created ConcreteProductB

and