The Factory Method Pattern defines an interface for creating an object, but lets subclasses decide which class to instantiate.
A factory method
- handles object creation and
- encapsulates it in a subclass.
Definition
// A facotry method
// 1. is abstract so the subclass are counted on to handle object creation.
// 2. returns a Product.
// 3. isolates the client from knowing what of concrete Product is actually created.
// 4. may be parameterized (or not) to select among several variations of a product.
protected abstract Pizza CreatePizza(PizzaType type);
Usage
PizzaStore americanStore = new AmericanPizzaStore();
Pizza pizza = americanStore.OrderPizza(PizzaType.Veggie);
Console.WriteLine("Esposito ordered a " + pizza.Name);
// Italian Pizza Store
PizzaStore italianStore = new ItalianPizzaStore();
Pizza pizza = italianStore.OrderPizza(PizzaType.Cheese);
Console.WriteLine("Esposito ordered a " + pizza.Name);
- Product (Pizza)
- defines the interface of objects the factory method creates
- ConcreteProduct (ItalianCheesePizza, AmericanCheesePizza etc.)
- implements the Product interface
- Creator (PizzaStore)
- declares the abstract factory method which returns an instance of type Product.
- may call the factory method to return an instance (OrderPizza calls CreatePizza)
- ConcreteCreator(AmericanPizzaStore)
- overrides the abstract factory method to return an instance of a ConcreteProduct (eg. AmericanCheesePizza)
[Source: http://www.dofactory.com/net/factory-method-design-pattern]