Factory Method Pattern

• The Factory Method Pattern is being explained
• The kinds of furniture created can be tightly coupled
• It may be necessary to order furniture from a central spot or factory

Definition

• The factory method pattern is a design pattern
• It allows for the creation of objects without the need to specify the type of object being created in code
• A factory class contains a method that allows determination of the created type at run-time
• The factory pattern is a creational pattern
• It is used to control class instantiation
• The factory pattern is used to replace class constructors, abstracting the process of object generation
• It determines the object instantiated at run-time

Intent

• The factory method defines an interface for creating objects
• It allows subclasses to decide which class to instantiate
• The factory refers to the newly created object through a common interface

Benefits

• The factory pattern introduces a separation between the application and a family of classes
• This introduces weak coupling instead of tight coupling, hiding concrete classes from the application
• Provides a simple way of extending the family of products with minor changes in application code
• The factory provides customization hooks
• Replacing objects with others that extend their functionality is difficult if objects are created directly inside the class
• A factory used to create a family of objects allows customized objects to easily replace the originals, configuring the factory to create them

Drawbacks

• The factory needs to be utilized for a family of objects
• The classes can't be used if they don't extend a common base class or interface in a factory design template

Implementation

• The FactoryBase is an abstract base class for concrete factory class that generates new objects
• It may be a simple interface containing the signature for the factory method
• It can be an abstract class for standard functionality to be included and inherited by subclasses
• In simple situations, the factory method may be implemented in full here, rather than being declared as abstract
• The ConcreteFactory inherits the factory method from the FactoryBase class
• This is overriden with object generation code unless already implemented in full in the base class
• The ProductBase is an abstract class
• It acts as the base class for object types that the factory can create
• Return type for the factory method
• It can be a simple interface if no general functionality is to be inherited by subclasses
• The ConcreteProduct includes multiple subclasses of the Product class, each with specific functionality
• Objects of these classes are generated by the factory method