Code Like a Ninja Session 7 - Creational Design Patterns

CODE LIKE A NINJA
CREATIONAL DESIGN PATTERNS

SESSION RESOURCES
• Presentation session notes including link to this session, will be available on
http://learningaboutfudge.blogspot.com
• All the source for this session is publically available at:
https://github.com/SheepWorx/Training
• RSS Feed:
http://learningaboutfudge.blogspot.com/feeds/posts/default?alt=rss
• Local Network: dmeyer-msharetrainingCode Like a Ninja
• Source was compiled using Visual Studio 2012
• http://www.gofpatterns.com/

Design Patterns
Creational Design Patterns
Structural Design Patterns
Behavioral Design Patterns

Definition
Creational design patterns are design patterns that deal with object
creation mechanisms, trying to create objects in a manner suitable to
the situation.

• Abstract Factory
• Builder
• Factory Method
• Prototype
• Singleton

FACTORY (ABSTRACT AND METHOD)
• Lets a class defer instantiation into subclasses
• Allows you to introduce new classes without modifying the code
• Factory Method: when you need to delegate the creation of single
objects
• Abstract Factory: When you need to delegate the creation of families
of related or dependant objects without specifying the concrete
classes

SIMPLE FACTORY
Client Factory
Concrete
Class 1
Concrete
Class 2
Concrete
Class 2
Base
class/
interface

SIMPLE FACTORY
• Classes that need to be instantiated need to inherit from a common
class (abstract class or interface)
• The factory will receive some form of identifier and create the correct
concrete class
• Will return it via its base class (abstract class or interface)

SIMPLE FACTORY
See simple factory code example
Question(s):
What will happen when we need to add new types

FACTORY METHOD
Client
Concrete
Factory 1
Concrete
Factory 2
Base
Factory
Concrete
Class 1
Concrete
Class 2
Base
class/
interface

FACTORY METHOD
• Classes you want to create must inherit from a base object (abstract class or
interface)
• Each class will have its own factory
• The factories themselves will inherit off a base factory (abstract class)
• Base factory will control behaviour while individual factories will be
responsible for returning concrete instances of the desired class
• If unique logic exists for a particular class, I recommend it be encapsulated
within its factory

FACTORY METHOD – WHEN TO USE IT
It should be used when…
• A class cannot anticipate the class of objects it must create
• A class wants it subclasses to specify the objects it creates
• Classes delegate responsibility to one of several helper classes and
you want to localize the knowledge of which helper subclass is the
delegate

FACTORY METHOD – BENEFITS
• Eliminates the need to bind application classes to your code
The code only deals with the interface
• Enables subclasses to provide an extended version of an object
because creating an object inside a class is more flexible than
creating the object directly in the client

FACTORY METHOD
See factory method code example

ABSTRACT FACTORY
Client
Abstract
Factory
Abstract
Product A
Abstract
Product B
Concrete
Factory 1
Concrete
Factory 2 Product A2
Product
B2
Product
B1
Product A1

ABSTRACT FACTORY
• Provides an interface for creating families of related or dependant
objects without specifying their concrete classes
• The client interacts only with the product interfaces and the abstract
factory class. It thus never knows about the concrete construction
provided by this pattern
• Abstract factory is similar to the factory method, except it creates
families of related objects.

ABSTRACT FACTORY – WHEN TO USE IT
It should be used when…
• The system should be independent of how its products are created,
composed and represented
• The system should be configured with one of multiple families of
products
• The family of related product objects is designed to be used together
and you must enforce this constraint.

ABSTRACT FACTORY– BENEFITS
• Isolates concrete classes
• Makes exchanging product families easy
• Promotes consistency among products

ABSTRACT FACTORY
See abstract factory code example

Code Like a Ninja Session 7 - Creational Design Patterns

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