Code Like a Ninja Session 7 - Creational Design Patterns
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CODE LIKE A NINJA CREATIONAL DESIGN PATTERNS
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presentation on some creational design patterns namely the factory method and the abstract factory
Transcript of Code Like a Ninja Session 7 - Creational Design Patterns
CODE LIKE A NINJACREATIONAL 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-m\share\training\Code Like a Ninja
• Source was compiled using Visual Studio 2012
• http://www.gofpatterns.com/
Design Patterns
Creational Design PatternsStructural Design PatternsBehavioral Design Patterns
CREATIONAL 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
CREATIONAL DESIGN PATTERNS
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 codeThe 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 FACTORYClient
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
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-m\share\training\Code Like a Ninja
• Source was compiled using Visual Studio 2012
• http://www.gofpatterns.com/
