Creational Patterns and Abstract Factory

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Creational Patterns and Abstract Factory

• Eddie Hirko
• Nathan Bazzel
• Phuong Ngo
• Martin Stonebraker

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Creational Patterns

• Abstract instantiation process
• System independent of how objects are created
  composed, and represented
• Class creational patterns use inheritance to vary
  class instantiation
• Object creational patterns delegate instantiation
  to another object
• Focus on defining small behaviors and combining
  into more complex ones

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Recurring Themes

• Encapsulate knowledge about which concrete
  classes the system uses
• Hide how instances of these classes are created
  and put together

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Advantages

• Flexibility in what gets created
• Who created it
• How it was created and when
• Configure system with product objects that vary
  in structure and functionality
• Configuration can be static or dynamic
• Create standard or uniform structure

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Examples of Object and Class Creational patterns

• Factory Method
• defines an interface for creating objects, but
  lets subclasses decide which classes to
  instantiate
• Abstract Factory
• provides an interface for creating families of
  related objects without specifying concrete
  classes
• Builder
• separates the construction of a complex object
  from its representation, so the same construction
  process can create different representations
• Prototype
• specifies the kind of objects to instantiate
  using a prototypical instance
• Singleton
• ensures that a class has only one instance, and
  provides a global point of reference to that
  instance

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Creational Pattern Summary

• Use what is flexible for the situation.
• Easy to make changes
• Class creational patterns use inheritance
• Object creational patterns use object

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Abstract Factory

• Abstract Factory Object Creational Pattern
• Provides an interface for creating families of
  related or dependent objects without specifying
  their concrete classes

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Why use Abstract Factory?

• If you want to create sets of objects with varied
  attributes
• If you want to keep the user separate from the
  creation process, for example
• For example, a tool-kit where the user creates
  objects by selecting characteristics

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When to use Abstract Factory

• A system should be independent of how its
  products are created, composed, and represented
• A system should be configured with one of
  multiple families of products
• A family of related product objects is designed
  to be used together and you need to enforce this
  constraint
• You want to provide a class library of products,
  and you want to reveal just their interfaces, not
  their implementations

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• A single instance of Concrete Factory is created
  at run-time
• To create different product objects, clients
  should use a different concrete factory

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Benefits and Liabilities

• Isolates concrete classes
• Makes exchanging product families easy
• Promotes consistency among products
• Supporting new kinds of products is difficult

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Implementation

• Key players
• Abstract Factory
• declares an interface for operation that creates
  abstract product objects
• Concrete Factory
• Implements the operation to create product
  objects
• Abstract Product
• Declares an interface for a type of product
  object
• Concrete Product
• Defines a product object to be created by the
  corresponding concrete factory
• Implements the Abstract Product interface
• Client
• Uses only interfaces declared by Abstract Factory
  and Abstract Product classes

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• Key players
• Abstract Factory
• Phuong
• Concrete Factory
• Martin/Nathan
• Abstract Product
• Generic Candy
• Concrete Product
• Eddie
• Client
• Students/users

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How Abstract Factory works