Essential Elements

1
Essential Elements

• Pattern Name Describe a design problem, its
  solutions, and consequences in a word or two.
• Problem Describes when to apply the pattern.
• Solution Describes the elements that make up
  the design, their relationships,
  responsibilities, and collaborations.
• Consequences The results and trade-offs of
  applying the pattern.

2
Creational Patterns

• Object composition vs. class inheritance
• What gets created?
• Who creates it?
• How it gets created?
• When is it created?

3
Create Mazes
4
Problems with the Initial Code

• Maze layout is hard-coded in a member function.
• Hard to reuse an existing maze layout for
  additional feature of maze.

5
A Scenario for Abstract Factory
6
Abstract Factory
7
Participants

• AbstractFactory declares an interface for
  operations that create abstract product objects.
• ConcreteFactory implements the operations to
  create concrete product objects.
• AbstractProduct declares an interface for a type
  of product object.
• ConcreteProduct defines a product object to be
  created by the corresponding concrete factory and
  implements the AbstractProduct interface.
• Client uses only interfaces declared by
  AbstractFactory and AbstractProduct classes.

8
A Scenario for Factory Method
9
Factory Method
10
Participants

• Product defines the interface of objects the
  factory method creates.
• ConcreteProduct implements the Product interface.
  
• Creator declares the factory method, which
  returns an object of type Product. Creator may
  also define a default implementation of the
  factory method that returns a default
  ConcreteProduct object or call the factory method
  to create a Product object.
• ConcreteCreator overrides the factory method to
  return an instance of a ConcreteProduct.