Object Oriented Design Patterns Opilo | By Hamid Alaee

1. Object Oriented Design
Patterns
Organization
Opilo | By Hamid Alaee

2. Organizing Design Patterns by Purpose (review)
• Creational (5)
• Concerns object creation
• Structural (7)
• Deals with composition of classes or objects
• Behavioral (11)
• Characterizes ways in which classes or objects interact and distribute
responsibility.

3. Organizing Design Pattern by Scope
• Class Patterns (4)
• Deal with relationships between classes and their subclasses
• Relationships established through inheritance, so they are fixed at compile
time (static)
• Inheritance: white-box reuse
• Object patterns (20)
• Deal with object relationships (e.g. composition)
• Relationships can be changed at runtime (dynamic)
• Composition: Black-box reuse, to avoid breaking encapsulation, and
implementation dependency

4. The Catalog of Design Patterns
Scope / purpose Creational Structural Behavioral
Class Factory Method Adapter Interpreter
Template Method
Object Abstract Factory
Builder
Prototype
Singleton
Adapter (object)
Bridge
Composite
Decorator
Façade
Flyweight
Proxy
Chain of Responsibility
Command
Iterator
Mediator
Observer
State
Strategy
Visitor

5. Six types of design patterns
1. Creational class patterns defer some part of object creation to
subclasses
2. Creational object patterns defer some part of object creation to
another object
3. Structural class patterns use inheritance to compose classes
4. Structural object patterns describe ways to assemble objects
5. Behavioral class patterns use inheritance to describe algorithms
and flow of control
6. Behavioral object patterns describe how a group of objects
cooperate to perform a task that no single object can carry out alone

6. Relation between Patterns
• Patterns may be uses together
• Command + Composite => MacroCommand
• Command + Memento => Undoable Command
• Command + Prototype => Copy of Command in the undo history
• Some patterns are alternatives to one another
• Prototype and Abstract Factory are competing patterns in some ways
• Some patterns result in similar design although they have different intents
• Decorator can be viewed as a degenerate Composite with only one component.
• Decorator’s intent: adding additional responsibilities
• Composite’s intent: object aggregation