This document provides an overview of design patterns, including their definitions, benefits, and classifications. Design patterns describe reusable solutions to common software design problems. They make applications more efficient to develop and maintain by preventing reinventing solutions and enabling communication between developers. Patterns are classified into creational, structural, and behavioral types. Creational patterns deal with object creation, structural patterns define relationships between entities, and behavioral patterns address communication between objects. Examples like the factory method, strategy, and proxy patterns are also outlined.

1. Intro to Design Patterns
Funu Joel

2. Overview
★ What design patterns are.
★ Why they are important.
★ Some OO basics and Design Principles
★ Classifications of Design Patterns
★ Examples

3. What are Design Patterns?

4. Definitions
★ A pattern describes a problem which occurs over and
over again in our environment, and then describes the
core of the solution to that problem, in such a way that
you can use this solution a million times. (Alexander,
1977).
★ A design pattern is a general, reusable solution to a
common problem in software design.(gof, 1995).

5. Elements of a pattern design
★ The pattern name
○ It is used to describe a design problem, its solutions and
consequences in a word or two.
★ The problem
○ It describes when to apply the pattern.
★ The solution
○ It describes the elements that make up the design, their
relationships, responsibilities and collaborations
★ The consequences.
○ the results an tradeoffs of applying the pattern

6. Why are they important?

7. Benefits of design patterns
★ They provide proven solutions to software
development issues.
★ They make communications between
developers more efficient.
★ They make it easier to change and maintain
software.

8. Benefits of design patterns
★ They prevent from wasting your time hacking
your way into a solution.
★ They shift your level of thinking to higher
perspective.
★ They enable design efficient and scalable
applications.

9. OO basics and design principles

10. objected oriented basics
★ Abstraction
★ Encapsulation
★ Polymorphism
★ Inheritance

11. object oriented design principles
★ Separate what varies from what stays the
same .
★ Favor composition over inheritance.
★ Always program to interfaces not
implementations.

12. principles cont'd
★ Strive for loosely coupled design between
objects.
★ Classes should be open to extension but
closed for modification.(open-close principle)

13. Classifications of Design Patterns

14. Classifications
★ Creational Design Patterns
★ Behavioural Design Patterns
★ Structural Design Patterns

15. Creational Patterns
“These are design patterns that deal
with object creation mechanisms.”

16. Types of creational patterns
★ Factory method pattern
★ Abstract factory pattern
★ Builder pattern
★ Prototype pattern
★ Singleton pattern

17. Factory method pattern
“ ”

18. UML representation

19. Code representation

20. Behavioral Patterns
“are patterns that identify common
communication patterns between objects and
realize them to increase flexibility in these
communication.”

21. Types of behavioral patterns
★ Strategy
★ Observer
★ State
★ Command
★ Iterator
★ Mediator
★ Memento
★ Template method
★ Visitor

22. Strategy Pattern
“ ”

23. UML representation

24. Structural Patterns
“these are patterns that identify simple
ways to realize relationships between
entities.”

25. Types of structural patterns
★ Adapter
★ Bridge
★ Decorator
★ Composite
★ Facade
★ Flyweight
★ Proxy

26. Proxy Pattern
“allows you to provide an interface to
other objects by creating a wrapper
class as the proxy ”

27. UML representation