1. Design Patterns
References: Xiaoping Jia, Object-Oriented Software Development Using Java;Douglas C.Schmidt, Design Pattern Case Studies with C++

2. Design Patterns Generic (reusable) solutions to a recurring problem
Evolved from Christopher Alexander’s patterns for architecture.
“Each 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 over, without ever doing it the same way twice.” – Alexander et. al., A Pattern Language (Oxford U.Press,1977)

3. Design Patterns–a ‘Hot Topic’
OOPSLA Workshops – 17%
Patterns for Software Architecture
Killer Examples for Design Patterns & Objects First
Patterns in Distributed Real Time & Embedded Systems
Patterns for Customer Interaction & Expectation Management
Software Development Process Patterns

4. Design Patterns–a ‘Hot Topic’
OOPSLA Tutorials – 20%
Pattern-oriented Software Architectures for Networked and Concurrent Applications
Patterns of Enterprise Application Architecture
Patterns at Work
Patterns for Writing Effective Use Cases
Dungeons and Patterns!
Patterns and Application Experiences for Real-time Object Request Brokers
Refactoring to Patterns
Object-oriented Reengineering: Patterns & Techniques
Patterns for EJB Development
How to Use Design Patterns in Java and .NET

5. Design Patterns Categories of Software Design Patterns
Creational : deal with process of creation
Structural : deal with static composition and structure of classes and objects
Behavioral : deal with dynamic interaction among classes and objects

6. Design Patterns Each pattern is described as follows: Pattern name
Category : creational, structural or behavioral
Intent : short description of problem addressed
AKA: other names for the pattern
Applicability : where pattern can be applied
Structure : diagram that describes participants in the pattern & relationships among them
Participants : list of classes and/or objects that participate in the pattern

7. Singleton Pattern Category: creational
Intent: ensure that a class has only one instance and provide global point of access to it
Applicability: use where there must be exactly one instance of a class and it must be accessible to clients from a well-known access point (e.g. database)

8. Singleton Pattern Structure Singleton static getInstance()
operation()
getData()
static Singleton theInstance
data
return theInstance

9. Singleton Pattern Participants : only one
Singleton declares the unique instance of the class as a static variable and defines a static method getInstance() for clients to access the unique instance.

10. Singleton Pattern public class Singleton {
public static Singleton getInstance() {
return theInstance; }
private Singleton() {
//initialize instance fields
//….
private static Singleton theInstance = new Singleton();

11. Strategy Pattern Category : behavioral
Intent: define a family of algorithms, encapsulate each one and make them interchangeable

12. Strategy Pattern Applicability: use when
many related classes differ only in behavior
plotting different functions
different variations of algorithm are needed
sorts
an algorithm uses data that clients should not know about
LayoutManager in the AWT
a class defines many behaviors which appear as multiple conditional statements in its methods

13. Structure of Strategy Pattern
Context
contextInterface()
Strategy
algorithmInterface()
Concrete Strategy A
algorithmInterface()
Concrete Strategy C
algorithmInterface()
Concrete Strategy B
algorithmInterface()
Note: arrowheads should be unfilled

14. Using the Strategy Pattern
Pivot Strategy
getPivot()
quicksort
pivotStrategy.getPivot(array,lo,hi)
Random
Median of
Three
Select
First
Concrete
Strategies
Strategy pattern resolves how to extend policies for selecting a
pivot value without modifying main quicksort algorithm

15. A tutorial presented by Steve Metsker and William Wake
Dungeons & Patterns
A tutorial presented by Steve Metsker and William Wake
At OOPSLA 2001

16. Why Design Patterns?
Patterns record previous successes in a reusable form
Design patterns are well-worn solutions to problems at about a class level

17. How the Game Works
Each table has a pattern master who has a map of a dungeon
You must adventure through the dungeon to reclaim pearls of wisdom from a dragon
Your primary helper is an Ahobbit
With capricious magical abilities

18. Ahobbits Your Ahobbit has a magical ring that
Cannot be removed
You can activate by getting him/her to say “Aha”
Ahobbits are enlightened only when they understand a design pattern
Ahobbits learn from real-world examples in the dungeon

19. Adventuring Find a room in the dungeon When you enter
Examine the device or contents therein
Determine which pattern it shows
Use the device to explain to your Ahobbit the intent of the pattern (2 guesses)
When the Ahobbit says “Aha,” something magical will occur

20. Beginning We shall begin as one huge exploration party
Before breaking into one party per table or group
You stand before a door that leads to the dungeon
What do you do?