Transcript Design Patterns

Design Patterns
Introduction
What is a Design Pattern?
Why were they developed?
Why should we use them?
How important are they?
How easy are they to use?
Resources
[email protected]
Design Patterns
What is a Design Pattern?
When programming complex systems, some
problems arise again and again.
Programmers build up expertise and
experience of solving these problems.
A design pattern can be thought of as an
encapsulation of programming “best practice”.
Languages like Java already incorporate
some design patterns into their structure.
[email protected]
Design Patterns
What is a Design Pattern?
A design pattern is not necessarily a single
chunk of code (detailed implementation).
It may be a style, an approach to solving a
problem (architecture).
It may be the “best” approach - one that
experience has shown to be efficient, reliable,
scalable and so on.
Many patterns come with UML documentation.
[email protected]
Design Patterns
What is a Design Pattern?
“Design patterns constitute a set of rules
describing how to accomplish certain tasks in
the realm of software development.” (Pree,
1994)
“Design patterns focus more on reuse of
recurring architectural design themes, while
frameworks focus on detailed design… and
implementation.” (Coplien & Schmidt, 1995).
[email protected]
Design Patterns
What is a Design Pattern?
“A pattern addresses a recurring design
problem that arises in specific design
situations and presents a solution to it”
(Buschmann, et. al. 1996)
“Patterns identify and specify abstractions that
are above the level of single classes and
instances, or of components.” (Gamma, et al.,
1993)
[email protected]
Design Patterns
Why were they developed?
Attempts to make programming into an
engineering discipline rather than an art form.
Can help to keep costs low.
Brings reliability through good design.
Speeds development cycles since no need to
“reinvent the wheel”.
Helps with maintenance (patterns may get
updated).
[email protected]
Design Patterns
Why should we use them?
Design Patterns should help us achieve our
development goals with less effort.
Communities of programmers will have
familiarity with common patterns.
Modern languages incorporate some patterns
at the API level, for example the Java media
loading and event handling systems.
[email protected]
Design Patterns
How important are they?
In some areas (finance, engineering, user
interface design) they are very useful and
widely used.
For some small, ad-hoc, single-developer
projects, most of the more complex and
specialised design patterns may not have
much impact.
[email protected]
Design Patterns
How easy are they to use?
Some design patterns are very simple to use,
others are complex solutions to specific,
complex problems.
You probably use some already – the Swing
graphics framework is based in part on wellknown design patterns.
They are well documented and explained.
Books of patterns exist – a limited number of
patterns have been found
[email protected]
Design Patterns
Resources
 Design Patterns Java Companion (free book in PDF format):
http://www.patterndepot.com/put/8/JavaPatterns.htm
 Example patterns with explanatory text, Antonio García:
http://www.exciton.cs.rice.edu/JavaResources/DesignPatterns/defa
ult.htm
 Sun J2EE Patterns: http://java.sun.com/blueprints/patterns/
 Java Design Patterns 201: http://www106.ibm.com/developerworks/edu/j-dw-javapatt2-i.html
 Core J2EE Patterns (book on Amazon)
 Important book: Design Patterns by Gamma, Helm, Johnson and
Vlissides (Addison Wesley Longman, 1995. ISBN 0-201-63361-2)
 Interesting review of the above book here.
[email protected]
Design Patterns
Conclusion
Design patterns are worth using in many
circumstances.
You will have to invest some time in order to
understand them and absorb the implications
of this style of programming.
For corporate developers, design patterns
represent a resource of expertise that cannot
be ignored.
[email protected]