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ptg ptgC r e a t i o n al P a t t e r n s

Abstract Factory ( 8 7) P r o v i de an interface for creating families of r e l a t ed or d e p e n d e nt

o b j e c ts without specifying their c o n c r e te c l a s s e s .

Builder ( 9 7) S e p a r a te the construction of a c o m p l ex o b j e ct from its representation so

that the s a me construction p r o c e ss can create different r e p r e s e n t a t i o n s .

Factory Method ( 1 0 7) Define an interface f or creating an o b j e c t, b ut l et s u b c l a s s es d e -

c i de w h i ch c l a ss to instantiate. Factory M e t h od l e ts a c l a ss defer instantiation to s u b c l a s s e s .

Prototype ( 1 1 7) S p e c i fy t he kinds of o b j e c ts to c r e a te using a prototypical i n s t a n c e, a nd

create new o b j e c ts by c o p y i ng t h is prototype.

S i n g l e t on ( 1 2 7) Ensure a c l a ss only h as o ne i n s t a n c e, a nd provide a g l o b al point of

a c c e s s to it.

S t r u c t u r al P a t t e r n s

Adapter ( 1 3 9) Convert t he interface of a c l a ss into another interface c l i e n ts e x p e c t.

Adapter l e ts c l a s s es work t o g e t h er that c o u l d n 't o t h e r w i se b e c a u se of incompat-

i b le interfaces.

B r i d ge ( 1 5 1) D e c o u p le an abstraction from i ts implementation so that t he t wo c an vary

i n d e p e n d e n t l y .

C o m p o s i te ( 1 6 3) C o m p o se o b j e c ts into t r ee structures to r e p r e s e nt part-whole hierar-

c h i e s. C o m p o s i te l e ts c l i e n ts treat individual o b j e c ts a nd c o m p o s i t i o ns of o b j e c ts

uniformly.

Decorator ( 1 7 5) Attach additional r e s p o n s i b i l i t i es to an o b j e ct dynamically. Decorators

provide a flexible alternative to s u b c l a s s i ng for extending functionality.

F a c a de ( 1 8 5) Provide a unified interface to a set of interfaces in a s u b s y s t e m. Facade

defines a h i g h e r - l e v el interface that makes the subsystem e a s i er to u s e .

F l y w e i g ht ( 1 9 5) U se s h a r i ng to support l a r ge numbers of fine-grained o b j e c ts effi-

c i e n t l y .

P r o xy ( 2 0 7) P r o v i de a surrogate or p l a c e h o l d er for another o b j e ct to control a c c e ss to

it. ptgB e h a v i o r al P a t t e r n s Chain of Responsibility ( 2 2 3) Avoid coupling the sender of a request to its r e c e i v er by

g i v i ng more than one o b j e ct a c h a n ce to handle the r e q u e s t. C h a in the r e c e i v i ng

objects and pass the request along the chain until an object handles it. Command ( 2 3 3) Encapsulate a request as an o b j e c t, thereby letting you parameter- ize clients with different requests, queue or log requests, and support undoable operations. Interpreter ( 2 4 3) Given a language, define a represention for its grammar along with an interpreter that uses the representation to interpret s e n t e n c es in the language. Iterator ( 2 5 7) Provide a way to a c c e ss the elements of an aggregate object sequentially without e x p o s i ng its underlying representation. Mediator ( 2 7 3) Define an object that encapsulates how a set of o b j e c ts interact. Me-

diator promotes l o o se c o u p l i ng by k e e p i ng o b j e c ts from referring to e a ch o t h er

explicitly, and it lets you vary their interaction independently. Memento ( 2 8 3) Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later. Observer ( 2 9 3) Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. State ( 3 0 5) Allow an object to alter its behavior when its internal state changes. The o b j e ct w i ll appear to c h a n ge i ts c l a s s . Strategy ( 3 1 5) Define a family of algorithms, encapsulate each o n e, and make them

i n t e r c h a n g e a b l e. Strategy l e ts the algorithm vary independently from c l i e n ts that

use it.

Template Method ( 3 2 5) Define the s k e l e t on of an algorithm in an o p e r a t i o n, deferring

some steps to subclasses. Template Method l e ts subclasses redefine certain steps of an algorithm without changing the algorithm's structure. Visitor ( 3 3 1) Represent an operation to be performed on the elements of an object structure. Visitor l e ts you define a new operation without changing the c l a s s es of the elements on which it operates. ptgThis page intentionally left blank ptgD e s i g n Patterns ptgA d d i s o n - W e s l ey P r o f e s s i o n al C o m p u t i ng S e r i e s

Brian W. Kernighan, Consulting Editor

Matthew H. Austern, Generic Programming and the STL: Using and Extending the C++ Standard Template Library

David R. Butenhof, Programming with POSIX® Threads

B r e nt Callaghan, NFS Illustrated

Tom C a r g i l l, C++ Programming Style

W i l l i am R. C h es wick /Steven M. Bellovin/Aviel D. Rubin, Firewalls and Internet Security, Second Edition: Repelling

the Wily Hacker D a v id A. Curry, UNIX® System Security: A Guide for Users and System Administrators S t e p h en C. Dewhurst, C++ Gotchas: Avoiding Common Problems in Coding and Design

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ptgD e s i g n Patterns E l e m e n t s of Reusable Object-Oriented Software

E r i ch G a m ma

R i c h a r d H e l m

R a l p h Johnson

J o h n V l i s s i d e s

Boston • San F r a n c i s co • New York • Toronto • Montreal London • Munich • P a r is • Madrid Capetown • Sidney • Tokyo • Singapore • Mexico City

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Design Patterns : e l e m e n ts of reusable o b j e c t - o r i e n t ed software / Erich Gamma ... [et al.].

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ptgTo Karin - E.G.

To Sylvie

- R.H.

To Faith

-R.J.

To Dru Ann and Matthew

Joshua 24:15b

- J.v. ptgP r a i se for Design Patterns: Elements of Reusable

Object-Oriented Software

" T h is is one of the best written and wonderfully insightful books that I have r e ad in a g r e at l o ng while...this

b o ok e s t a b l i s h es the legitimacy of patterns in the b e st way: not by argument but by example."

- S t an L i p p m a n, C++ Report

" . . . t h is new b o ok by Gamma, Helm, Johnson, and Vlissides promises to have an important and lasting

impact on the d i s c i p l i ne of software design. B e c a u se Design Patterns bills i t s e lf as being c o n c e r n ed with

o b j e c t - o r i e n t ed software a l o n e, I fear that software developers outside the object community may i g n o re it.

This would be a shame. T h is b o ok has s o m e t h i ng for everyone who designs software. All software design-

ers use patterns; understanding better the reusable abstractions of our work can only make us better at i t . "

- Tom D e M a r c o, IEEE Software

" O v e r a l l, I think this b o ok r e p r e s e n ts an extremely valuable and unique contribution to the field because

it captures a wealth of object-oriented design experience in a compact and reusable form. T h is b o ok is

certainly one that I s h a ll turn to often in s e a r ch of powerful object-oriented design i d e a s; after a l l, that's

what r e u se is all about, isn't i t ? " - S a n j iv G o s s a i n, Journal of Object-Oriented Programming

" T h is much-anticipated b o ok lives up to its full year of advance buzz. The metaphor is of an architect's

pattern b o ok filled with t i m e - t e s t e d, usable designs. The authors have chosen 23 patterns from d e c a d es of

o b j e c t - o r i e n t ed e x p e r i e n c e. The b r i l l i a n ce of the b o ok l i es in the discipline represented by that number.

Give a c o py of Design Patterns to every g o od programmer you know who wants to be b e t t e r . " - L a r ry O ' B r i e n, Software Development

" T he s i m p le fact of the matter is that patterns have the potential to permanently a l t er the software

engineering field, catapulting it into the r e a lm of true elegant design. Of the b o o ks to d a te on this subject,

Design Patterns is far and away the best. It is a b o ok to be read, studied, internalized, and l o v e d. The b o ok

will forever change the way you view software." - S t e ve Bilow, Journal of Object-Oriented Programming

"Design Patterns is a powerful book. After a m o d e st investment of time with it, m o st C++ programmers

w i ll be a b le to s t a rt applying i ts " p a t t e r n s" to produce better software. T h is b o ok d e l i v e rs i n t e l l e c t u al

l e v e r a g e: c o n c r e te t o o ls that help us think and express ourselves more effectively. It may fundamentally

change the way you think about programming. - Tom Cargill, C++ Report ptgC o n t e n t s

P r e f a c e xi

F o r e w o r d xiii

Guide to Readers xv

1 Introduction 1

1 . 1 What Is a Design Pattern? 2

1 . 2 Design Patterns in Smalltalk MVC 4

1 . 3 Describing Design Patterns 6

1 . 4 The Catalog of Design Patterns 8

1 . 5 Organizing the Catalog 9

1 . 6 How Design Patterns Solve Design Problems 11

1 . 7 H o w t o Select a Design Pattern 28

1 . 8 H o w t o U s e a Design Pattern 29

2 A Case Study: Designing a D o c u m e n t Editor 33

2 . 1 Design Problems 33

2 . 2 Document Structure 35

2 . 3 Formatting 40

2.4 Embellishing the User Interface . 43

2 . 5 Supporting Multiple Look-and-Feel Standards 47

2 . 6 Supporting Multiple Window Systems 51

2 . 7 User Operations i 58

2 . 8 Spelling Checking and Hyphenation 64

v i i ptgv i i i CONTENTS

2 . 9 Summary 76

D e s i gn P a t t e rn C a t a l og 7 9

3 C r e a t i o n al P a t t e r ns 81

A b s t r a ct F a c t o ry 87

B u i l d er 97

F a c t o ry M e t h od 1 07

Prototype 1 17

S i n g l e t on 1 2 7

D i s c u s s i on of C r e a t i o n al Patterns 1 3 5

4 S t r u c t u r al P a t t e r ns 1 37

quotesdbs_dbs8.pdfusesText_14

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