Design Patterns: Elements of Reusable Object-Oriented Software

420 Pages·1994·17.189 MB·English

by  Gamma, Erich;Johnson, Ralph;Vlissides, John;Helm, Richard

Creational Patterns
Abstract Factory (87) Provide an interface for creating families of related or dependent
objects without specifying their concrete classes.
Builder (97) Separate the construction of a complex object from its representation so
that the same construction process can create different representations.
Factory Method (107) Define an interface for creating an object, but let subclasses de-
cide which class to instantiate. Factory Method lets a class defer instantiation to
subclasses.
Prototype (117) Specify the kinds of objects to create using a prototypical instance, and
create new objects by copying this prototype.
Singleton (127) Ensure a class only has one instance, and provide a global point of
access to it.
Structural Patterns
Adapter (139) Convert the interface of a class into another interface clients expect.
Adapter lets classes work together that couldn't otherwise because of incompat-
ible interfaces.
Bridge (151) Decouple an abstraction from its implementation so that the two can vary
independently.
Composite (163) Compose objects into tree structures to represent part-whole hierar-
chies. Composite lets clients treat individual objects and compositions of objects
uniformly.
Decorator (175) Attach additional responsibilities to an object dynamically. Decorators
provide a flexible alternative to subclassing for extending functionality.
Facade (185) Provide a unified interface to a set of interfaces in a subsystem. Facade
defines a higher-level interface that makes the subsystem easier to use.
Flyweight (195) Use sharing to support large numbers of fine-grained objects effi-
ciently.
Proxy (207) Provide a surrogate or placeholder for another object to control access to
it.
Behavioral Patterns
Chain of Responsibility (223) Avoid coupling the sender of a request to its receiver by
giving more than one object a chance to handle the request. Chain the receiving
objects and pass the request along the chain until an object handles it.
Command (233) Encapsulate a request as an object, thereby letting you parameter-
ize clients with different requests, queue or log requests, and support undoable
operations.
Interpreter (243) Given a language, define a represention for its grammar along with
an interpreter that uses the representation to interpret sentences in the language.
Iterator (257) Provide a way to access the elements of an aggregate object sequentially
without exposing its underlying representation.
Mediator (273) Define an object that encapsulates how a set of objects interact. Me-
diator promotes loose coupling by keeping objects from referring to each other
explicitly, and it lets you vary their interaction independently.
Memento (283) Without violating encapsulation, capture and externalize an object's
internal state so that the object can be restored to this state later.
Observer (293) Define a one-to-many dependency between objects so that when one
object changes state, all its dependents are notified and updated automatically.
State (305) Allow an object to alter its behavior when its internal state changes. The
object will appear to change its class.
Strategy (315) Define a family of algorithms, encapsulate each one, and make them
interchangeable. Strategy lets the algorithm vary independently from clients that
use it.
Template Method (325) Define the skeleton of an algorithm in an operation, deferring
some steps to subclasses. Template Method lets subclasses redefine certain steps
of an algorithm without changing the algorithm's structure.
Visitor (331) Represent an operation to be performed on the elements of an object
structure. Visitor lets you define a new operation without changing the classes of
the elements on which it operates.
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Design Patterns
Elements of Reusable Object-Oriented Software
Erich Gamma
Richard Helm
Ralph Johnson
John Vlissides
Boston • San Francisco • New York • Toronto • Montreal
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Material from A Pattern Language: Towns/Buildings/Construction by Christopher Alexander,
copyright © 1977 by Christopher Alexander is reprinted by permission of Oxford University
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Library of Congress Cataloging-in-Publication Data
Design Patterns : elements of reusable object-oriented software / Erich Gamma ... [et al.].
p. cm.—(Addison-Wesley professional computing series)
Includes bibliographical references and index.
ISBN 0-201-63361-2
1. Object-oriented programming (Computer science) 2. Computer software—Reusability.
I. Gamma, Erich. II. Series.
QA76.64.D47 1994
005.1'2-dc20 94-34264
CIP
Copyright © 1995 by Addison-Wesley
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or
transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording, or other-
wise, without the prior consent of the publisher. Printed in the United States of America. Published
simultaneously in Canada.
Cover art © M.C. Escher/Cordon Art - Baarn - Holland. All rights reserved.
ISBN 0-201-63361-2
Text printed in the United States on recycled paper at Courier Westford in Westford, Massachusetts.
37th Printing March 2009
To Karin
—E.G.
To Sylvie
—R.H.
To Faith
-R.J.
To Dru Ann and Matthew
Joshua 24:15b
—J.v.
Praise for Design Patterns: Elements of Reusable
Object-Oriented Software
"This is one of the best written and wonderfully insightful books that I have read in a great long while...this
book establishes the legitimacy of patterns in the best way: not by argument but by example."
— Stan Lippman, C++ Report
"...this new book by Gamma, Helm, Johnson, and Vlissides promises to have an important and lasting
impact on the discipline of software design. Because Design Patterns bills itself as being concerned with
object-oriented software alone, I fear that software developers outside the object community may ignore it.
This would be a shame. This book has something 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 it."
— Tom DeMarco, IEEE Software
"Overall, I think this book represents 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. This book is
certainly one that I shall turn to often in search of powerful object-oriented design ideas; after all, that's
what reuse is all about, isn't it?"
— Sanjiv Gossain, Journal of Object-Oriented Programming
"This much-anticipated book lives up to its full year of advance buzz. The metaphor is of an architect's
pattern book filled with time-tested, usable designs. The authors have chosen 23 patterns from decades of
object-oriented experience. The brilliance of the book lies in the discipline represented by that number.
Give a copy of Design Patterns to every good programmer you know who wants to be better."
— Larry O'Brien, Software Development
"The simple fact of the matter is that patterns have the potential to permanently alter the software
engineering field, catapulting it into the realm of true elegant design. Of the books to date on this subject,
Design Patterns is far and away the best. It is a book to be read, studied, internalized, and loved. The book
will forever change the way you view software."
— Steve Bilow, Journal of Object-Oriented Programming
"Design Patterns is a powerful book. After a modest investment of time with it, most C++ programmers
will be able to start applying its "patterns" to produce better software. This book delivers intellectual
leverage: concrete tools that help us think and express ourselves more effectively. It may fundamentally
change the way you think about programming.
— Tom Cargill, C++ Report