Capturing a wealth of experience about the design of object-oriented software, four top-notch designers present a catalog of simple and succinct solutions to commonly occurring design problems. Previously undocumented, these 23 patterns allow designers to create more flexible, elegant, and ultimately reusable designs without having to rediscover the design solutions themselves.
　　The authors begin by describing what patterns are and how they can help you design object-oriented software. They then go on to systematically name, explain, evaluate, and catalog recurring designs in object-oriented systems. With Design Patterns: Elements of Reusable Object-Oriented Software as your guide, you will learn how these important patterns fit into the software development process, and how you can leverage them to solve your own design problems most efficiently.
　　Each pattern describes the circumstances in which it is applicable, when it can be applied in view of other design constraints, and the consequences and trade-offs of using the pattern within a larger design. AII patterns are compiled from real systems and are based on real-world examples. Each pattern also includes code that demonstrates how it may be implemented in object-oriented programming languages like C++ or Smalltalk.

This book isn't an introduction to object-oriented technology or design. Many books already do a good job of that. This book assumes you are reasonably proficient in at least one object-oriented programming language, and you should have some experience in object-oriented design as well. You definitely shouldn't have to rush to the nearest dictionary the moment we mention "types" and "polymorphism," or "interface" as opposed to "implementation" inheritance.
　　On the other hand. this isn't an advanced tecltnical treatise either. It's a book of design patterns that describes simple and elegant solutions to specific problems in objectoriented software design. Design patterns capture solutions that have developed and evolved over time. Hence they aren't the designs people tend to generate initially. They reflect untold redesign and recoding as developers have struggled for greater reuse and flexibility in their software. Design patterns capture these solutions in a succinct and easily applied form.
　　The design patterns requite neither unusual language features nor amazing programming tricks with which to astound your friends and managers. An can be implemented in standard object-oriented languages, though they might take a little more work than ad hoc solutions. But the extra effort invariably pays dividends in increased flexibility and reusability.
　　Once you understand the design patterns and have had an "Aha!" (and not just a "Huh ") experience with them, you won't ever think about object-oriented design in the same way. You'll have insights that can make your own designs more flexible, modular, reusable, and understandable---which is why you're interested in objectoriented technology in the first place, right
　　A word of warning and encouragement: Don't worry if you don't understand this book completely on the fint reading. We didn't understand it all on the first writing!Remember that this isn't a book to read once and put on a shelf. We hope you'll find yourself referring to it again and again for design insights and for inspiration.
　　This book has had a long gestation. It has seen four countries, three of its authors' marriages, and the birth of two (unrelated) offspring. Many people have had a part in its development. Special thanks are due Bruce Anderson, Kent Beck, and Andre Weinand for their inspiration and advice. We also thank those who reviewed drafts of the manuscript: Roger Bielefeld, Grady Booch, Tom Cargill, Marshall Cline, Ralph Hyre, Brian Kernighan, Thomas Laliberty, Mark Lorenz, Arthur Riel, Doug Schmidt,Clovis Tondo, Steve Vinoski, and Rebecca Wirfs-Brock. We are also grateful to the team at Addison-Wesley for their help and patience: Kate Habib, Tiffany Moore, Lisa Raffaele, Pradeepa Siva, and John Wait. Special thanks to Carl Kessler, Danny Sabbah,and Mark Wegman at IBM Research for their unflagging support of this work.
　　Last but certainly not least, we thank everyone on the Internet and points beyond who commented on versions of the patterns, offered encouraging words, and told us that what we were doing was woratwhile. These people include but are not limited to Jon Avotins, Steve Berczuk, Julian Berdych, Matthias Bohlen, John Brant, Allan Clarke,Paul Chisholm, Jens Coldewey, Dave Collins, Jim Coplien, Don Dwiggins, Cabriele Elia,Doug Felt, Brian Foote, Denis Fortin, Ward Harold, Hermann Hueni, Nayeem Islam,Bikramjit Kalra, Paul Keefer, Thomas Kofler, Doug Lea, Dan LaLiberte, James Long,Ann Louise Luu, Pundi Madhavan, Brian Marick, Robert Martin, Dave McComb, Carl McConnell, Christine Mingins. Hanspeter Mossenbock, Eric Newton, Marianne Ozkan,Roxsan Payette, Larry Podmolik, George Radin, Sita Ramakrishnan, Russ Ramirez,Alexander Ran, Dirk Riehle, Bryan Rosenburg. Aamod Sane, Duri Schmidt, Robert Seidl, Xin Shu, and Bill Walker.
We don't consider this collection of design patterns complete and static; it's more a recording of our current thoughts on design. We welcome comments on it, whether criticisms of our examples, references and known uses we've missed, or design patterns we should have included. You can write us care of Addison-Wesley, or send electronic mail to design-patterns@cs . uiuc . edu. You can also obtain softcopy for the code in the Sample Code sections by sending the message "send design patternsource" to design-patterns-source@cs . uiuc . edu And now there's a Web page at http : / /st-www. cs .uiuc . edu/ussrs/patterns/DPBook/DPBook. html for late-breaking information and updates.

Mountain View, California E.G.
Montreal, Quebec R.H.
Urbana, Illinois R.J
Hawthorne, New York J.V.
4ugusf 1994 '

Erich Gamma,Richard Helm,Ralph Johnson,John Vlissides：Erich Gamma: 在苏黎世大学获得计算机科学博士学位，曾供职于瑞士联邦银行、Taligent、OTI公司。现在是Eclipse项目的主要技术负责人之一。
Richard Helm: 在墨尔本大学获得计算机科学博士学位，曾在IBM T.J. Watson 担任研究员。现在IBM咨询集团供职。
Ralph Johnson: 在康内尔大学获得计算机科学博士学位，目前是伊利诺伊大学教授，在模式、重构等领域均有很高造诣。
John Vlissides: 在斯坦福大学获得计算机科学博士学位，目前是 IBM T.J. Watson 研究中心的研究员。除本书外，他还是 Addison-Wesley “软件模式”丛书的顾问。

Preface
Foreword
Guide to Readers
1 Introduction
1.1 What Is a Design Pattern
1.2 Design Patterns in Smalltalk MVC
1.3 Describing Design Patterns
l.4 The Catalog of Design Patterns
1.5 Organizing the Catalog
1.6 How Design Patterns Solve Design Problems
1.7 How to Select a Design Pattern
1.8 How to Use a Design Pattern
2 A Case Study: Designing a Document Editor
2.1 Design Problems
2.2 Document Structure
2.3 Formatting
2.4 Embellishing the User Interface
2.5 Supporting Multiple Look-and-Feel Standards
2.6 Supporting Multiple Window Systems
2.7 User Operations
2.8 Spelling Checking and Hyphenation
2.9 Summary
Design Pattern Catalog
3 Creational Patterns
Abstract Factory
Builder
Factory Method
Prototype
Singleton
Discussion of Creational Patterns
4 Structural Patterns
Adapter
Bridge
Composite
Decorator
Facade
Flyweight
Proxy
Discussion of Structural Patterns
5 Behavioral Patterns
Chain of Responsibility
Command
Interpreter
Iterator
Mediator
Memento
Observer
State
Strategy
Template Method
Visitor
Discussion of Behavioral Patterns
6 Conclusion
6.1 What to Expect from Design Patterns
6.2 A Brief History
6.3 The Pattern Community
6.4 An Invitation
6.5 A Parting Thought
A Glossary
B Guide to Notation
B.1 Class Diagram
8.2 Object Diagram
B.3 Interaction Diagram
C Foundation Classes
C.l List
C.2 Iterator
C.3 ListIterator
C.4 Point
C.5 Red
Bibliography
Index