9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page iii Patterns in Java™, Volume 1 A Catalog of Reusable Design Patterns Illustrated with UML Second Edition MARK GRAND Wiley Publishing, Inc. 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page ii 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page i Patterns in Java™, Volume 1 Second Edition 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page ii 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page iii Patterns in Java™, Volume 1 A Catalog of Reusable Design Patterns Illustrated with UML Second Edition MARK GRAND Wiley Publishing, Inc. 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page iv Publisher: Robert Ipsen Editor: Theresa Hudson Developmental Editor: Kathryn Malin Managing Editor: Angela Smith New Media Editor: Brian Snapp Text Design & Composition: North Market Street Graphics Designations used by companies to distinguish their products are often claimed as trademarks. In all instances where Wiley Publishing, Inc. is aware of a claim, the product names appear in initial capital or all capital letters. Readers, however, should contact the appropriate companies for more complete information regarding trademarks and registration. This book is printed on acid-free paper. ●∞ Copyright © 2002 by Mark Grand. All rights reserved. Published by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada. 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, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4744. 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Printed in the United States of America. 10 9 8 7 6 5 4 3 2 1 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page v CONTENTS Acknowledgments ix About the Author xi Chapter 1 Introduction to Software Patterns 1 Patterns Description 2 A Brief History of Patterns 4 Organization of This Book 5 Chapter 2 Overview of UML 7 Class Diagram 8 Collaboration Diagram 18 Statechart Diagram 27 Deployment Diagram 29 vvv 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page vi vi ■ Contents Chapter 3 The Software Life Cycle 31 Case Study 34 Business Case 34 Define Requirements Specification 35 Develop High-Level Essential Use Cases 37 Object-Oriented Analysis 39 Object-Oriented Design 40 Chapter 4 Fundamental Design Patterns 51 Delegation (When Not to Use Inheritance) 53 Interface 61 Abstract Superclass 67 Interface and Abstract Class 73 Immutable 79 Marker Interface 85 Proxy 91 Chapter 5 Creational Patterns 101 Factory Method 103 Abstract Factory 119 Builder 129 Prototype 139 Singleton 149 Object Pool 159 Chapter 6 Partitioning Patterns 175 Filter 177 Composite 187 Read-Only Interface 199 Chapter 7 Structural Patterns 207 Adapter 209 Iterator 217 Bridge 223 Façade 235 Flyweight 243 Dynamic Linkage 255 Virtual Proxy 265 Decorator 275 Cache Management 283 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page vii Contents ■ vii Chapter 8 Behavioral Patterns 303 Chain of Responsibility 305 Command 317 Little Language 329 Mediator 355 Snapshot 369 Observer 387 State 397 Null Object 407 Strategy 413 Template Method 419 Visitor 427 Chapter 9 Concurrency Patterns 439 Single Threaded Execution 443 Lock Object 453 Guarded Suspension 461 Balking 469 Scheduler 475 Read/Write Lock 485 Producer-Consumer 495 Two-Phase Termination 501 Double Buffering 507 Asynchronous Processing 523 Future 535 Appendix Overview of Patterns in Java, Volumes 1 through 3 547 Bibliography 567 Index 569 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page viii 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page ix ACKNOWLEDGMENTS I would first like to acknowledge the patience of my wife, Nicole. Without her support, this second edition of Patterns in Java, Volume 1 would not have been possible. I would also like to acknowledge the feedback that I have received from many readers whose emails to me suggested improvements and cor- rections that have gone into this second edition. I would like to single out Ed Remmell, who organized a discussion group around my book and took the time to send me summaries of the discussions. Other readers who took the time and trouble to send me useful questions and comments are (in alphabetical order): Nader Afshar, Derrick Ampy, Barry W. Anderson, Paul E. Andrighetti, Kaushik Barot, Ted Beckett, Pablo Bellver, Davide De Benedictis, Dave Busse, Mike Carlin, Max Chandler, John Clarke, Charlie Crook, Christian Cryder, Carlos Devoto, Cyrus Doomasia, Rodrigo Figueiredo, Jeff French, Brent Fry, Srinivas Ganti, Daniel L. Gleneck, Satish Gupta, Barton W. Hammond, Shannon Harvey, Judy Housman, Hong Hsu, Rob Hulsebos, Gary Janes, Brian Krahmer, Erik Bak Kristensen, Robert Laganière, Laurene O. Laidlaw, Allen Lee, Roger Lee, Tim Lethbridge, Charles Magid, Kurt Matthys, Phil McGlauchlin, Barry ixixix 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page x x ■ Acknowledgments Middlebrook, Sadiq Mohammed, Thomas Moore, Raymond Naseef, Jaime Nino, Jeff Oakes, Sudesh Palekar, Greg Pearman, Jim Phipps, John Pinto, Jon Poploskie, Raj Prathinidhi, Andy Pryke, Tulsi Rai, Damith C. Rajapakse, Steven Ranieri, John Sargeant, Robert Allan Schwartz, Greg Scott, Joe Sharp, Mike Shivas, Eduardo Silva, Daniel Stainhauser, Steve Stephens, Christian Svenstrup, Oyvind Teig, Alan Thompson, Richard Tomlinson, Bruce Wallace, Dieter Wankmueller, Mark Waschkowski, Richard Williams, Joe Wissmann, Robert Wragg, Wayne Wylupski, and Hong Yan. Acknowledgments from the First Edition I want to thank Craig Larman, my most conscientious reviewer. He con- vinced me of the importance of patterns. Craig also provided me with much invaluable feedback on the use of UML and the presentation of pat- terns. His valuable suggestions greatly improved the way that I present the patterns in this book. Jack Harich was another manuscript reviewer who made many useful suggestions about the organization of this book. He convinced me to expand my coverage of fundamental patterns. He also supplied the example that I use for the State pattern. Brad Appleton provided me with the most voluminous and detailed comments. The UIUC patterns group provided some insightful discussions for the patterns in this book. The participants in those discussions included Brian Foote, Ed Peters, Dragos Malonescu, Peter Hatch, Don Roberts, Joseph W. Yoder, Ralph Johnson, John Brant, James Overturf, Jean Pierre Briot, Eiji Nabika, Hiro Nakamura, and Ian Chai. I also want to acknowledge some of my other reviewers, in particular Micheal Wheaton and Micheal Pair. 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page xi ABOUT THE AUTHOR Mark Grand is an Atlanta-based consultant with over 23 years of experi- ence specializing in distributed systems, object-oriented design, and Java. He was the architect for the first commercial business-to-business (B2B) e-commerce product for the Internet. He is currently working on an open source framework for gluing components and programs into an application. Mark Grand is most widely known for his best-selling Patterns in Java books. In addition to teaching Java for Sun and other training organizations, Mark has been involved in several large-scale commercial Java projects. Prior to his involvement with Java, Mark spent over 11 years as a designer and implementer of fourth-generation languages (4GLs). His most recent role in that vein was as the architect and project manager for an electronic data interchange product. Mark has worked with a number of information technology (IT) organizations in capacities such as soft- ware architect, database architect, network designer and administrator, and Sun System administrator. He has been involved with object-oriented programming and design since 1982. 9525_Grand_fm_v.qxd 8/26/02 9:23 AM Page xii 9525_Grand_01_v.qxd 8/26/02 9:07 AM Page 1 1 CHAPTER Introduction to Software Patterns Software patterns are reusable solutions to recurring problems that we encounter during software development. Because this book is all about software patterns, they are simply referred to as patterns throughout. What makes a bright, experienced programmer much more produc- tive than a bright, but inexperienced programmer? Experience. Experience gives programmers a wealth of wisdom. As programmers gain experience, they recognize the similarity of new problems to those they have solved in the past. With even more experience, they recognize that solutions to simi- lar problems follow recurring patterns. With knowledge of these patterns, experienced programmers can recognize a problem to which specific pat- terns apply and immediately determine the solution without having to stop to analyze the problem first. When a programmer discovers a pattern, it’s just an insight. In most cases, to go from an unverbalized insight to a well-thought-out idea that the programmer can clearly articulate is surprisingly difficult. It’s also an extremely valuable step. When we understand a pattern well enough to put it into words, we are able to intelligently combine it with other patterns.