Patterns in Java, Volume 1—A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition by Mark Grand John Wiley & Sons © 2002 Patterns in Java, Volume 1—A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition Mark Grand Wiley Publishing Company 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 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 percopy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4744 Requests to the Publisher for permission should be addressed to the Legal Department, Wiley Publishing, Inc., 10475 Crosspointe Blvd., Indianapolis, IN 46256, (317) 572-3447, fax (317) 572-4447, E-mail: permcoordinator@wiley.com This publication is designed to provide accurate and authoritative information in regard to the subject matter covered It is sold with the understanding that the publisher is not engaged in professional services If professional advice or other expert assistance is required, the services of a competent professional person should be sought Library of Congress Cataloging-in-Publication Data: ISBN: 0-471-22729-3 Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic versions For more information about Wiley products, visit our web site at www.wiley.com Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 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 corrections 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 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 convinced me of the importance of patterns Craig also provided me with much invaluable feedback on the use of UML and the presentation of patterns 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 About the Author Mark Grand is an Atlanta-based consultant with over 23 years of experience specializing in distributed systems, object-oriented design, and Java He was the architect for the first commercial business-tobusiness (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 software architect, database architect, network designer and administrator, and Sun System administrator He has been involved with object-oriented programming and design since 1982 Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition ISBN:0471227293 by Mark Grand John Wiley & Sons 2002 (580 pages) In-depth coverage of forty-seven Java design patterns Table of Contents Back Cover Table of Contents Patterns in Java, Volume 1—A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition Chapter 1 - Introduction to Software Patterns Chapter 2 - Overview of UML Chapter 3 - The Software Life Cycle Chapter 4 - Fundamental Design Patterns Chapter 5 - Creational Patterns Chapter 6 - Partitioning Patterns Chapter 7 - Structural Patterns Chapter 8 - Behavioral Patterns Chapter 9 - Concurrency Patterns Overview of Patterns in Java, Volumes 1 Appendix through 3 Bibliography Index List of Figures List of Tables List of Sidebars Chapter 1 - Introduction to Software Patterns Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition by Mark Grand John Wiley & Sons © 2002 Chapter 1: Introduction to Software Patterns List of Tables Chapter 2: Overview of UML Table 2.1: Visibility Indicators Chapter 7: Structural Patterns Table 7.1: Cache Size and Hit Rates Chapter 8: Behavioral Patterns Table 8.1: Word Combination Language Table 8.2: Lexical Rules for the Word Combination Language Table 8.3: Comparison of State Saving by Serialization and Memento Objects List of Sidebars Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition by Mark Grand John Wiley & Sons © 2002 List of Sidebars Chapter 4: Fundamental Design Patterns Doubly Linked List Clone() Chapter 7: Structural Patterns Inner Classes Chapter 8: Behavioral Patterns Delegation Event Model Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition by Mark ISBN:0471227293 Grand John Wiley & Sons © 2002 (580 pages) In-depth coverage of forty-seven Java design patterns Table of Contents Back Cover Back Cover Since the publication of the first edition in 1998, programmers and developers have been waiting eagerly for an update to this expert guide on how to use Java in conjunction with the timesaving design patterns that have surfaced in the past few years With the new edition of his bestselling Patterns in Java, Volume 1, Mark Grand brings you up to date with the latest release of Java and many of the important concerns facing Java programmers today If you are a programmer or developer who wants to take advantage of new patterns, but doesn’t have the time or experience to document them for your organization, this book is for you As with the first edition, each pattern is documented in UML and, where appropriate, a code example or an example in the core Java API is provided This comprehensive book gives you: Seven fundamental design patterns Six creational patterns Three partitioning patterns Nine structural patterns Eleven behavioral patterns Eleven concurrency patterns UML documentation of all 47 patterns Practical, hands-on examples of pattern implementation in Java About the Author Mark Grand is an Atlanta-based consultant with over twenty-three years of experience in distributed systems, object-oriented design, and Java He is currently working on an open source framework fro gluing components and programs into an application He is also the author of Patterns in Java, Volume 2, and Java Enterprise Design Patterns (both from Wiley) Chapter 2 - Overview of UML Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition by Mark Grand John Wiley & Sons © 2002 Chapter 2: Overview of UML Overview The Unified Modeling Language (UML) is a notation that you can use for object-oriented analysis and design This chapter contains a brief overview of UML that introduces you to the subset of UML and the extensions to UML used in this book For a complete description of UML, see www.omg.org/technology/documents/formal/uml.htm Books that are specifically about UML call the pieces of information stored in instances of a class attributes; they call a class’s encapsulations of behavior operations Those terms, as with UML, are not specific to any implementation language This book is not language neutral; it assumes that you use Java as your implementation language It also uses Java- specific terms in most places rather than terms that are language neutral but less familiar to Java programmers For example, it uses the words attribute and variable interchangeably, with preference for the Java-specific term variable This book also uses the words operation and method interchangeably, with preference for the Java-specific term method UML defines a number of different kinds of diagrams The rest of this chapter is organized into sections that describe different kinds of UML diagrams and the elements that appear in them If you are experienced with object-oriented design, you will find most of the concepts underlying the UML notation to be familiar If you find many concepts unfamiliar, read only as much of this chapter as you feel comfortable with When you see a UML diagram in later chapters that contains something that you want explained, come back to this chapter and find a diagram that contains the UML element that you want explained ... The Java examples that appear in this book are based on Java version 1. 4 Chapter 2 - Overview of UML Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition by Mark Grand... Related Patterns This section contains a list of patterns that are related to the pattern described Chapter 1 - Introduction to Software Patterns Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with. .. administrator, and Sun System administrator He has been involved with object-oriented programming and design since 19 82 Patterns in Java, Volume 1: A Catalog of Reusable Design Patterns Illustrated with UML, Second Edition ISBN: 04 712 27293