At OOPSLA 2000 in Minneapolis, Minnesota, I asked Mike Hendrickson of Addison-Wesley what types of books he thought readers wanted. I was interested to hear that he felt that there is still a market for books to help readers understand design patterns. I suggested the idea of a Java workbook that would give readers a chance to expand and to exercise their understanding of patterns. This sounded good to Mike, and he introduced me to Paul Becker, who supports Addison-Wesley's Software Patterns series. Paul's immediate response was that such a book "should have been written five years ago." I would like to thank Mike and Paul for their initial encouragement, which inspired me to take on this task. Since that initial meeting, Paul has supported me throughout the entire development process, guiding this book toward publication. Early on, Paul asked John Vlissides, the Software Patterns series editor, for his views on the project. John's reply was that Paul should support the project "in all wise," inspirational words that have stayed with me throughout. John Vlissides is also, of course, one of the four authors of Design Patterns . John and his coauthors--Erich Gamma, Ralph Johnson, and Richard Helm--produced the work that is in every way the foundation of this book. I referred to Design Patterns nearly every day that I worked on this book and can hardly overstate my reliance on it. I have also relied on many other existing books, which are listed in the bibliography at the end of this book. In particular, I have depended on The Unified Modeling Language User Guide (Booch, Rumbaugh, and Jacobson 1999) for its clear explanations of UML. For accuracy in Java-related topics I have consulted Java in a Nutshell (Flanagan 1999b) almost daily. I have also repeatedly drawn on the insights in Patterns in Java (Grand 1998) and Java Design Patterns (Cooper 2000). During the months that I was working on this book, I also worked at a financial services institution that has facilities in many locations. As the book emerged, I developed an instructor's course to go with it. I taught the course in Richmond, Virginia, and my associates Tim Snyder and Bill Trudell taught the course concurrently at other locations. I would like to thank these instructors and the students from all three courses for their inspiration and their many insights. In particular, I would like to thank Srinivasarao Katepalli, Brad Hughes, Thiaga Manian, Randy Fields, Macon Pegram, Joe Paulchell, Ron DiFrango, Ritch Linklater, Patti Richards, and Ben Lewis for their help and suggestions. I would also like to thank my friends Bill Wake and Gagan Kanjlia for their reviews of this book in its early stages and Kiran Raghunathan for his help in the later stages. Finally, I'd like to thank my friend Jeff Damukaitis for his suggestions, particularly his insistence that I make the code for this book available to readers. (It is, at [a href="http://www.oozinoz.com" target="new">oozinoz.com ). As the book came along, Paul Becker arranged for many excellent reviewers to help guide its progress. I'd like to thank John Vlissides again for his reviews. In every review, John somehow convinced me that he liked the book while simultaneously pointing out scores of significant improvements. I'd like to thank Luke Hohmann, Bob Hanmer, Robert Martin, and Joshua Kerievsky for their help at various stages. Each of them made this book better. I'd like to thank Joshua Engel, who has an amazing ability to blend sharp insight with a gentle touch. Finally, I'd like to thank Rebecca Wirfs-Brock, who had many great suggestions, including completely reorganizing the book. I had initially not taken care to put important but understandable patterns up front. The book is much stronger now because of Rebecca's advice and the help of all the book's reviewers. Steve Metsker (Steve.Metsker@acm.org ) 0201743973P03262002