But Bob, you said you’d be done with the book last year.
—Claudia Frers, UML World, 1999
It’s been seven years since Claudia’s justifiable complaint, but I think I have made up for it. Publishing three books—one book every other year while running a consulting company and doing a lot of coding, training, mentoring, speaking, and writing articles, columns, and blogs—not to mention raising a family and enjoying a grandfamily can be quite a challenge. But I love it.
Agile development is the ability to develop software quickly, in the face of rapidly changing requirements. In order to achieve this agility, we need to use practices that provide the necessary discipline and feedback. We need to employ design principles that keep our software flexible and maintainable, and we need to know the design patterns that have been shown to balance those principles for specific problems. This book is an attempt to knit all three of these concepts together into a functioning whole.
This book describes those principles, patterns, and practices and then demonstrates how they are applied by walking through dozens of different case studies. More important, the case studies are not presented as complete works. Rather, they are designs in progress. You will see the designers make mistakes and observe how they identify them as mistakes and eventually correct them. You will see the designers puzzle over conundrums and worry over ambiguities and trade-offs. You will see the act of design.
In early 2005, I was on a small development team that began work on a .NET application to be written in C#. Using agile development practices was mandatory, which is one of the reasons I was involved. Although I had used C# before, most of my programming experience was in Java and C++. I didn’t think that working in .NET would make much difference; in the end it didn’t.
Two months into the project, we made our first release. It was a partial release containing only a fraction of all the intended features, but it was enough to be usable. And use it they did. After only two months, the organization was reaping the benefits of our development. Management was so thrilled that it asked to hire more people so we could start more projects.
Having participated in the agile community for years, I knew a good many agile developers who could help us. I called them all and asked them to join us. Not one of my agile colleagues ended up joining our team. Why not? Perhaps the most overwhelming reason was the fact that we were developing in .NET.
Almost all agile developers have a background in Java, C++, or Smalltalk. But agile .NET programmers are almost unheard of. Perhaps my friends didn’t take me seriously when I said we were doing agile software development with .NET, or maybe they were avoiding association with .NET. This was a significant problem. It was not the first evidence I’d seen of this problem, either.
Teaching week-long courses on various software topics allows me to meet a wide cross-section of developers from around the world. Many of the students I’ve instructed were .NET programmers, and many were Java or C++ programmers. There’s no gentle way to put this: In my experience, .NET programmers are often weaker than Java and C++ programmers. Obviously, this is not always the case. However, after observing it over and over in my classes, I can come to no other conclusion: .NET programmers tend to be weaker in agile software practices, design patterns, design principles, and so on. Often in my classes, the .NET programmers had never heard of these fundamental concepts. This has to change.
The first edition of this book, Agile Software Development: Principles, Patterns, and Practices, by Robert C. Martin, my father, was published in late 2002 and won the 2003 Jolt Award. It is a great book, celebrated by many developers. Unfortunately, it had little impact on the .NET community. Despite the fact that the content of the book is equally relevant to .NET, few .NET programmers have read it.
It is my hope that this .NET edition acts as a bridge between .NET and the rest of the developer community. I hope that programmers will read it and see that there are better ways to build software. I hope that they will begin using better software practices, creating better designs, and raising the bar for quality in .NET applications. I hope that .NET programmers will not be weaker than other programmers. I hope that .NET programmers achieve a new status in the software community such that Java developers are proud to join a .NET team.
Throughout the process of putting this book together, I struggled many times with the concept of my name being on the cover of a .NET book. I questioned whether I wanted my name associated with .NET and all the negative connotations that seemed to come with it. Yet I can no longer deny it. I am a .NET programmer. No! An agile .NET programmer. And I’m proud of it.
About This Book
A Little History
In the early 1990s I (Bob) wrote Designing Object-Oriented C++ Applications Using the Booch Method. That book was something of a magnum opus for me, and I was very pleased with the result and the sales.
The book you are reading started out as a second edition to Designing, but that’s not how it turned out. Very little remains of the original book in these pages. Little more than three chapters have been carried through, and those have been massively changed. The intent, spirit, and many of the lessons of the book are the same. In the decade since Designing came out, I’ve learned a tremendous amount about software design and development. This book reflects that learning.
What a decade! Designing came out just before the Internet collided with the planet. Since then, the number of acronyms we have to deal with has doubled. We have EJB, RMI, J2EE, XML, XSLT, HTML, ASP, JSP, ZOPE, SOAP, C#, and .NET, as well as Design Patterns, Java, Servelets, and Application Servers. Let me tell you, it’s been difficult to keep the chapters of this book current.
The Booch connection In 1997, I was approached by Grady Booch to help write the third edition of his amazingly successful Object-Oriented Analysis and Design with Applications. I had worked with Grady before on some projects and had been an avid reader and contributor to his various works, including UML. So I accepted with glee and asked my good friend Jim Newkirk to help out with the project.
Over the next two years, Jim and I wrote a number of chapters for the Booch book. Of course, that effort meant that I could not put as much effort into this book as I would have liked, but I felt that the Booch book was worth contributing to. Besides, at the time, this book was simply a second edition of Designing, and my heart wasn’t in it. If I was going to say something, I wanted to say something new and different.
Unfortunately, the Booch book was not to be. It is difficult to find the time to write a book during normal times. During the heady days of the dot-com bubble, it was nearly impossible. Grady got ever busier with Rational and with new ventures such as Catapulse. So the project stalled. Eventually, I asked Grady and Addison-Wesley whether I could have the chapters that Jim and I wrote to include in this book. They graciously agreed. So several of the case study and UML chapters came from that source.
The impact of Extreme Programming In late 1998, XP reared its head and challenged our cherished beliefs about software development. Should we create lots of UML diagrams prior to writing any code? Or should we eschew any kind of diagrams and simply write lots of code? Should we write lots of narrative documents that describe our design? Or should we try to make the code narrative and expressive so that ancillary documents aren’t necessary? Should we program in pairs? Should we write tests before we write production code? What should we do?
This revolution came at an opportune time. During the middle to late 1990s, Object Mentor was helping quite a few companies with OO design and project management issues. We were helping companies get their projects done. As part of that help, we instilled into the teams our own attitudes and practices. Unfortunately, these attitudes and practices were not written down. Rather, they were an oral tradition that was passed from us to our customers.
By 1998, I realized that we needed to write down our process and practices so that we could better articulate them to our customers. So I wrote many articles about process in the C++ Report. 1 These articles missed the mark. They were informative and in some cases entertaining, but instead of codifying the practices and attitudes that we used in our projects, they were an unwitting compromise to values that had been imposed on me for decades. It took Kent Beck to show me that.
The Beck connection In late 1998, at the same time I was fretting over codifying the Object Mentor process, I ran into Kent’s work on Extreme Programming (XP). The work was scattered through Ward Cunningham’s wiki 2 and was mixed with the writings of many others. Still, with some work and diligence, I was able to get the gist of what Kent was talking about. I was intrigued but skeptical. Some of the things that XP talked about were exactly on target for my concept of a development process. Other things, however, such as the lack of an articulated design step, left me puzzled.
Kent and I could not have come from more disparate software circumstances. He was a recognized Smalltalk consultant, and I was a recognized C++ consultant. Those two worlds found it difficult to communicate with each other. There was an almost Kuhnian3 paradigm gulf be...