Abstract

The documentation is missing or obsolete, and the original developers have departed. Your team has limited understanding of the system, and unit tests are missing for many, if not all, of the components. When you fix a bug in one place, another bug pops up somewhere else in the system. Long rebuild times make any change difficult. All of these are signs of software that is close to the breaking point.
Many systems can be upgraded or simply thrown away if they no longer serve their purpose. Legacy software, however, is crucial for operations and needs to be continually available and upgraded. How can you reduce the complexity of a legacy system sufficiently so that it can continue to be used and adapted at acceptable cost?
Based on the authors' industrial experiences, this book is a guide on how to reverse engineer legacy systems to understand their problems, and then reengineer those systems to meet new demands. Patterns are used to clarify and explain the process of understanding large code bases, hence transforming them to meet new requirements. The key insight is that the right design and organization of your system is not something that can be evident from the initial requirements alone, but rather as a consequence of understanding how these requirements evolve.
* Describes how to reverse engineer a monolithic system to understand how it really works and how to identify potential problems.
* Includes reengineering patterns that tackle well-known reengineering techniques often encountered in object-oriented programming, such as introducing polymorphism, factoring out common behavior, detecting duplicated code, and understanding design.
* Shows how to build a culture of continuous reengineering for achieving flexible and maintainable object-oriented systems.
"'How' to refactor is already well covered in the literature. However, 'When' and 'Why' can only be learned by experience. This book will give you a head start in learning when to start redesigning a system, when to stop for now, and what effects you can expect to see from your efforts."
—Kent Beck, Director, Three Rivers Institute
"This book full of practical, hands-on reengineering knowledge and expertise presented in a form that makes it easy to understand and use. The patterns in this book thus help everyone who is concerned with reengineering to guide their work. I wished I had had this book in my library earlier."
—Frank Buschmann, Senior Principal Engineer, Siemens AG
"This book is more than its title advertises. Effective reengineering is really about purposeful and efficient reading of someone else's code in order to produce predictable change. The same processes the authors highlight as patterns of skillful reengineering behavior can easily be cast as the skills you need to create readable, maintainable software systems."
—Adele Goldberg, Neometron, Inc.
"If a guy named Dave brought a large box to my office that contained a lot of documentation and two CDs—installation disks for software that my company wanted to reengineer—I'd be happy to have the authors of this book at my side. Barring that, having their book is the next best thing. No silver bullets, no hype, no promises that this will be easy—just a down-to-earth, easy-to-read, extremely useful book of helpful guidelines to tackle the project. Buy this book and browse it before Dave arrives in your office! It just might save you and your company a lot of grief."
—Linda Rising, Independent Consultant