Annotation Capturing the wealth of experience about the design of object-oriented software, these four top-notch authors show how object-oriented systems exhibit recurring patterns and structures of objects that solve particular design problems, allowing designers to reuse successful designs and architectures without having to rediscover the design solutions. Central to this book is a catalog of 23 design patterns that have seen successful practical application and are representative of good object-oriented design. Each pattern describes the circumstances in which it is applicable, when it can be applied in view of other design constraints, and the consequences and tradeoffs of using the pattern in a larger design. Finally, every pattern includes code that shows how it may be implemented in object-oriented programming languages like C++ and Smalltalk.