This book discusses the implementation of medium- sized software systems in an object oriented way. It turns concepts and principles underlying the object oriented paradigm into concrete coding advices and coding rules. It further illustrates how to apply each of them in the popular programming language Java. Throughout the book, software quality is the main driving force. At regular times, the author intensively discusses how decisions influence conflicting quality criteria such as adaptability and efficiency.The first part of the book focuses on the specification and the implementation of a single class. The object oriented paradigm suggests to structure software systems as clusters of classes whose objects interact with each other. The second part of the book demonstrates how to implement unidirectional and bidirectional associations between objects in terms of references. In the third and final part of the book the notion of inheritance as the driving force to develop hierarchies of classes is discussed.ERIC STEEGMANS is professor at the Department of Computer Science of the K.U.Leuven. He teaches courses on object oriented programming,on programming languages and on requirements analysis in the bachelor-master programs on informatics/computer science.