This book was motivated by my experience in teaching the course E&CE 250: Algorithms and Data Structures in the Computer Engineering program at the University of Waterloo. I have observed that the advent of object-oriented methods and the emergence of object-oriented design patterns has lead to a profound change in the pedagogy of data structures and algorithms. The successful application of these techniques gives rise to a kind of cognitive unification: Ideas that are disparate and apparently unrelated seem to come together when the appropriate design patterns and abstractions are used.

This paradigm shift is both evolutionary and revolutionary. On the one hand, the knowledge base grows incrementally as programmers and researchers invent new algorithms and data structures. On the other hand, the proper use of object-oriented techniques requires a fundamental change in the way the programs are designed and implemented. Programmers who are well schooled in the procedural ways often find the leap to objects to be a difficult one.

The primary goal of this book is to promote object-oriented design using Java and to illustrate the use of the emerging object-oriented design patterns. Experienced object-oriented programmers find that certain ways of doing things work best and that these ways occur over and over again. The book shows how these patterns are used to create good software designs. In particular, the following design patterns are used throughout the text: singleton, container, enumeration, adapter and visitor.

Virtually all of the data structures are presented in the context of a single, unified, polymorphic class hierarchy. This framework clearly shows the relationships between data structures and it illustrates how polymorphism and inheritance can be used effectively. In addition, algorithmic abstraction is used extensively when presenting classes of algorithms. By using algorithmic abstraction, it is possible to describe a generic algorithm without having to worry about the details of a particular concrete realization of that algorithm.

A secondary goal of the book is to present mathematical tools just in time. Analysis techniques and proofs are presented as needed and in the proper context. In the past when the topics in this book were taught at the graduate level, an author could rely on students having the needed background in mathematics. However, because the book is targeted for second- and third-year students, it is necessary to fill in the background as needed. To the extent possible without compromising correctness, the presentation fosters intuitive understanding of the concepts rather than mathematical rigor.

One cannot learn to program just by reading a book. It is a skill that must be developed by practice. Nevertheless, the best practitioners study the works of others and incorporate their observations into their own practice. I firmly believe that after learning the rudiments of program writing, students should be exposed to examples of complex, yet well-designed program artifacts so that they can learn about the designing good software.

Consequently, this book presents the various data structures and algorithms as complete Java program fragments. All the program fragments presented in this book have been extracted automatically from the source code files of working and tested programs. It has been my experience that by developing the proper abstractions, it is possible to present the concepts as fully functional programs without resorting to pseudo-code or to hand-waving.