Java examples of the 23 patterns of the classic Gang of Four book [1] are presented in this book. Several other books have done the same, and there are innumerable papers showing specific examples on the Internet. The author does not say what is new in his treatment and I cannot find it either.

To evaluate what he has done, I’ll discuss two of his patterns. The composite pattern embodies two important aspects: the connection of design patterns to analysis patterns, and recursion. Design patterns don’t come out of nowhere; we should first do an analysis model where semantic application aspects are made explicit, leaving out software implementation details. The composite has value because many things in the real world have a similar structure, for example, maps, chemical compounds, language sentences, and bill of materials. All these structures are recursive: a chemical compound is made up of simple (atomic) elements and composite units, which in turn are composed of simple or atomic units. There is nothing of this in this composite pattern, which is an example of whole-part, another (simpler) pattern. Another interesting pattern is the state pattern. This pattern describes the states of an object and the transitions between them produced by events. State machines are not simple, but this book avoids any complexity by showing an example with only two states. The author does not show how to extend this model to a true state machine.

The book does not really show patterns; rather, it shows only examples of pattern solutions. A pattern has a template with several sections indicating its applicability, the problem it solves, the resulting context, and others. Those sections are very important to properly understand and use the pattern. There is no attempt to relate these patterns to domain modeling, software architecture, or security; the patterns are given in a vacuum.

As a professor of computer science who tries to teach his students good software engineering, I cannot recommend this book because it provides a very narrow view of patterns, and many relevant (and important) concepts are ignored or wrong. Practitioners cannot ignore the basic principles of software engineering if they want to produce good quality systems.

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