As the title suggests, Java 2 Performance and Idiom Guide deals with performance techniques and idioms in Java. In more detail, it breaks down like this: 

• The book contains three chapters (100+ pages) devoted to performance issues, from high-level design techniques that can have a significant impact on the performance to fine-grained implementation tips that have only moderate to minor impact.
• The next-largest section (70+) deals with Java library idioms. It covers the universal super class java.lang.Object, reflection, concurrency, collections, resources, and exceptions.
• Three shorter chapters follow (around 20 pages each) and cover language idioms, packaging idioms, and testing idioms.
• The book closes with a section on coding idioms (roughly 50 pages) dealing with naming and style conventions. 

For this reason, the section on Java design and implementation idioms leaves much to be desired, while the section on performance techniques, to our knowledge, is one of the best collections of Java-relevant performance techniques currently available in book form. Unfortunately, Java performance is a fast-moving area and, as the authors themselves point out, for some techniques like JIT compilers or Hot Spot technology, Java 2 Performance and Idiom Guide can give only a snapshot of the current situation. It will be outdated soon. 

We also noticed that the book, despite its title, includes a number of general - that is, non-Java-specific - idioms. For example, the section about performance offers advice like "use buffered I/O" or "move loop invariants out of the loop." This kind of advice might be welcome to novice programmers, but an experienced software engineer will not find anything new or Java-specific in these idioms. 

In sum, Java 2 Performance and Idiom Guide is a good starting point for software engineers or programmers who are relatively new to Java and want to get a broad overview of idioms and performance techniques relevant to Java. While the performance issues are discussed adequately, the reader should not expect deep, detailed explanations of Java idioms. Only a title specifically devoted to a certain Java issue will deliver this type of coverage. For example, the reader will not get the same understanding of concurrency and multi-threading idioms in Java from the 22 pages devoted to the issue in this book as he or she would get from Doug Lea's more-than-400-page book, Concurrent Programming in Java . 

Angelika Langer develops and teaches classes on advanced C++, STL, multithreading, internationalization, and Java. She served on the ANSI/ISO C++ Committee from 1993 to 1998. Klaus Kreft is a software architect and consultant with 15+ years of experience in industrial software development. He works for Siemens Business Services in Germany. Langer and Kreft are authors of "Standard C++ IOStreams and Locales: Advanced Programmer's Guide and Reference" (Addison-Wesley, 1999) and are columnists for C++ Report magazine.