'Fraid I don't have both of the books to hand at the moment, but have a look at these reviews/book descriptions if you like:
Decompiling Java:
Writing for those who want to learn Java by decompilation, Nolan, a specialist in web site optimization, explains how to turn partially compiled Java bytecodes back into source code so that readers can see what the original programmer was thinking. Early chapters unravel the Java classfile format and show how Java code is stored as bytecode and executed by the JVM. Later chapters focus on how to write a Java decompiler, and a final chapter offers case studies.
Both Java and .NET use the idea of a "virtual machine," or VM. And while VMs are useful for some purposes, they undermine the security of your source code, because creation can be reversed, or "decompiled." Which makes this one-of-a-kind book extremely useful: you must understand decompilation, to properly protect your intellectual property.
For example, how secure is your code after you run an obfuscator? The book will answer questions like this, and provide more thorough information about Java byte codes and the Java Virtual Machine (JVM) than any other book on the market. This book redresses the imbalance by providing insights into the features and limitations of today's decompilers and obfuscators, and offering a detailed look at what JVM's actually do.
This is a fantastic in-depth book on decompilers and code obfuscation tools for Java. It covers the structure of Java code files, the opcodes, and the all of the tools required to decompile classes, and to obfuscate existing code. It's an invaluable reference for anyone who has to deploy Java in a non-secure environment, or for those that want to learn how the language really works.
There is a lot of code to pour though, and there are no illustrations. I think the text could have used some illustrations, but that's not a big sticking point for me.
If you are a serious Java gearhead you should have a look at this book. And if you have a specific interest in either de-compiling some Java or obscuring your deployed Java bytecode then this is a must have.
Covert Java:
"Covert Java" provides a fascinating and look at behind the scenes Java development tactics that are usually the domain of seasoned veterans. Definitely a read for those who want to master Java.
--Floyd Marinescu, Author, EJB Design Patterns; General Manager & founder of TheServerSide Communities.
As a Java developer, you may find yourself in a situation where you have to maintain someone else's code or use a third-party's library for your own application without documentation of the original source code. Rather than spend hours feeling like you want to bang your head against the wall, turn to Covert Java: Techniques for Decompiling, Patching, and Reverse Engineering. These techniques will show you how to better understand and work with third-party applications. Each chapter focuses on a technique to solve a specific problem, such as obfuscation in code or scalability vulnerabilities, outlining the issue and demonstrating possible solutions. Summaries at the end of each chapter will help you double check that you understood the crucial points of each lesson. You will also be able to download all code examples and sample applications for future reference from the publisher's website. Let Covert Java help you crack open mysterious codes!