Despite the age and subtitle. This book is still relevant for the Java 6 and 7 platform. The Java Virtual Machine Specification,by Tim Lindholm and Frank Yellin, is a specification book from a pre-Oracle time. The book goes over how the Java language is structured and designed. This is a great guide for any serious Java developer. The book provides insight on the reasons why things are designed the way they are, Java [assembly like] byte code, the classfile format, and a handy reference for the bytecode [including the op codes].
I read this book for non-professional reasons. It was more of a curiosity to read this book. At times, the book went into more detail than I cared about. Also, I skimmed over the documentation on the bytecode. However, I really did like that it introduced the detailed bytecode documentation and then followed it up with examples of how code is transformed into its related bytecode.
Reading this book should make Java Performance (Hunt) a bit easier to read, understand, and more interesting. That is when I can get to reading the book. At the moment, I have more than 30 [physical and non-physical] books on my reading queue.