At just over 6cm (2.5 inches), it's a thick, heavy, book and the spine bends alarmingly as you read it. Despite this it's surprisingly readable, but I wouldn't want to carry it about with me.
This book covers Jini 1.1, and takes great pains to spell out everything you need to do compile and run the examples, as well as listing the code. It's comforting to see complete command lines for Windows and Unix in every case. There are code listings for all of the major areas and a couple of non-trivial worked examples but for a book this size there is not a lot of code. A working knowledge of Java and at least a passing acquaintance with RMI is assumed, but you don't need to know any Jini.
Most of the book is given over to a detailed discussion of the standard Jini services, and how to use them. Each service is covered at two levels - using the basic APIs and using Sun's supplied utility classes. There is also a lot of discussion of the complexities inherent in distributed systems, and how to use Jini to build robust, scalable "self-healing" networks. Scattered through the text are "Core Notes" which offer more detail or different perspectives on the material, and these are always interesting.
Too big for a reference, but a detailed and well-structured book to get you up to speed on Jini quickly and efficiently.