The title of this book is very misleading, the word `Java' being used to boost sales. The language could have been any procedural language and only accounts for some 0.1% of the understanding of the OPEN methodology presented. The book itself is reasonably well written as a tutorial, but is not going to be much use as a reference work.
The OPEN methodology is a contender against UML, being very similar in aims and scope; it is a little better thought out in some areas, lacking in others. The back of the book actually suggests that you could attempt to use the book (&the OPEN method) to learn Java - how is completely beyond me, the only Java is a few function prototypes, which happen to be grouped into what could be implemented as classes, it could be C or Assembler, albeit with an OO bent. The CD-ROM contains 4.25Mbytes of the Java (and the corresponding Smalltalk) source code, supposedly `designed' by the use of the OPEN method over the given requirements - I'm not convinced.
If you need to learn the OPEN methodology, or want to find ways to improve your use of UML, then this is a good tutorial. If this book were titled 'Learn OPEN in 21 days' I'd recommend it.