Sorry, Andrew, I wasn't really trying to ask that as it's own question. It was more of a rhetorical question. My point was more my second statement:
I guess what I'm wondering if the book's example is planting seeds of non-existent requirements simply because the book's author choose to do something a certain way.
So, regarding the previous poster saying that your PostiveIntegerField code could be copied directly, I was trying to point out there is nothing in the assignment saying that the checking done by PositiveIntegerField is necessary which supports your point about book's code being more difficult than the Sun assignment.
IMO, in that case, the book solution is going above and beyond the call of duty, but I don't think it qualifies as giving "too much information" since the information is not even really required! I do wonder, though, if those kinds of more intricate details will trip up the more inexperienced developer and make them think that is required even if it isn't!
FWIW, I've been coding Java for 11 years but most of my experience, but I haven't done anything regarding RMI or sockets for 10 years so I found the chapters covering those topics to be really useful. The rest of the design ideas closely mirrored what I had already planned to do based on my own reading of the assignment. I think that if someone was new to Java, they would have a harder time understanding all of the code and explanations in the book and would, at the least, take a much longer time to complete the project. Also, I'm sure most of the information in the book could be gleamed from other sources. It would just take longer to find it all that way so the book becomes "one stop shopping" for the relevant info.