I would like to be as familiar with Java as possible to eventually get into Android game programming. The first Android game programming book I read, while useful, had too much Java in it that I had no clue about. I have finished the Head First Java (2nd edition covering Java 5) and I am ready for Java 7. What do people on these forums that are familiar with Java 7 suggest as a good book?
Anyway, there is a fairly exhaustive looking list of the changes in 6 and 7 starting there. It is still the exact same language, there are just some improvements, bug fixes, extensions, etc. You could certainly look the extensions, such as they are, up at oracle so you get up to speed on the new stuff. I think the only thing that would be even remotely significant to beginners like us is that you can now use strings in switch statements.
So, I think if you buy another book of the same style (how to learn. java) whether it is for version 5 or 7, you will not notice much difference. Maybe a reference would be good, if you want a reference.
$0.02: I looked over about 100 titles at amazon and just read some reviews at the bunkhouse link Jesper de Jong posted. I decided to order "Effective Java" 2nd. It's current for JDK 6. Keep in mind that publishers probably jump on the opportunity to publish JDK 7 books before anyone else. That doesn't mean they will be bad, but I wouldn't use the difference between 6 and 7 as a criteria, just choose a book you think is good for other reasons.