The O'Reilly book "Java in a Nutshell" includes a very well-written overview of what every Java class does together with a terse listing of its methods. It's almost always advisable to read the Nutshell description before using a class although Googling the JavaDoc page for the class is also a useful complementary strategy.
Bookshare users can get an electronic copy of the 5th edition (as well as older editions) of the Nutshell book from Bookshare for free. This edition covers the important new stuff in Java 5 including generics. If I were only going to own one book about Java, this would definitely be it.
By the way, working with collections is one of the more sophisticated aspects of Java so it's not an optimal starting point for leaning Java.
Best wishes,Susan Jolly
