Packages / Interfaces / Enumerations and Classes
http://www.j2ee.me/javase/6/docs/api/index-files/index-1.html
http://www.j2ee.me/javase/6/docs/api/java/util/package-summary.html
or
http://java.sun.com/javase/6/docs/api/index-files/index-1.html
Structure
http://java.sun.com/javase/6/docs/
APIs
http://java.sun.com/javase/6/docs/api/overview-summary.html