[LINK] - Sun and 3rd party Java API Links

Sun Java API reference:
http://java.sun.com/reference/api/index.html

DOCJAR Contains a lot of third party java library and source code:
http://www.docjar.com/

HIBERNATE - Relational Persistence for Idiomatic Java
http://www.hibernate.org/hib_docs/reference/en/html/index.html