There's no guarantee that there's documentation anywhere for any given
Java class. Sun is careful to document everything and publish the documentation in well-known locations, but Joe Developer may not be.
All the package names that start with java or javax are from Sun and are documented in the JDK and on Sun's web site. Anything else (with the exceptions of some org.xml packages, and a few others) come from someplace else, and you have to consult the individual vendor for documentation.