javax vs java package
java, java-package, organization, package
Solution
I think it's a historical thing - if a package is introduced as an addition to an existing JRE, it comes in as `javax`. If it's first introduced as part of a JRE (like NIO was, I believe) then it comes in as `java`. Not sure why the new date and time API will end up as `javax` following this logic though... unless it will also be available separately as a library to work with earlier versions (which would be useful). Note from many years later: it (date and time API) actually ended up being in `java` after all.
I believe there are restrictions on the `java` package - I think classloaders are set up to only allow classes within `java.*` to be loaded from `rt.jar` or something similar. (There's certainly a check in `ClassLoader.preDefineClass`.)
EDIT: While an official explanation (the search orbfish suggested didn't yield one in the first page or so) is no doubt about "core" vs "extension", I still suspect that in many cases the decision for any particular package has an historical reason behind it too. Is `java.beans` really that "core" to Java, for example?
Problem
What's the rationale behind the javax package? What goes into java and what into javax? I know a lot of enterprise-y packages are in javax, but so is Swing, the new date and time api (JSR-310) and other J2SE packages.