I think you want to know abut the Package concept.
Just it is a naming convention.
Java.something means it is located in the common lib folder but javax.something means it is located in ext lib ..... extra library.
Actually these are nothing but naming convention.
Kind regards,
Dmjpro.
There is more to it: everything stored in the lib/ext doesn't need to be added to
the classpath variable. But you're not allowed to just store everything in there
because only packages that are about to be incorporated in the core classes
set belong in there. It's more than a naming convention, it's a policy.
kind regards,
Jos