I'm preparing for SCJA exam. I need to know about packages and classes that is covered in exam's questions.
I need to know all classes from this packages (java.util, javax.swing, ...) or i need to know only about the packages scope and about primitive data types wrappers (and String)?
Stick to the stated exam objectives, and you won't go wrong.
For packages, you just need a high level understanding of what the classes in a given package are. So, know that the swing package is GUI type of components, awt are the older GUI components, java.lang is the core package with your wrapper classes, and utility classes are in java.util.
They won't ask for overwhelming detail on this subject, just the basics.