> Which classes are the most transparent and easily to use?

I'm not expert in Java GUI applications, so if you ask about
data-aware components (Swing, SWT) I cannot help. But if you think
about persisting data, consider Hibernate. You just develop your
object model using JavaBeans contracts (that's not EJB, only standard
beans) and you specify mapping between your classes and database.
After this persistence happens almost automagically. Check Hibernate
examples at www.hibernate.org.

Roman