javax package contains different packages in two different projects

javax package contains different packages in two different projects

Two projects are open in NetBeans at the same time.
One of the projects is from javaeetutorial5 example zip, it's called
bookstore2. It needs javax.persistence.entity to compile as it uses
@Entity annotation. This one does not build due to javax.persistence not
found. If I typed 'javax.' then persistance would not be in the list.
Another project is a brand new ejb application with a bean and a web. If I
typed 'javax.' then persistence would autocomplete and entity would
autocomplete too. The project builds just fine.
Could the reason be that the brand new project was created by NetBeans
under its projects folder ~/NetBeansProjects, while the example projects
were all unzipped into a subfolder under
~/NetBeansProjects/javaeetutorial5/examples?