Oracle's page on JDeveloper is probably the least informative product information page I ever saw...
JDeveloper started out as a custom build of JBuilder 2.0 and has since evolved a bit to keep pace.
But it's still not much more than a
Java IDE, and certainly no match for JBuidler Studio which includes a whole range of other tools (never mind that you will likely not use most of them).
Together Control Centre has limited editing capability built in, but is certainly no substitute for JBuilder (just as the UML capabilities in JBuilder are no substitute for Together).
As a student especially I'd not bother with all those tools. Focus on the language and processes rather than on the tools and you'll be a lot better off in the real world where you're likely to have to work with different tools.
If you focus on learning the tools you'll not learn the process proper and have great difficulty working in an environment where different tools are used and/or the processes are applied differently from your experience.