I am very disappointed with the new version 7 of Opera. Until this version came out, I was a big fan and would have recommended it highly but now, well, not so. There are things in it that do not function in the same way, or even at all, as other browsers and that in itself puts me off using it.
To answer your question, it used to be that if you already had Java installed the Opera download would take that into account. So, download the "with Java" version and let it sort itself out.