Re: java installation
Per your screen capture I think you've got it. That src.zip archive is the one NetBeans uses (and it usually is found by default). That zipped api doc is the code-completion feature.
You can also link to the online api docs using in NetBeans Tools -> Java Platforms [TAB] JavaDoc [Button] Add URL
or download the actual arhive as a zip (it also will be src.zip) and link in the same Dialog window.
So, that should help you if you were wanting code-completion feature. I keep a bookmark to the Oracle API docs to view in my browser for reference.
"You don't do art because you want to, no, you do art because you have to." -- M. Buonarroti