The forums in the
JDC (free registration required) seem to be popular but I don't actually hang out there to speak for quality of discussion or help.
Since CS courses are typically targeted (i.e. a specific curriculum and assignments), getting assistance from classmates and TAs is perhaps preferential. There could well be a newsgroup just for the course.
Some of us here have the willingness and aptitude to give good Java advice, but it doesn't necessarily occur in a timely matter. I wouldn't mind knowing of good professional Java-related forums out there.