Hi Damu,
It's not mandatory. I know that some people did (Andrew did for sure), while others just documented public ones as stated in the instructions. I think I'll do something between both : document everything in my db, net and util packages while being far less talkative in the GUI part. Would it make any sense to document a private JButton instance named bookButton with something like "This is a button which - when clicked by the user - will call a book method" ?!
Best,
Phil.