How to talk to recruiters at a career fair

A student asking if a company is hiring full-time engineers is not naive in the slightest. You're writing purely from the perspective that all companies behave exactly like Twilio. In my experience (granted this was a couple of years ago), many companies at career fairs are sometimes looking only for interns. Some are just there for some advertisement, not hiring but still maintaining a relationship with the company.

With regards to the point about Java, rather than looking at just the language, I would think it's more worthwhile to see what a person has built with the tools they have knowledge of, rather than extrapolating that they are unwilling to learn something new.

I'm really sick of people saying that you shouldn't wear a suit to a career fair. I understand the implication those who say it are trying to make, but it just doesn't work out that way. Any career fair I have been to, especially when it's for students, the kids dressed down are not doing so because they are confident and talented enough to not worry about impressions. Instead, those are the kids who either did not care enough to prepare for it, possibly have a class assignment that requires going or most often, just take themselves too seriously to be a viable candidate.

Also, to recommend that someone dresses down for the few positions that might be okay with that really limits who the student can meet with. While a few companies may be casual and willing to take someone in who didn't put the time into even preparing themselves for the career fair, many companies (including quite a few bigger companies that would be more likely to hire and invest in new talent) would be turned off immediately.

(on not knowing what specifically you want to work on) "If you are not sure, one good strategy is to rotate - tell one company you'd like to do frontend work, tell the next you'd like to work on mobile and tell the third company you'd like to work on big data. Next summer (or in your spare time) you can try out something different."

...so instead of you just randomly picking what subfield to slot a college hire into, you're asking them to pick randomly and lie about being interested in it?