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There are three options as far as I know:
- Ask the user.
- Use the IP and a geolocation database to guess what the user's location and
hence timezone is.
I kinda forgot about Java applets, if he's making one then it's easiest to get it
from there. I also think that if he made one he wouldn't ask this question, so
if he's doing Java stuff it's probably server-side only.
I'm very happy that bloated things like client-side Java seem to be disappearing
(at least I've Java disabled and never notice missing it). The last thing we need
is Silverlight spreading around. Flash is bad enough already.