Re: multiple threads close, wait, join

Hello,

I am writing a world clock in Java. The basic requirements are:
Input is a list of time zones e.g. EST, NZ, UTC
clock ticks on and at the end of each second, prints out 1 line per
time zone
e.g
UTC: 9:50:00 AM
EDT: 5:50:00 AM
NZST: 9:50:00 PM
---
UTC: 9:50:01 AM
EDT: 5:50:01 AM
NZST: 9:50:01 PM

My questions (mostly for my own edification, hopefully useful to other
readers too):

1. I'm thinking of using one thread for each timezone. Prevailing
wisdom seems to indicate that multiple threads, i.e. more than 2X on a
machine with X processors, is generally not useful for performance.
But my idea is this. Each thread (timezone) can sleep(1000)
independently so that at the end of each second of wall-clock-time,
the display can be in relative sync. (This is a simple clock, not
looking for atomic precision.) The question is: does this design sound
sensible or is it just easier to have a single thread sleep for a
second and loop through the time zones and print them out?

2. The next version will be graphical i.e. visualize a simple GUI with
one pane (or graphical equivalent) per time zone that gets refreshed
somewhat synchronously. There's obviously a wealth of material on
designing this sort of thing (I have googled quite a bit about this).
My question is: is there a focused article or tutorial that talks
about how several graphical panes (or windows or whatever) can be
updated simultaneously? How does the multi-thread design affect this?
I'm thinking that each thread can drive its own pane and still
maintain synchronization.

TIA!

Sam N Seaborn