Joda Time is brilliant.
It's a pleasure to use, and obviously was created by people who thought long and hard about it, and had suffered with the problems of the standard Java date/time libraries.
If you still use Date or Calendar, then check out Joda Time.
$ ping facebook.com
PING facebook.com (184.108.40.206): 56 data bytes
64 bytes from 220.127.116.11: icmp_seq=0 ttl=87 time=59.217 ms
64 bytes from 18.104.22.168: icmp_seq=1 ttl=87 time=58.550 ms
64 bytes from 22.214.171.124: icmp_seq=2 ttl=87 time=58.887 ms
--- facebook.com ping statistics ---
"Inquiry is fatal to certainty." -- Will Durant