Internationalization and Localization - The Java Programming Language - page 1038

You can compare two Calendar objects by using compareTo since Calendar
implements Comparable . If you prefer, you can use the before and after
methods to compare the objects.
24.4.2. Time Zones
TimeZone is an abstract class that encapsulates not only offset from GMT
but also other offset issues, such as daylight saving time. As with oth-
er locale-sensitive classes, you can get the default TimeZone by invoking
the static method geTDefault . You can change the default time zone by
passing setDefault a new TimeZone object to useor null to reset to the
original default time zone. Time zones are understood by particular cal-
endar types, so you should ensure that the default calendar and time
zone are compatible.
Each time zone has a string identifier that is interpreted by the time
zone object and can be displayed to the user. These identifiers use a
long form consisting of a major and minor regional name, separated by
' / '. For example, the following are all valid time zone identifiers: Amer-
ica/New_York , Australia/Brisbane , Africa/Timbuktu . Many time zones have
a short form identifier often just a three letter acronymsome of which
are recognized by TimeZone for backward compatibility. You should en-
deavor to always use the long formafter all, while many people know
that EST stands for "Eastern Standard Time," that doesn't tell you for
which country. TimeZone also recognizes generic identifiers expressed as
the difference in time from GMT . For example, GMT+10:00 and GMT-4:00 are
both valid generic time zone identifiers. You can get an array of all the
identifiers available on your system from the static method getAvail-
ableIDs . If you want only those for a given offset from GMT , you can in-
voke getAvailableIDs with that offset. An offset might, for example, have
identifiers for both daylight saving and standard time zones.
You can find the identifier of a given TimeZone object from getID , and you
can set it with setID . Setting the identifier changes only the identifier on
the time zoneit does not change the offset or other values. You can get
the time zone for a given identifier by passing it to the static method
getTimeZone .