A TimeZone is a Java class for a region of the earth that keeps the same time.
Spelling is chaotic. The Java class is spelled precisely TimeZone. When you see that
spelling on this website, you know I am referring to the Java class. Authorities say that time
zone, timezone and time-zone are all correct. You will
more frequently see timezone in the USA and time-zone in
Britain, however, I have discovered from study google hits, that most people including the Americans and Brits
use time zone. I attempt to use the time zone spelling
consistently on this web site.
What are Time Zones
If the people in a given time zone keep different time in summer and winter, everyone is the region flips
together. The TimeZone class describes the offset from UTC (Coordinated Universal Time/Temps Universel Coordonné) in summer and winter time
and when the flips occur of a given time zone. To get the default TimeZone adjusted
for the user’s location:
In ordinary use, a time zone is a region of the earth that keeps the same winter
time. They may or may not all flip to summer time at the same time and some parts may not flip at all.
TimeZone Names and Offsets
The names for time zones used in Java comes from a database maintained by Arthur David Olson. For reasons only he understands, Pacific Standard Time is called America/Los_Angeles.
The reason that local time is different at different spots on the earth is a consequence of:
The reason we have time zones is to make synchronising railway (and later airline and TV)
schedules easier. If we used natural time, based on observing the instant the sun were highest in the sky, every
town would have its own slightly different clock from its immediate neighbours. This is how things used to be
done in the days of the stagecoach.
- The earth rotates on its axis.
- The earth rotates counter-clockwise when viewed looking down on the north pole.
- The earth rotates west to east.
- The sun rises in the east and sets in the west.
- In natural time, noon is when the sun is highest in the sky. This happens at one instant each day and at a
different instant each day for each degree of latitude.
- People back east get up earlier and go to bed earlier.
You will see many different ways of specifying a time zone, including:
- Olson: America/Vancouver
- Posix: PST8PDT
- UTC relative UTC-8 UTC-7
Here is a list of available TimeZones:
If, TZ, the above TimeZone Java Applet (that can also be run as an application) does not work…
Get New Java Get New Browser
- If Copy/Paste (Ctrl-C/Ctrl-V) do not work, you can turn them back on by
modifying your java.policy file. This is not for the novice or faint of heart. instructions
Your alternative is to download this program and run it without a browser.
- Often problems can be fixed simply by clicking the reload button on your browser.
- This Java Applet (that can also be run as an application) needs 32-bit (not 64-bit) Java 1.6 or later.
For best results use the older 1.7.0_17 not the latest buggy 1.7.0_21.
In the Java Control Panel, configure medium security to allow vanilla unsigned applets to run.
- You also need a recent browser.
- It works under any operating system that supports Java e.g. W2K/XP/W2003/Vista/W2008/W7-32/W7-64/W8-32/W8-64/Linux/LinuxARM/LinuxX86/LinuxX64/Ubuntu/Solaris/SolarisSPARC/SolarisSPARC64/SolarisX86/SolarisX64/OSX
- You should see the Applet hybrid above looking much like this screenshot. If you don’t, the following hints should help you get it working:
- Especially if this Applet hybrid has worked before, try clearing the browser cache and rebooting.
- To ensure your Java is up to date, check with Wassup. First, download it and run it as an application independent of your browser, then run it online as an Applet to add the complication of your browser.
- If the above Applet hybrid does not work, check the Java console for error messages.
- If the above Applet hybrid does not work, you might have better luck with the downloadable version available below.
- If you are using Mac OS X and would like an improved Look and Feel, download the QuaQua look & feel from randelshofer.ch/quaqua. UnZip the contained quaqua.jar and install it in ~/Library/Java/Extensions or one of the other ext dirs.
- If you are using Microsoft Internet Explorer 7, 8 or 9, try another browser. Seriously. Microsoft has taken great pains, over and over, to screw up Java and every other multi-platform standardisation.
- If you are using Microsoft Internet Explorer 7, 8 or 9, you must click to allow blocked content permission for Active X to run. This also gives permission to Java to run. Click the Information bar, and then click Allow blocked content. Unfortunately, this also allows dangerous ActiveX code to run. However, you must do this in order to get access to perfectly-safe Java Applets running in a sandbox. This is part of Microsoft’s war on Java. Don’t put up with it! Use a different browser.
- If you are using Microsoft Internet Explorer 9, makes sure the Java Plug-In SSV helper add-in is installed and enabled.
If it is not, try reinstalling the Java JRE.
- If you have Windows 7 64-bit
and Internet Explorer 64-bit,
in theory you can use 64-bit Java,
but I never been able to get it to work.
- Try upgrading to a more recent version of your browser, or try a different browser e.g. Firefox, SeaMonkey, Safari or Avant.
- If you still can’t get the program working click HELP for more detail.
- If you can’t get the above Applet hybrid working after trying the advice above and from the HELP button below, have bugs to report or ideas to improve the program or its documentation, please send me an email at.
- Add column 1 in hours to UTC to get local standard time.
- Add column 2 in hours to UTC to get local daylight saving time.
- Use UTC when you want no time zone at all.
- Use Asia/Riyadh for Arabia
Standard Time. Asia/Riyadh87, Asia/Riyadh88
and Asia/Riyadh89 are 3 hours and 7 minutes east
of UTC. This is the offset used in 1987 to 1989.
Actually it was 3 hours 7 minutes and 4 seconds to approximate solar time. Prior
to 1950 they used 3:06:52. In the period 1951—
1986 and 1990 onward they
used a simple 3 hour difference. In Islamic tradition, the day starts at sunset.
- Note how much many aliases there are for the same time zone. I speculate there
are two reasons for this:
- To anticipate some geographical region adopting a quirky daylight saving rule in
future. There would be no need adjust to a new split time zone to adopt the new
rule. Only the tables built into Java would need to be adjusted.
- It makes it easier for people to find their own time zone. They need find only a
nearby city without having to consult a map to find a distant city on the same
longitude. Often they can find their own city directly.
- Timezone names never contain spaces. They use underscores, e. g. America/Los_Angeles. In Linux, make sure
/etc/sysconfig/clock use official underscore names.
- Use UTC rather that GMT (Greenwich Mean Time) for the base time used
internally. GMT is London civil time and has a DST (Daylight Saving Time) correction in summer. UTC huh not CUT? It was a
weird compromise acronym half way between French and English. GMT stands for GMT.
See GNU Timezone classes that correct for historical
changes and leap seconds.
You can find out the current time at any place on the globe at WorldTimeServer.com. It will tell you the offset from UTC, but not the time
huh not CUT? It was a
weird compromise acronym half way between French and English.
Unfortunately, you can’t extract the rules about when daylight savings go into effect from a
TimeZone object. I suppose if you were patient you could deduce them by binary search
on inDaylightTime. You could also study the code that is used to construct all the
TimeZone objects in rt.jar, or the various locale jars and
decompile and parse that to extract the information.
Here are the rules for the switch
days in the EU. There are some algorithms to compute them.
Switch days are decided politically so can change erratically, especially in the USA, albeit with advance
notice. In ancient Rome, one could bribe officials to have months lengthened or shortened, so we have made
Olson Timezone Database
An ordinary citizen, David Olson
has maintained a database of timezone and DST trivia that was used by the entire computing community.
It was a much bigger job than you might imagine. Have a look at some of the changes in
He has retired his server because a mean-spirited astrology company,
Astrolabe, sued him distributing data free they sell.
This information is clearly in the public domain.
It is no secret when DST stops and starts and how far off UTC each spot on earth was at various times in the past. He did not have the resources
to fight back. So for now, there is no one keeping track! Perhaps Anonymous could punish Astrolabe for this evil deed.
Perhaps Oracle could sue them for selling their timezone data.
These turkeys attempted to screw Microsoft, Oracle, AT&T (American Telephone & Telegraph), the airlines, the railroads
and every operating system/computer program that deals with local time.
They all rely directly or indirectly on the Olson tables. All went well and Astrolabe was handily defeated.
Oracle’s Javadoc on TimeZone
class : available: