Timezones and the Java Runtime Environment: Frequently Asked Questions

By the Java SE Platform Support Team, August 2016


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  • Why do I need to care about timezone data?
    Timezone data changes frequently. This is reflected in the rate of change to the Timezone Database and the numbering per year of multiple changes, for example 2007a, b, c, ..., g.
  • Why does timezone data change?
    Timezone settings are adopted locally, and there is no world timezone authority. In North America, timezone adoption occurs at the city or county level. A wide variety of local concerns can drive a municipality to alter their timezone:
    • Large municipal events: For example, the 2006 Commonwealth Games in Sydney.
    • Voting: For example, Brazil altered their setting for national elections one year.
    • Religion: For example, the Egyptian time setting is changing for Ramadan in 2007.
  • Where does one find information about timezones worldwide?
    There is no worldwide timezone data authority, however, the Olson Timezone Database seems to be a point of IT convention. Paul Eggert coordinates the collection of timezone change information and codifies it into the Olson Timezone Database. Paul maintains the Sources for Timezone and Daylight Saving Time Data web site to disperse this timezone information.
  • What exactly is the Timezone Database?
    The Timezone Database is the nearest thing there is to an internationally agreed standard for timezones. For more information about the Timezone Database, see this Wikipedia entry.
  • Which JRE version updates include which versions of the timezone data?
    The versions of the timezone data that are contained in the different JRE version updates are listed on the page Timezone Data Versions in the JRE Software.
  • What are the differences between, for example, "tzdata2005n" and "tzdata2006p"?
    The different  timezone data releases reflect changes in timezone rules that have been applied in different places in the world. Major changes in timezone rules in a particular  timezone data release are described in the page Timezone Data Versions in the JRE Software.
  • Can I still use the deprecated three-letter timezone IDs "EST", "HST", and "MST" for Eastern, Hawaii, and Mountain summer time?
    No, this can lead to incompatibilities. You should use the new format of timezone ID, for example, "America/New_York."
  • What is the minimum version of the Java platform that I need for my country?
    If your international timestamp calculations are important for your applications, then you need to keep your JRE software updated with the most up-to-date timezone rules. To do this, you should upgrade to the latest update release of the JRE software.
  • Do my operating system's timezone patches fix the Java platform's timezone data?
    No. The Java SE platform's timezone data is not read from the local or host operating system. The Java SE platform maintains a private repository of timezone data in locally installed files ( .../jre/lib/zi) as part of the Java Runtime Environment (JRE) software. Applying whatever operating system timezone patches (for example Solaris OS, Linux, Windows) will have no effect on the accuracy of the Java SE platform's timezone data.
  • What happens if I cannot upgrade to a current JRE or JDK version?
    If for any reason it is impossible for you to upgrade your JRE or JDK software to the latest update versions, Oracle provides a tool for updating timezone data in installed JRE or JDK software images. This is called the Timezone Updater tool, or TZUpdater, which is available in Java SE TZUpdater Downloads.
  • What is the TZUpdater tool?
    TZUpdater is a standalone tool that updates older installed JRE implementations with the most recent timezone data. For more information see Timezone Data and the Java Runtime Environment and the TZUpdater README.
  • Where can I get the TZUpdater tool?
    The TZUpdater tool is available in Oracle Technology Network - Java SE Download Page and through My Oracle Support. See Note 1412103.2.
  • Do I need to restart instances of the JRE to pick up new timezone data?

    Yes. Before running the TZupdater tool to update timezone data, you should stop all the relevant instances of the JRE software. Cached instances of timezone data might exist in running JRE software processes if you do not shut down the JRE software before running the tool.

    Restart the JRE software after the TZupdater tool has completed its work.

  • For More Information

    Timezone information specific to the Java platform:

    The following external links provide general information about timezones and DST: