Changes to Daylight Saving Time

Changes to Daylight Saving Time and the impact on IBM SDK for Java and Java Runtime Environments

Find out how changes to Daylight Saving Time (DST) affect IBM SDKs and JREs and how these changes are applied to Java code. Learn about the resources available to help you address potential problems with your java applications.

Why are changes to DST significant?

Many countries around the world use a Daylight Saving Time convention. Typically, clocks move forward by one hour during the summer months to create more daylight hours during the afternoon and less during the morning. This practice has many implications, including the need to adjust system clocks in computer systems. Occasionally, countries change their DST start and end dates. These changes can affect the date and time functions in applications, because the original start and end dates are programmed into the operating system and in Java software. To avoid this problem you must update operating systems and Java™ installations with the new DST information.

How time zone updates are implemented in Java?

The Olson time zone database is an external resource that compiles information about the time zones around the world. This database establishes standard names for time zones, such as "America/New_York", and provides regular updates to time zone information that can be used as reference data. To ensure that Java JREs and SDKs contain up to date DST information, IBM incorporates the latest Olson update into each Java service refresh. To find out which Olson time zone update is included for a particular Service Refresh, see Olson time zone updates for Java JRE and SDK service refreshes for IBM products.

Updating your SDK and JRE

When changes to Daylight Saving Time are announced, you must consider whether your systems or applications will be affected. This assessment will help you decide how quickly you need to apply an update to your operating system and your Java SDKs or JREs. To assess your systems and understand the actions you need to take, see Guidance on updating Java SDKs and JREs for DST changes.

If you require a long lead time to update to the latest Java service refresh, but need to apply the DST changes to your Java installation as quickly as possible, you can use the IBM Time Zone Update Utility for Java, also known as JTZU. This tool applies DST changes directly to a Java environment. For more information about JTZU and to download the latest level, see IBM Time Zone Update Utility for Java Download page.