Summary

Updating the TZ Data Base to 2024b

Problem

The update to 2024b included:

     Names present only for compatibility with UNIX System V
     (last released in the 1990s) have been moved to 'backward'.
     These names, which for post-1970 timestamps mostly just duplicate
     data of geographical names, were confusing downstream uses.

This includes changes to "EST", "MST", and "HST", i.e., changing those time zones from distinct time zones to links to other time zones. Problem here is, previously they are defined as fixed offset zones, e.g., "EST" is "-05:00" without any DST transitions. With 2024b, "EST" is now a link to "America/Panama." As in the above quote, "America/Panama" has not observed DST since 1970, but offset did change before (i.e., not equal to fixed "-05:00").

In java.time.ZoneId.SHORT_IDS field, they are explictly defined as fixed zones, which should be amended.

Solution

Modify the mappings in ZoneId class. Parsing of the short zone names "EST", "MST", and "HST" is not affected by this change. Also, explictly mention that the mapping may change with the future TZDB updates.

Specification

Change the description for java.time.ZoneId.SHORT_IDS field as:

--- a/src/java.base/share/classes/java/time/ZoneId.java
+++ b/src/java.base/share/classes/java/time/ZoneId.java
@@ -186,15 +186,12 @@
      * This map allows the IDs to continue to be used via the
      * {@link #of(String, Map)} factory method.
      * <p>
-     * This map contains a mapping of the IDs that is in line with TZDB 2005r and
+     * This map contains a mapping of the IDs that is in line with TZDB 2024b and
      * later, where 'EST', 'MST' and 'HST' map to IDs which do not include daylight
-     * savings.
+     * savings since 1970. This mapping may change in update releases in support of new versions of TZDB .
      * <p>
      * This maps as follows:
      * <ul>
-     * <li>EST - -05:00</li>
-     * <li>HST - -10:00</li>
-     * <li>MST - -07:00</li>
      * <li>ACT - Australia/Darwin</li>
      * <li>AET - Australia/Sydney</li>
      * <li>AGT - America/Argentina/Buenos_Aires</li>
@@ -208,10 +205,13 @@
      * <li>CTT - Asia/Shanghai</li>
      * <li>EAT - Africa/Addis_Ababa</li>
      * <li>ECT - Europe/Paris</li>
+     * <li>EST - America/Panama</li>
+     * <li>HST - Pacific/Honolulu</li>
      * <li>IET - America/Indiana/Indianapolis</li>
      * <li>IST - Asia/Kolkata</li>
      * <li>JST - Asia/Tokyo</li>
      * <li>MIT - Pacific/Apia</li>
+     * <li>MST - America/Phoenix</li>
      * <li>NET - Asia/Yerevan</li>
      * <li>NST - Pacific/Auckland</li>
      * <li>PLT - Asia/Karachi</li>