zoneId

ZoneId is a class in the Java time API (java.time) that represents a time zone identifier. It encodes the rules that determine how a region’s local time relates to Coordinated Universal Time (UTC), including how offsets may change during daylight saving time. ZoneId is immutable and thread-safe, and it is used to convert instants or local dates and times into the appropriate local representation for a given region.

Zone identifiers come from the IANA Time Zone Database. The most common forms are region-based IDs such as Europe/Paris or America/New_York, which carry historical and future rules for offsets and daylight saving. ZoneId can also represent a fixed offset, using IDs like +02:00, which correspond to a constant UTC offset without any daylight saving behavior. The ZoneId.of method accepts both region-based IDs and offsets, returning a ZoneId object.

Key relationships and usage: ZoneId works with other parts of the time API, notably ZonedDateTime, LocalDateTime, and Instant. You can obtain a zone with ZoneId.systemDefault(), ZoneId.of("UTC"), or ZoneId.of("Asia/Kolkata"). The getId method returns the string identifier, and getRules returns the ZoneRules that describe valid offsets for instants in that zone. Using a ZoneId to create a ZonedDateTime ensures correct local interpretation of times across different zones and helps perform accurate conversions between instants and local times.

Limitations and scope: ZoneId identifiers are drawn from the IANA database, which means available IDs may vary by platform and JRE version. Some legacy or alias IDs may be deprecated in favor of explicit region-based IDs.