Difference between ZoneOffset.UTC and ZoneId.of(“UTC”)

1. Introduction

Date and time information must be processed accurately in Java, and this involves managing time zones. ZoneOffset.UTC and ZoneId.of(“UTC”) are two standard methods that we can use for displaying Coordinated Universal Time (UTC). While both look like UTC, they have some differences.

In this tutorial, we’ll take an overview of both methods, key differences, and use cases.

2. The ZoneOffset.UTC

The java.time package is introduced from Java 8 and offers classes such as ZoneId and ZoneOffset that we can use to represent time zones. Beyond, the ZoneOffset.UTC is a constant member of the ZoneOffset class. It represents the fixed offset of UTC, which is always +00: 00. This translates to the fact regardless of the season, UTC is the same.

Here’s an example of using ZoneOffset.UTC:

@Test
public void givenOffsetDateTimeWithUTCZoneOffset_thenOffsetShouldBeUTC() {
    OffsetDateTime dateTimeWithOffset = OffsetDateTime.now(ZoneOffset.UTC);
    assertEquals(dateTimeWithOffset.getOffset(), ZoneOffset.UTC);
}

In the above code snippet, we first create an OffsetDateTime object representing the current date and time with the UTC offset. Following, we specify the UTC zone offset (which is zero hours ahead of UTC) using the ZoneOffset.UTC constant. Afterward, the result is verified using the assertEquals() method.

3. The ZoneId.of(“UTC”)

On the other hand, ZoneId.of(“UTC”) creates a ZoneId instance representing the UTC zone. Unlike ZoneOffset.UTC, ZoneId.of(“UTC”) can be used to represent other time zones by changing the zone ID. Here’s an example:

@Test
public void givenZonedDateTimeWithUTCZoneId_thenZoneShouldBeUTC() {
    ZonedDateTime zonedDateTime = ZonedDateTime.now(ZoneId.of("UTC"));
    assertEquals(zonedDateTime.getZone(), ZoneId.of("UTC"));
}

In the above code block, we create a ZonedDateTime object to represent the current date and time in the UTC zone. Then, we use the ZoneId.of(“UTC”) to specify the UTC zone.

4. The Differences and Use Cases

The following table summarizes the key differences between ZoneOffset.UTC and ZoneId.of(“UTC”):

The following table provides use cases for both methods:

5. Conclusion

In conclusion, we take a good overview of the ZoneOffset.UTC and ZoneId.of(“UTC”) methods. Moreover, it is important to distinguish between both methods when handling time zones in Java.

As usual, the accompanying source code can be found over on GitHub.