Java Instant

last modified July 10, 2024

In this article we show how to use Instant to define moments in time in Java.

Instant represents a specific moment in time on the timeline. It’s akin to a single point on a never-ending line. Unlike other date and time classes, Instant doesn’t inherently include time zone information. Instead, it measures time as the number of seconds and nanoseconds elapsed since a specific point in time, known as the epoch.

The epoch is January 1st, 1970, at 00:00:00 Coordinated Universal Time (UTC). Positive Instant values represent times after the epoch, while negative values indicate times before.

Common use cases for Instant include:

- Recording timestamps for events within an application.

- Storing timestamps in databases where UTC is the preferred time format.

Performing calculations based on the number of seconds or nanoseconds elapsed
    since a specific point in time.

Current timestamp

We get the current timestamp with Instant.now.

Main.java

import java.time.Instant;

void main() {

var timestamp = Instant.now();
System.out.println("The current timestamp: " + timestamp);

}

The example prints the current timestamp.

$ java Main.java The current timestamp: 2024-07-10T14:37:39.890616200Z

Unix time

Unix time (also known as POSIX time or epoch time) is a system for describing a point in time, defined as the number of seconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970, minus the number of leap seconds that have taken place since then.

Main.java

import java.time.Instant;

void main() {

Instant now = Instant.now();

long unixTime = now.toEpochMilli();
System.out.println(unixTime);

}

We compute the current Unix time in milliseconds.

$ java Main.java 1720623471356

The plus/minus methods

The plus/minus methods can be used to add datetime units to the instant.

Main.java

import java.time.Instant; import java.time.temporal.ChronoUnit;

void main() {

var timestamp = Instant.now();

var res = timestamp.plus(5, ChronoUnit.DAYS);
System.out.println(res);

res = timestamp.plusSeconds(78566);
System.out.println(res);

res = timestamp.minus(57, ChronoUnit.HOURS);
System.out.println(res);

}

The example gets the current instant and adds 5 days, 78566 seconds, and subtracts 57 hours.

$ java Main.java 2024-07-15T14:42:46.830593700Z 2024-07-11T12:32:12.830593700Z 2024-07-08T05:42:46.830593700Z

Formatting Instant

We use DateTimeFormatter to format instants.

Main.java

import java.time.ZoneId; import java.time.format.DateTimeFormatter;

void main() {

var timestamp = Instant.now();
System.out.println(timestamp);

DateTimeFormatter df1 = DateTimeFormatter.ISO_DATE_TIME.withZone(ZoneId.of("UTC"));
System.out.println(df1.format(timestamp));

DateTimeFormatter df2 = DateTimeFormatter.RFC_1123_DATE_TIME.withZone(ZoneId.of("UTC"));;

System.out.println(df2.format(timestamp));

}

Since Instant does not include date or time components, only represents a point in time, we add the zone with withZone(ZoneId.of(“UTC”)).

$ java Main.java 2024-07-10T14:51:09.957078500Z 2024-07-10T14:51:09.9570785Z[UTC] Wed, 10 Jul 2024 14:51:09 GMT

Converting to LocalDateTime

In the following example we show how to convert an Instnt to LocalDateTime.

Main.java

import java.time.Instant; import java.time.LocalDateTime; import java.time.ZoneId;

void main() {

Instant now = Instant.now();

LocalDateTime localDateTimePST = LocalDateTime.ofInstant(now, ZoneId.of("Europe/Bratislava"));
System.out.println("Current time in Bratislava: " + localDateTimePST);

}

In the example we convert the Instant to LocalDateTime for a specific time zone (Europe/Bratislava).

$ java Main.java Current time in Bratislava: 2024-07-10T16:54:46.319805200

Source

Java Instant - language reference

In this article we have used Java Instant to define moments in time.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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