Java Instant Examples

1. Introduction

In this tutorial, we explore the Instant class in Java, which represents a moment on the timeline in UTC. This class is part of the java.time package, introduced in Java 8, and is used to handle an instantaneous point on the time-scale.

Key Points

1. Creating an Instant from the current timestamp and from a string representation.

2. Manipulating Instant by adding or subtracting time.

3. Comparing two Instant objects to determine their temporal order.

4. Calculating the difference between two Instant objects.

5. Converting between Instant and other date-time classes like LocalDateTime, ZonedDateTime, and OffsetDateTime.

2. Program Steps

1. Create an Instant representing the current moment and from a string.

2. Add and subtract time to/from an Instant.

3. Compare Instant objects to check if one is before or after another.

4. Calculate the difference in seconds between two Instant objects.

5. Convert an Instant to LocalDateTime, ZonedDateTime, and OffsetDateTime and back.

3. Code Program

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.time.temporal.ChronoUnit;

public class Main {

    public static void main(String[] args) {

        // get an Instant
        Instant timestamp = Instant.now();
        System.out.println("Timestamp: " + timestamp);

        // String to Instant
        Instant timestampFromString = Instant.parse("2019-02-24T14:31:33.197021300Z");
        System.out.println("\\nTimestamp from string: " + timestampFromString);

        // Plus two hours
        Instant twoHourLater = Instant.now().plus(2, ChronoUnit.HOURS);
        System.out.println("\\nTwo hours later: " + twoHourLater);

        // Minus 10 minutes
        Instant tenMinutesEarlier = Instant.now().minus(10, ChronoUnit.MINUTES);
        System.out.println("Ten minutes earlier: " + tenMinutesEarlier);

        // check if one Instant is after another Instant
        Instant timestamp1 = Instant.now();
        Instant timestamp2 = timestamp1.plusSeconds(10);
        boolean isAfter = timestamp1.isAfter(timestamp2);
        System.out.println("\\n" + timestamp1 + " is " + (isAfter ? "" : "not ") + "after " + timestamp2);

        // check if one Instant is before another Instant
        boolean isBefore = timestamp1.isBefore(timestamp2);
        System.out.println(timestamp1 + " is " + (isBefore ? "" : "not ") + "before " + timestamp2);

        // difference between two Instants
        long difference = timestamp1.until(timestamp2, ChronoUnit.SECONDS);
        System.out.println("Between " + timestamp1 + " and " + timestamp2 + " there are " + difference + " seconds");

        // convert Instant to LocalDateTime
        LocalDateTime ldt = LocalDateTime.ofInstant(Instant.now(), ZoneOffset.UTC);
        System.out.println("\\nInstant to LocaleDateTime: " + ldt);
        // convert LocalDateTime to Instant
        Instant instantLDT = LocalDateTime.now().toInstant(ZoneOffset.UTC);
        System.out.println("LocaleDateTime to Instant: " + instantLDT);

        // convert Instant to ZonedDateTime
        ZonedDateTime zdt = Instant.now().atZone(ZoneId.of("Europe/Paris"));
        System.out.println("Instant to ZonedDateTime: " + zdt + " (offset: " + zdt.getOffset() + ")");
        // convert ZonedDateTime to Instant
        Instant instantZDT = LocalDateTime.now().atZone(ZoneId.of("Europe/Paris")).toInstant();
        System.out.println("ZonedDateTime to Instant: " + instantZDT);

        // convert Instant to OffsetDateTime
        OffsetDateTime odt = Instant.now().atOffset(ZoneOffset.of("+02:00"));
        System.out.println("Instant to OffsetDateTime: " + odt + " (offset: " + odt.getOffset() + ")");
        // convert OffsetDateTime to Instant
        Instant instantODT = LocalDateTime.now().atOffset(ZoneOffset.of("+02:00")).toInstant();
        System.out.println("OffsetDateTime to Instant: " + instantODT);
    }
}

Output:

Timestamp: 2021-11-10T12:49:11.236292200Z
Timestamp from string: 2019-02-24T14:31:33.197021300Z
Two hours later: 2021-11-10T14:49:11.304788800Z
Ten minutes earlier: 2021-11-10T12:39:11.304788800Z
2021-11-10T12:49:11.304788800Z is not after 2021-11-10T12:49:21.304788800Z
2021-11-10T12:49:11.304788800Z is before 2021-11-10T12:49:21.304788800Z
Between 2021-11-10T12:49:11.304788800Z and 2021-11-10T12:49:21.304788800Z there are 10 seconds
Instant to LocaleDateTime: 2021-11-10T12:49:11.305785800
LocaleDateTime to Instant: 2021-11-10T18:19:11.338699600Z
Instant to ZonedDateTime: 2021-11-10T13:49:11.338699600+01:00[Europe/Paris] (offset: +01:00)
ZonedDateTime to Instant: 2021-11-10T17:19:11.347674900Z
Instant to OffsetDateTime: 2021-11-10T14:49:11.356655100+02:00 (offset: +02:00)
OffsetDateTime to Instant: 2021-11-10T16:19:11.357650400Z

Explanation:

1. Instant.now() creates an Instant representing the current moment.

2. Instant.parse("2019-02-24T14:31:33.197021300Z") creates an Instant from a formatted string.

3. Instant.now().plus(2, ChronoUnit.HOURS) calculates two hours later from the current instant.

4. Instant.now().minus(10, ChronoUnit.MINUTES) calculates ten minutes earlier from the current instant.

5. timestamp1.isAfter(timestamp2) checks if timestamp1 is after timestamp2.

6. timestamp1.isBefore(timestamp2) checks if timestamp1 is before timestamp2.

7. timestamp1.until(timestamp2, ChronoUnit.SECONDS) calculates the difference in seconds between two instants.

8. LocalDateTime.ofInstant(Instant.now(), ZoneOffset.UTC) converts an Instant to LocalDateTime.

9. LocalDateTime.now().toInstant(ZoneOffset.UTC) converts LocalDateTime to an Instant.

10. Instant.now().atZone(ZoneId.of("Europe/Paris")) converts an Instant to ZonedDateTime.

11. LocalDateTime.now().atZone(ZoneId.of("Europe/Paris")).toInstant() converts ZonedDateTime to an Instant.

12. Instant.now().atOffset(ZoneOffset.of("+02:00")) converts an Instant to OffsetDateTime.

13. LocalDateTime.now().atOffset(ZoneOffset.of("+02:00")).toInstant() converts OffsetDateTime to an Instant.


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