How to convert a timestamp to a date

Short answer

A Unix timestamp is the number of seconds since January 1, 1970, UTC. Instant.ofEpochSecond() turns it into a moment:

void main() {
    Instant instant = Instant.ofEpochSecond(1_772_960_400L);
    IO.println(instant);
}

Output:

2026-03-08T09:00:00Z

To local time

To get the date and time in a specific zone, add a ZoneId:

void main() {
    var dateTime = LocalDateTime.ofInstant(Instant.ofEpochSecond(1_772_960_400L), ZoneId.of("Europe/Berlin"));
    IO.println(dateTime);
}

Output:

2026-03-08T10:00

Milliseconds

JavaScript and many APIs give the time in milliseconds — use ofEpochMilli() for them:

void main() {
    IO.println(Instant.ofEpochMilli(1_772_960_400_123L));
}

Output:

2026-03-08T09:00:00.123Z

Back to a number

getEpochSecond() and toEpochMilli() return the timestamp:

void main() {
    var moment = LocalDateTime.of(2026, 3, 8, 9, 0).atZone(ZoneOffset.UTC).toInstant();
 
    IO.println(moment.getEpochSecond());
    IO.println(moment.toEpochMilli());
}

Output:

1772960400
1772960400000

Common mistake

Mixing up seconds and milliseconds. Milliseconds passed as seconds give a date tens of thousands of years ahead:

void main() {
    long millis = 1_772_960_400_000L;
 
    IO.println(Instant.ofEpochSecond(millis));
    IO.println(Instant.ofEpochMilli(millis));
}

Output:

+58152-11-17T00:00:00Z
2026-03-08T09:00:00Z

Thanks for reading!

Short answer

To local time

Milliseconds

Back to a number

Common mistake

Functions used in this recipe

Thanks for reading!