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LocalDateTime

LocalDateTime encapsulates both date and time information, with no time zone.

The overloaded of method allows you pass: * Year as an int, * Month, as a month number from 1 to 12, or Month enum value, * Day, hour and minute integers, * Optional seconds, with optional nanoseconds.

... or use an overload that takes LocalDate and LocalTime objects.

LocalDateTime ldt = LocalDateTime.of(2018, 12, 25, 7, 30);
LocalDate christmas = LocalDate.of(2018, 12, 25);
LocalTime sevenThirty = LocalTime.of(7, 30);
LocalDateTime xmasMorning = LocalDateTime.of(christmas, sevenThirty);
  • ISO-8601 format for a datetime is YYYY-MM-DDThh:mm:ss
System.out.println(xmasMorning);
// "2018-12-25T07:30"

ZonedDateTime

As the name implies, a LocalDateTime represents the time as seen on a local wall clock.

Like LocalDateTime, a ZonedDateTime encapsulates a calendar date and clock time, but the clock time is associated with a specific time zone.

ZonedDateTime coloradoDay = ZonedDateTime.of(2018, 8, 1, 0, 0, 0, 0, ZoneId.of("UTC-6"));
System.out.println(coloradoDay);
// "2018-08-01T00:00-06:00[UTC-06:00]"

Practice Exercise

Time zone IDs can be expressed in multiple ways: * Hour offsets relative to UTC (Universal Coordinated Time, aka Greenwich Mean Time, aka Zulu or Z): * Z-7 * Z+1 * Prefixed offset IDs: * GMT-7 * UTC+1:00 * Regional IDs: * MST (Mountain Standard Time) * CET (Central European Time) * Names: * US/Mountain, America/Denver * Europe/Paris

java.time.ZoneId can parse most of these.

Instant

When interfacing with systems based on Unix times, use an Instant object.

Instant thisInstant = Instant.now();
System.out.println(thisInstant.getEpochSecond());
// 1517958836

You can convert an Instant to a LocalDateTime or ZonedDateTime by providing a time zone ID.

ZonedDateTime thisZonedDateTime = ZonedDateTime.ofInstant(thisInstant, ZoneId.of("US/Mountain"));
System.out.println(thisZonedDateTime);
// "2018-02-06T16:12:15.573-07:00[US/Mountain]

Drill

DatesAndTimes/com.example.datesandtimes.drills.TimeDrill

In main: * Create a LocalDateTime for the current date and time. * What happens if you use the LocalDateTime above to create a LocalDateTime for 22 hours in the future?

(Solution: DatesAndTimes/com.example.datesandtimes.solutions.drills.TimeDrill2)

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