JavaDate

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Instant

• represents a moment, a specific point in the timeline.
• a count of nanoseconds since the epoch of the first moment of 1970 UTC

Instant instant = Instant.now() ; // Capture the current moment in UTC.

LocalDateTime

represents a date and a time-of-day. But lacking a time zone or offset-from-UTC, this class cannot represent a moment. It represents potential moments along a range of about 26 to 27 hours, the range of all time zones around the globe.

ZoneId

• A time zone is represented by the ZoneId class.
• A time zone is a set of rules for handling adjustments and anomalies as practiced by a local community or region.

ZoneId z = ZoneId.of( “Africa/Tunis” ) ;

ZonedDateTime

• ZonedDateTime = ( Instant + ZoneId )

ZonedDateTime zdt = ZonedDateTime.now( z ) ; // Pass a `ZoneId` object such as `ZoneId.of( "Europe/Paris" )`.

java.util.Date

tries to be an instant and dateTime at same time and does both poorly

• It doesn’t have a time zone.
• It doesn’t have a format.
• It doesn’t have a calendar system.
• It rates years as two digits since 1900.
• Months are zero indexed (0 – January, 11 – December)
• All classes in this old API are mutable.