Instant vs. LocalDateTime: What's the Difference in Java?

The Difference between Instant and LocalDateTime

Despite being similar representations of time and date, Instant and LocalDateTime possess distinct differences.

Instant

An Instant represents a specific moment on the timeline, recorded as nanoseconds since the epoch (January 1, 1970 UTC). It provides a precise timestamp.

LocalDateTime

LocalDateTime, on the other hand, is a date and time-of-day representation without a time zone or offset from UTC. It cannot uniquely identify a moment on the timeline, as it represents a range of potential moments across different time zones.

Misconception

The statement that "LocalDateTime is rather date/clock representation including time-zones for humans" is incorrect. LocalDateTime does not have a time zone or offset, which is crucial for uniquely identifying a moment in time.

Examples of Usage

Instant

• Storing timestamps in databases
• Measuring durations between events
• Performing time calculations

LocalDateTime

Examples where LocalDateTime is suitable include:

• Representing a birthday, which is a fixed date regardless of time zone
• Applying a specific time-of-day across multiple locations (e.g., specifying a meeting time as "12:00 PM" without specifying a time zone)
• Representing appointments where the specific time zone may be unknown or intended

Larger Picture

Understanding Instant and LocalDateTime requires recognizing the broader spectrum of date-time types provided by the java.time framework. These types range from date-only (LocalDate), time-only (LocalTime), time zone-aware (OffsetDateTime), to calendar-aware (YearMonth, MonthDay), and more.

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