Module java.base
Package java.time

Interface InstantSource

All Known Implementing Classes:
Clock
public interface InstantSource
Provides access to the current instant.

Instances of this interface are used to access a pluggable representation of the current instant. For example, InstantSource can be used instead of System.currentTimeMillis().

The primary purpose of this abstraction is to allow alternate instant sources to be plugged in as and when required. Applications use an object to obtain the current time rather than a static method. This can simplify testing.

As such, this interface does not guarantee the result actually represents the current instant on the time-line. Instead, it allows the application to provide a controlled view as to what the current instant is.

Best practice for applications is to pass an InstantSource into any method that requires the current instant. A dependency injection framework is one way to achieve this: 

  public class MyBean {
    private InstantSource source;  // dependency inject
    ...
    public void process(Instant endInstant) {
      if (source.instant().isAfter(endInstant) {
        ...
      }
    }
  }
This approach allows an alternative source, such as fixed or offset to be used during testing.

The system factory method provides a source based on the best available system clock. This may use System.currentTimeMillis(), or a higher resolution clock if one is available.

Since:
17

  • Method Summary

    Modifier and Type
    Method
    Description
    static InstantSource
    fixed(Instant fixedInstant)
    Obtains a source that always returns the same instant.
    Instant
    instant()
    Gets the current instant of the source.
    default long
    millis()
    Gets the current millisecond instant of the source.
    static InstantSource
    offset(InstantSource baseSource, Duration offsetDuration)
    Obtains a source that returns instants from the specified source with the specified duration added.
    static InstantSource
    system()
    Obtains a source that returns the current instant using the best available system clock.
    static InstantSource
    tick(InstantSource baseSource, Duration tickDuration)
    Obtains a source that returns instants from the specified source truncated to the nearest occurrence of the specified duration.
    default Clock
    withZone(ZoneId zone)
    Returns a clock with the specified time-zone.

  • Method Details

    • system

      static InstantSource system()
      Obtains a source that returns the current instant using the best available system clock.

      This source is based on the best available system clock. This may use System.currentTimeMillis(), or a higher resolution system clock if one is available.

      The returned implementation is immutable, thread-safe and Serializable.

      Returns:
      a source that uses the best available system clock, not null

    • tick

      static InstantSource tick(InstantSource baseSource, Duration tickDuration)
      Obtains a source that returns instants from the specified source truncated to the nearest occurrence of the specified duration.

      This source will only tick as per the specified duration. Thus, if the duration is half a second, the source will return instants truncated to the half second.

      The tick duration must be positive. If it has a part smaller than a whole millisecond, then the whole duration must divide into one second without leaving a remainder. All normal tick durations will match these criteria, including any multiple of hours, minutes, seconds and milliseconds, and sensible nanosecond durations, such as 20ns, 250,000ns and 500,000ns.

      A duration of zero or one nanosecond would have no truncation effect. Passing one of these will return the underlying source.

      Implementations may use a caching strategy for performance reasons. As such, it is possible that the start of the requested duration observed via this source will be later than that observed directly via the underlying source.

      The returned implementation is immutable, thread-safe and Serializable providing that the base source is.

      Parameters:
      baseSource - the base source to base the ticking source on, not null
      tickDuration - the duration of each visible tick, not negative, not null
      Returns:
      a source that ticks in whole units of the duration, not null
      Throws:
      IllegalArgumentException - if the duration is negative, or has a part smaller than a whole millisecond such that the whole duration is not divisible into one second
      ArithmeticException - if the duration is too large to be represented as nanos

    • fixed

      static InstantSource fixed(Instant fixedInstant)
      Obtains a source that always returns the same instant.

      This source simply returns the specified instant. As such, it is not a source that represents the current instant. The main use case for this is in testing, where the fixed source ensures tests are not dependent on the current source.

      The returned implementation is immutable, thread-safe and Serializable.

      Parameters:
      fixedInstant - the instant to use, not null
      Returns:
      a source that always returns the same instant, not null

    • offset

      static InstantSource offset(InstantSource baseSource, Duration offsetDuration)
      Obtains a source that returns instants from the specified source with the specified duration added.

      This source wraps another source, returning instants that are later by the specified duration. If the duration is negative, the instants will be earlier than the current date and time. The main use case for this is to simulate running in the future or in the past.

      A duration of zero would have no offsetting effect. Passing zero will return the underlying source.

      The returned implementation is immutable, thread-safe and Serializable providing that the base source is.

      Parameters:
      baseSource - the base source to add the duration to, not null
      offsetDuration - the duration to add, not null
      Returns:
      a source based on the base source with the duration added, not null

    • instant

      Instant instant()
      Gets the current instant of the source.

      This returns an instant representing the current instant as defined by the source.

      Returns:
      the current instant from this source, not null
      Throws:
      DateTimeException - if the instant cannot be obtained, not thrown by most implementations

    • millis

      default long millis()
      Gets the current millisecond instant of the source.

      This returns the millisecond-based instant, measured from 1970-01-01T00:00Z (UTC). This is equivalent to the definition of System.currentTimeMillis().

      Most applications should avoid this method and use Instant to represent an instant on the time-line rather than a raw millisecond value. This method is provided to allow the use of the source in high performance use cases where the creation of an object would be unacceptable.

      Returns:
      the current millisecond instant from this source, measured from the Java epoch of 1970-01-01T00:00Z (UTC), not null
      Throws:
      DateTimeException - if the instant cannot be obtained, not thrown by most implementations

    • withZone

      default Clock withZone(ZoneId zone)
      Returns a clock with the specified time-zone.

      This returns a Clock, which is an extension of this interface that combines this source and the specified time-zone.

      The returned implementation is immutable, thread-safe and Serializable providing that this source is.

      Parameters:
      zone - the time-zone to use, not null
      Returns:
      a clock based on this source with the specified time-zone, not null