Added in API level 1

SystemClock


class SystemClock
kotlin.Any
   ↳ android.os.SystemClock

Core timekeeping facilities.

Three different clocks are available, and they should not be confused:

  • System.currentTimeMillis() is the standard "wall" clock (time and date) expressing milliseconds since the epoch. The wall clock can be set by the user or the phone network (see setCurrentTimeMillis), so the time may jump backwards or forwards unpredictably. This clock should only be used when correspondence with real-world dates and times is important, such as in a calendar or alarm clock application. Interval or elapsed time measurements should use a different clock. If you are using System.currentTimeMillis(), consider listening to the ACTION_TIME_TICK, ACTION_TIME_CHANGED and ACTION_TIMEZONE_CHANGED Intent broadcasts to find out when the time changes.

  • uptimeMillis is counted in milliseconds since the system was booted. This clock stops when the system enters deep sleep (CPU off, display dark, device waiting for external input), but is not affected by clock scaling, idle, or other power saving mechanisms. This is the basis for most interval timing such as Thread.sleep(millls), Object.wait(millis), and System.nanoTime(). This clock is guaranteed to be monotonic, and is suitable for interval timing when the interval does not span device sleep. Most methods that accept a timestamp value currently expect the uptimeMillis clock.

  • elapsedRealtime and elapsedRealtimeNanos return the time since the system was booted, and include deep sleep. This clock is guaranteed to be monotonic, and continues to tick even when the CPU is in power saving modes, so is the recommend basis for general purpose interval timing.

There are several mechanisms for controlling the timing of events:

Summary

Public methods
static Clock

Returns a Clock that starts at January 1, 1970 00:00:00.

static Clock

Returns a Clock that starts at January 1, 1970 00:00:00.

static Long

Returns milliseconds running in the current thread.

static Long

Returns milliseconds since boot, including time spent in sleep.

static Long

Returns nanoseconds since boot, including time spent in sleep.

static Boolean

Sets the current wall time, in milliseconds.

static Unit
sleep(ms: Long)

Waits a given number of milliseconds (of uptimeMillis) before returning.

static Long

Returns milliseconds since boot, not counting time spent in deep sleep.

static Long

Returns nanoseconds since boot, not counting time spent in deep sleep.

Public methods

currentGnssTimeClock

Added in API level 29
static fun currentGnssTimeClock(): Clock

Returns a Clock that starts at January 1, 1970 00:00:00.0 UTC, synchronized using the device's location provider.

Return
Clock This value cannot be null.
Exceptions
java.time.DateTimeException when the location provider has not had a location fix since boot.

currentNetworkTimeClock

Added in API level 33
static fun currentNetworkTimeClock(): Clock

Returns a Clock that starts at January 1, 1970 00:00:00.0 UTC, synchronized using a remote network source outside the device.

While the time returned by System#currentTimeMillis() can be adjusted by the user, the time returned by this method cannot be adjusted by the user.

This performs no blocking network operations and returns values based on a recent successful synchronization event; it will either return a valid time or throw.

Note that synchronization may occur using an insecure network protocol, so the returned time should not be used for security purposes. The device may resynchronize with the same or different network source at any time. Due to network delays, variations between servers, or local (client side) clock drift, the accuracy of the returned times cannot be guaranteed. In extreme cases, consecutive calls to java.time.Clock#millis() on the returned Clockcould return times that are out of order.

Return
Clock This value cannot be null.
Exceptions
java.time.DateTimeException when no network time can be provided.

currentThreadTimeMillis

Added in API level 1
static fun currentThreadTimeMillis(): Long

Returns milliseconds running in the current thread.

Return
Long elapsed milliseconds in the thread

elapsedRealtime

Added in API level 1
static fun elapsedRealtime(): Long

Returns milliseconds since boot, including time spent in sleep.

Return
Long elapsed milliseconds since boot.

elapsedRealtimeNanos

Added in API level 17
static fun elapsedRealtimeNanos(): Long

Returns nanoseconds since boot, including time spent in sleep.

Return
Long elapsed nanoseconds since boot.

setCurrentTimeMillis

Added in API level 1
static fun setCurrentTimeMillis(millis: Long): Boolean

Sets the current wall time, in milliseconds. Requires the calling process to have appropriate permissions.

Return
Boolean if the clock was successfully set to the specified time.

sleep

Added in API level 1
static fun sleep(ms: Long): Unit

Waits a given number of milliseconds (of uptimeMillis) before returning. Similar to java.lang.Thread#sleep(long), but does not throw InterruptedException; Thread#interrupt() events are deferred until the next interruptible operation. Does not return until at least the specified number of milliseconds has elapsed.

Parameters
ms Long: to sleep before returning, in milliseconds of uptime.

uptimeMillis

Added in API level 1
static fun uptimeMillis(): Long

Returns milliseconds since boot, not counting time spent in deep sleep.

Return
Long milliseconds of non-sleep uptime since boot.

uptimeNanos

Added in API level 35
static fun uptimeNanos(): Long

Returns nanoseconds since boot, not counting time spent in deep sleep.

Return
Long nanoseconds of non-sleep uptime since boot.