Added in API level 1

Summary: Methods | Inherited Methods

SystemClock

Kotlin |Java

public final class SystemClock
extends Object

java.lang.Object
↳	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(long)), 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:

Standard functions like Thread.sleep(millis) and Object.wait(millis) are always available. These functions use the uptimeMillis() clock; if the device enters sleep, the remainder of the time will be postponed until the device wakes up. These synchronous functions may be interrupted with Thread.interrupt(), and you must handle InterruptedException.
SystemClock.sleep(millis) is a utility function very similar to Thread.sleep(millis), but it ignores InterruptedException. Use this function for delays if you do not use Thread.interrupt(), as it will preserve the interrupted state of the thread.
The Handler class can schedule asynchronous callbacks at an absolute or relative time. Handler objects also use the uptimeMillis() clock, and require an event loop (normally present in any GUI application).
The AlarmManager can trigger one-time or recurring events which occur even when the device is in deep sleep or your application is not running. Events may be scheduled with your choice of System.currentTimeMillis() (RTC) or elapsedRealtime() (ELAPSED_REALTIME), and cause an Intent broadcast when they occur.

Summary

Public methods
`static Clock`	`currentGnssTimeClock()` Returns a `Clock` that starts at January 1, 1970 00:00:00.0 UTC, synchronized using the device's location provider.
`static Clock`	`currentNetworkTimeClock()` Returns a `Clock` that starts at January 1, 1970 00:00:00.0 UTC, synchronized using a remote network source outside the device.
`static long`	`currentThreadTimeMillis()` Returns milliseconds running in the current thread.
`static long`	`elapsedRealtime()` Returns milliseconds since boot, including time spent in sleep.
`static long`	`elapsedRealtimeNanos()` Returns nanoseconds since boot, including time spent in sleep.
`static boolean`	`setCurrentTimeMillis(long millis)` Sets the current wall time, in milliseconds.
`static void`	`sleep(long ms)` Waits a given number of milliseconds (of uptimeMillis) before returning.
`static long`	`uptimeMillis()` Returns milliseconds since boot, not counting time spent in deep sleep.
`static long`	`uptimeNanos()` Returns nanoseconds since boot, not counting time spent in deep sleep.

Inherited methods

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

Public methods

currentGnssTimeClock

Added in API level 29

public static Clock currentGnssTimeClock ()

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

Returns
`Clock`	This value cannot be `null`.

Throws
`DateTimeException`	when the location provider has not had a location fix since boot.

currentNetworkTimeClock

Added in API level 33

public static Clock currentNetworkTimeClock ()

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 Clock.millis() on the returned Clockcould return times that are out of order.

Returns
`Clock`	This value cannot be `null`.

Throws
`DateTimeException`	when no network time can be provided.

currentThreadTimeMillis

Added in API level 1

public static long currentThreadTimeMillis ()

Returns milliseconds running in the current thread.

Returns
`long`	elapsed milliseconds in the thread

elapsedRealtime

Added in API level 1

public static long elapsedRealtime ()

Returns milliseconds since boot, including time spent in sleep.

Returns
`long`	elapsed milliseconds since boot.

elapsedRealtimeNanos

Added in API level 17

public static long elapsedRealtimeNanos ()

Returns nanoseconds since boot, including time spent in sleep.

Returns
`long`	elapsed nanoseconds since boot.

setCurrentTimeMillis

Added in API level 1

public static boolean setCurrentTimeMillis (long millis)

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

Parameters
`millis`	`long`

Returns
`boolean`	if the clock was successfully set to the specified time.

sleep

Added in API level 1

public static void sleep (long ms)

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

public static long uptimeMillis ()

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

Returns
`long`	milliseconds of non-sleep uptime since boot.

uptimeNanos

Added in API level 35

public static long uptimeNanos ()

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

Returns
`long`	nanoseconds of non-sleep uptime since boot.