public final class SystemClock extends Object
Three different clocks are available, and they should not be confused:
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
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
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
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
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.
Standard functions like
are always available. These functions use the
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
you must handle
SystemClock.sleep(millis) is a utility function
very similar to
Thread.sleep(millis), but it
InterruptedException. Use this function for delays if
you do not use
Thread.interrupt(), as it will
preserve the interrupted state of the thread.
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).
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
System.currentTimeMillis() (RTC) or
elapsedRealtime() (ELAPSED_REALTIME), and cause an
Intent broadcast when they occur.
|Modifier and Type||Method and Description|
Returns microseconds running in the current thread.
Returns milliseconds running in the current thread.
Returns current wall time in microseconds.
Returns milliseconds since boot, including time spent in sleep.
Returns nanoseconds since boot, including time spent in sleep.
Sets the current wall time, in milliseconds.
Waits a given number of milliseconds (of uptimeMillis) before returning.
Returns milliseconds since boot, not counting time spent in deep sleep.
public static void sleep(long ms)
Thread.sleep(long), but does not throw
Thread.interrupt()events are deferred until the next interruptible operation. Does not return until at least the specified number of milliseconds has elapsed.
ms- to sleep before returning, in milliseconds of uptime.
public static boolean setCurrentTimeMillis(long millis)
public static long uptimeMillis()
public static long elapsedRealtime()
public static long elapsedRealtimeNanos()
public static long currentThreadTimeMillis()
public static long currentThreadTimeMicro()
public static long currentTimeMicro()