AutoCloseable
, Executor
, ExecutorService
ScheduledThreadPoolExecutor
public interface ScheduledExecutorService extends ExecutorService
ExecutorService
that can schedule commands to run after a given delay, or to execute periodically. The schedule
methods create tasks with various delays and return a task object that can be used to cancel or check execution. The scheduleAtFixedRate
and scheduleWithFixedDelay
methods create and execute tasks that run periodically until cancelled.
Commands submitted using the Executor.execute(Runnable)
and ExecutorService
submit
methods are scheduled with a requested delay of zero. Zero and negative delays (but not periods) are also allowed in schedule
methods, and are treated as requests for immediate execution.
All schedule
methods accept relative delays and periods as arguments, not absolute times or dates. It is a simple matter to transform an absolute time represented as a Date
to the required form. For example, to schedule at a certain future date
, you can use: schedule(task,
date.getTime() - System.currentTimeMillis(),
TimeUnit.MILLISECONDS)
. Beware however that expiration of a relative delay need not coincide with the current Date
at which the task is enabled due to network time synchronization protocols, clock drift, or other factors.
The Executors
class provides convenient factory methods for the ScheduledExecutorService implementations provided in this package.
import static java.util.concurrent.TimeUnit.*;
class BeeperControl {
private final ScheduledExecutorService scheduler =
Executors.newScheduledThreadPool(1);
public void beepForAnHour() {
Runnable beeper = () -> System.out.println("beep");
ScheduledFuture<?> beeperHandle =
scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
Runnable canceller = () -> beeperHandle.cancel(false);
scheduler.schedule(canceller, 1, HOURS);
}
}
Modifier and Type | Method | Description |
---|---|---|
ScheduledFuture |
schedule |
Submits a one-shot task that becomes enabled after the given delay. |
<V> ScheduledFuture |
schedule |
Submits a value-returning one-shot task that becomes enabled after the given delay. |
ScheduledFuture |
scheduleAtFixedRate |
Submits a periodic action that becomes enabled first after the given initial delay, and subsequently with the given period; that is, executions will commence after initialDelay , then initialDelay + period , then initialDelay + 2 * period , and so on. |
ScheduledFuture |
scheduleWithFixedDelay |
Submits a periodic action that becomes enabled first after the given initial delay, and subsequently with the given delay between the termination of one execution and the commencement of the next. |
awaitTermination, close, invokeAll, invokeAll, invokeAny, invokeAny, isShutdown, isTerminated, shutdown, shutdownNow, submit, submit, submit
ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)
command
- the task to executedelay
- the time from now to delay executionunit
- the time unit of the delay parameterget()
method will return null
upon completionRejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if command or unit is null<V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)
V
- the type of the callable's resultcallable
- the function to executedelay
- the time from now to delay executionunit
- the time unit of the delay parameterRejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if callable or unit is nullScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
initialDelay
, then initialDelay + period
, then initialDelay + 2 * period
, and so on. The sequence of task executions continues indefinitely until one of the following exceptional completions occur:
get
on the returned future will throw ExecutionException
, holding the exception as its cause. isDone()
on the returned future will return true
. If any execution of this task takes longer than its period, then subsequent executions may start late, but will not concurrently execute.
command
- the task to executeinitialDelay
- the time to delay first executionperiod
- the period between successive executionsunit
- the time unit of the initialDelay and period parametersget()
method will never return normally, and will throw an exception upon task cancellation or abnormal termination of a task execution.RejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if command or unit is nullIllegalArgumentException
- if period less than or equal to zeroScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)
The sequence of task executions continues indefinitely until one of the following exceptional completions occur:
get
on the returned future will throw ExecutionException
, holding the exception as its cause. isDone()
on the returned future will return true
.command
- the task to executeinitialDelay
- the time to delay first executiondelay
- the delay between the termination of one execution and the commencement of the nextunit
- the time unit of the initialDelay and delay parametersget()
method will never return normally, and will throw an exception upon task cancellation or abnormal termination of a task execution.RejectedExecutionException
- if the task cannot be scheduled for executionNullPointerException
- if command or unit is nullIllegalArgumentException
- if delay less than or equal to zero
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/ScheduledExecutorService.html