Added in API level 1

Summary: Methods | Inherited Methods

ScheduledExecutorService

public interface ScheduledExecutorService
implements ExecutorService

java.util.concurrent.ScheduledExecutorService

Known indirect subclasses ScheduledThreadPoolExecutor ScheduledThreadPoolExecutor A ThreadPoolExecutor that can additionally schedule commands to run after a given delay, or to execute periodically.

---

An 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.

Usage Example

Here is a class with a method that sets up a ScheduledExecutorService to beep every ten seconds for an hour:

 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);
   }
 }

Summary

Public methods
abstract <V> ScheduledFuture<V>	schedule(Callable<V> callable, long delay, TimeUnit unit) Submits a value-returning one-shot task that becomes enabled after the given delay.
abstract ScheduledFuture<?>	schedule(Runnable command, long delay, TimeUnit unit) Submits a one-shot task that becomes enabled after the given delay.
abstract ScheduledFuture<?>	scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit) 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.
abstract ScheduledFuture<?>	scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit) 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.

Inherited methods
From interface java.util.concurrent.ExecutorService abstract boolean awaitTermination(long timeout, TimeUnit unit) Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first. default void close() Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. abstract <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) Executes the given tasks, returning a list of Futures holding their status and results when all complete. abstract <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first. abstract <T> T invokeAny(Collection<? extends Callable<T>> tasks) Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do. abstract <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses. abstract boolean isShutdown() Returns true if this executor has been shut down. abstract boolean isTerminated() Returns true if all tasks have completed following shut down. abstract void shutdown() Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. abstract List<Runnable> shutdownNow() Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. abstract Future<?> submit(Runnable task) Submits a Runnable task for execution and returns a Future representing that task. abstract <T> Future<T> submit(Callable<T> task) Submits a value-returning task for execution and returns a Future representing the pending results of the task. abstract <T> Future<T> submit(Runnable task, T result) Submits a Runnable task for execution and returns a Future representing that task.
From interface java.lang.AutoCloseable abstract void close() Closes this resource, relinquishing any underlying resources.
From interface java.util.concurrent.Executor abstract void execute(Runnable command) Executes the given command at some time in the future.

Public methods

schedule

Added in API level 1

public abstract ScheduledFuture<V> schedule (Callable<V> callable, 
                long delay, 
                TimeUnit unit)

Submits a value-returning one-shot task that becomes enabled after the given delay.

Parameters
callable	Callable: the function to execute
delay	long: the time from now to delay execution
unit	TimeUnit: the time unit of the delay parameter

Returns
ScheduledFuture<V>	a ScheduledFuture that can be used to extract result or cancel

Throws
RejectedExecutionException	if the task cannot be scheduled for execution
NullPointerException	if callable or unit is null

schedule

Added in API level 1

public abstract ScheduledFuture<?> schedule (Runnable command, 
                long delay, 
                TimeUnit unit)

Submits a one-shot task that becomes enabled after the given delay.

Parameters
command	Runnable: the task to execute
delay	long: the time from now to delay execution
unit	TimeUnit: the time unit of the delay parameter

Returns
ScheduledFuture<?>	a ScheduledFuture representing pending completion of the task and whose get() method will return null upon completion

Throws
RejectedExecutionException	if the task cannot be scheduled for execution
NullPointerException	if command or unit is null

scheduleAtFixedRate

Added in API level 1

public abstract ScheduledFuture<?> scheduleAtFixedRate (Runnable command, 
                long initialDelay, 
                long period, 
                TimeUnit unit)

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.

The sequence of task executions continues indefinitely until one of the following exceptional completions occur:

• The task is explicitly cancelled via the returned future.
• The executor terminates, also resulting in task cancellation.
• An execution of the task throws an exception. In this case calling get on the returned future will throw ExecutionException, holding the exception as its cause.

Subsequent executions are suppressed. Subsequent calls to 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.

Parameters
command	Runnable: the task to execute
initialDelay	long: the time to delay first execution
period	long: the period between successive executions
unit	TimeUnit: the time unit of the initialDelay and period parameters

Returns
ScheduledFuture<?>	a ScheduledFuture representing pending completion of the series of repeated tasks. The future's get() method will never return normally, and will throw an exception upon task cancellation or abnormal termination of a task execution.

Throws
RejectedExecutionException	if the task cannot be scheduled for execution
NullPointerException	if command or unit is null
IllegalArgumentException	if period less than or equal to zero

scheduleWithFixedDelay

Added in API level 1

public abstract ScheduledFuture<?> scheduleWithFixedDelay (Runnable command, 
                long initialDelay, 
                long delay, 
                TimeUnit unit)

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.

The sequence of task executions continues indefinitely until one of the following exceptional completions occur:

• The task is explicitly cancelled via the returned future.
• The executor terminates, also resulting in task cancellation.
• An execution of the task throws an exception. In this case calling get on the returned future will throw ExecutionException, holding the exception as its cause.

Subsequent executions are suppressed. Subsequent calls to isDone() on the returned future will return true.

Parameters
command	Runnable: the task to execute
initialDelay	long: the time to delay first execution
delay	long: the delay between the termination of one execution and the commencement of the next
unit	TimeUnit: the time unit of the initialDelay and delay parameters

Returns
ScheduledFuture<?>	a ScheduledFuture representing pending completion of the series of repeated tasks. The future's get() method will never return normally, and will throw an exception upon task cancellation or abnormal termination of a task execution.

Throws
RejectedExecutionException	if the task cannot be scheduled for execution
NullPointerException	if command or unit is null
IllegalArgumentException	if delay less than or equal to zero