ScheduledExecutorService

public interface ScheduledExecutorService implements ExecutorService
Known Indirect Subclasses

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 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() {
     final Runnable beeper = new Runnable() {
       public void run() { System.out.println("beep"); }
     };
     final ScheduledFuture<?> beeperHandle =
       scheduler.scheduleAtFixedRate(beeper, 10, 10, SECONDS);
     scheduler.schedule(new Runnable() {
       public void run() { beeperHandle.cancel(true); }
     }, 60 * 60, SECONDS);
   }
 }

Public Method Summary

abstract <V> ScheduledFuture<V>
schedule(Callable<V> callable, long delay, TimeUnit unit)
Creates and executes a ScheduledFuture that becomes enabled after the given delay.
abstract ScheduledFuture<?>
schedule(Runnable command, long delay, TimeUnit unit)
Creates and executes a one-shot action that becomes enabled after the given delay.
abstract ScheduledFuture<?>
scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
Creates and executes 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)
Creates and executes 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 Method Summary

Public Methods

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

Creates and executes a ScheduledFuture that becomes enabled after the given delay.

Parameters
callable the function to execute
delay the time from now to delay execution
unit the time unit of the delay parameter
Returns
  • a ScheduledFuture that can be used to extract result or cancel
Throws
RejectedExecutionException if the task cannot be scheduled for execution
NullPointerException if callable is null

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

Creates and executes a one-shot action that becomes enabled after the given delay.

Parameters
command the task to execute
delay the time from now to delay execution
unit the time unit of the delay parameter
Returns
  • 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 is null

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

Creates and executes 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 {@linkplain Future#cancel 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 futur