Interface ScheduledExecutorService
- All Superinterfaces:
-
Executor
,ExecutorService
- All Known Implementing Classes:
ScheduledThreadPoolExecutor
public interface ScheduledExecutorService extends ExecutorService
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); } }
- Since:
- 1.5
Method Summary
Modifier and Type | Method | Description |
---|---|---|
ScheduledFuture<?> | schedule(Runnable command,
long delay,
TimeUnit unit) | Submits a one-shot task that becomes enabled after the given delay. |
<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. |
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 |
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. |
Methods declared in interface java.util.concurrent.Executor
execute
Methods declared in interface java.util.concurrent.ExecutorService
awaitTermination, invokeAll, invokeAll, invokeAny, invokeAny, isShutdown, isTerminated, shutdown, shutdownNow, submit, submit, submit
Method Detail
schedule
ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)
Submits a one-shot task 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 returnnull
upon completion - Throws:
-
RejectedExecutionException
- if the task cannot be scheduled for execution -
NullPointerException
- if command or unit is null
schedule
<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.
- Type Parameters:
-
V
- the type of the callable's result - 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 or unit is null
scheduleAtFixedRate
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 throwExecutionException
, 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.
- Parameters:
-
command
- the task to execute -
initialDelay
- the time to delay first execution -
period
- the period between successive executions -
unit
- the time unit of the initialDelay and period parameters - Returns:
- 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
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 throwExecutionException
, holding the exception as its cause.
isDone()
on the returned future will return true
.- Parameters:
-
command
- the task to execute -
initialDelay
- the time to delay first execution -
delay
- the delay between the termination of one execution and the commencement of the next -
unit
- the time unit of the initialDelay and delay parameters - Returns:
- 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