public
interface
ScheduledExecutorService
implements
ExecutorService
java.util.concurrent.ScheduledExecutorService |
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.
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 methods | |
---|---|
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
|
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 methods | |
---|---|
From
interface
java.util.concurrent.ExecutorService
| |
From
interface
java.util.concurrent.Executor
|
ScheduledFuture<V> schedule (Callable<V> callable, long delay, TimeUnit unit)
Creates and executes a ScheduledFuture 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 is null |
ScheduledFuture<?> schedule (Runnable command, long delay, TimeUnit unit)
Creates and executes a one-shot action 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 is null |
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:
get
on the returned future will
throw ExecutionException
.
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 is null |
IllegalArgumentException |
if period less than or equal to zero |
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.
The sequence of task executions continues indefinitely until one of the following exceptional completions occur:
get
on the returned future will
throw ExecutionException
.
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 is null |
IllegalArgumentException |
if delay less than or equal to zero |