ScheduledExecutorService (Java Platform SE 6) (original) (raw)

java.util.concurrent

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 andscheduleWithFixedDelay methods create and execute tasks that run periodically until cancelled.

Commands submitted using the Executor.execute(java.lang.Runnable) andExecutorService 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);
}

}

Since:

1.5

schedule

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 returnnull upon completion

Throws:

[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent") - if the task cannot be scheduled for execution

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if command is null

schedule

ScheduledFuture schedule(Callable 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](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent") - if the task cannot be scheduled for execution

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if callable is null

scheduleAtFixedRate

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 afterinitialDelay then initialDelay+period, theninitialDelay + 2 * period, and so on. If any execution of the task encounters an exception, subsequent executions are suppressed. Otherwise, the task will only terminate via cancellation or termination of the executor. 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 task, and whose get() method will throw an exception upon cancellation

Throws:

[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent") - if the task cannot be scheduled for execution

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if command is null

[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang") - if period less than or equal to zero

scheduleWithFixedDelay

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. If any execution of the task encounters an exception, subsequent executions are suppressed. Otherwise, the task will only terminate via cancellation or termination of the executor.

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 task, and whose get() method will throw an exception upon cancellation

Throws:

[RejectedExecutionException](../../../java/util/concurrent/RejectedExecutionException.html "class in java.util.concurrent") - if the task cannot be scheduled for execution

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if command is null

[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang") - if delay less than or equal to zero

Submit a bug or feature
For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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