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.
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);
}
}
ScheduledFuture<?> schedule(Runnable command,
long delay,
TimeUnit unit) Creates and executes a one-shot action that becomes enabled after the given delay.
command - the task to executedelay - the time from now to delay executionunit - the time unit of the delay parameterget() method will return null upon completionRejectedExecutionException - if the task cannot be scheduled for executionNullPointerException - if command is null<V> ScheduledFuture<V> schedule(Callable<V> callable,
long delay,
TimeUnit unit) Creates and executes a ScheduledFuture that becomes enabled after the given delay.
V - the type of the callable's resultcallable - the function to executedelay - the time from now to delay executionunit - the time unit of the delay parameterRejectedExecutionException - if the task cannot be scheduled for executionNullPointerException - if callable is nullScheduledFuture<?> 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. 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.
command - the task to executeinitialDelay - the time to delay first executionperiod - the period between successive executionsunit - the time unit of the initialDelay and period parametersget() method will throw an exception upon cancellationRejectedExecutionException - if the task cannot be scheduled for executionNullPointerException - if command is nullIllegalArgumentException - if period less than or equal to zeroScheduledFuture<?> 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.
command - the task to executeinitialDelay - the time to delay first executiondelay - the delay between the termination of one execution and the commencement of the nextunit - the time unit of the initialDelay and delay parametersget() method will throw an exception upon cancellationRejectedExecutionException - if the task cannot be scheduled for executionNullPointerException - if command is nullIllegalArgumentException - if delay less than or equal to zero
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