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ScheduledExecutorService.javaAPI DocAndroid 1.5 API6537Wed May 06 22:41:02 BST 2009java.util.concurrent

ScheduledExecutorService

public interface ScheduledExecutorService implements ExecutorService
An {@link 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 {@link Executor#execute} and {@link 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 {@link java.util.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 {@link 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
author
Doug Lea

Fields Summary
Constructors Summary
Methods Summary
public java.util.concurrent.ScheduledFutureschedule(java.lang.Runnable command, long delay, java.util.concurrent.TimeUnit unit)
Creates and executes a one-shot action that becomes enabled after the given delay.

param
command the task to execute.
param
delay the time from now to delay execution.
param
unit the time unit of the delay parameter.
return
a Future representing pending completion of the task, and whose get() method will return null upon completion.
throws
RejectedExecutionException if task cannot be scheduled for execution.
throws
NullPointerException if command is null

public java.util.concurrent.ScheduledFutureschedule(java.util.concurrent.Callable callable, long delay, java.util.concurrent.TimeUnit unit)
Creates and executes a ScheduledFuture that becomes enabled after the given delay.

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

public java.util.concurrent.ScheduledFuturescheduleAtFixedRate(java.lang.Runnable command, long initialDelay, long period, java.util.concurrent.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.

param
command the task to execute.
param
initialDelay the time to delay first execution.
param
period the period between successive executions.
param
unit the time unit of the initialDelay and period parameters
return
a Future representing pending completion of the task, and whose get() method will throw an exception upon cancellation.
throws
RejectedExecutionException if task cannot be scheduled for execution.
throws
NullPointerException if command is null
throws
IllegalArgumentException if period less than or equal to zero.

public java.util.concurrent.ScheduledFuturescheduleWithFixedDelay(java.lang.Runnable command, long initialDelay, long delay, java.util.concurrent.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.

param
command the task to execute.
param
initialDelay the time to delay first execution.
param
delay the delay between the termination of one execution and the commencement of the next.
param
unit the time unit of the initialDelay and delay parameters
return
a Future representing pending completion of the task, and whose get() method will throw an exception upon cancellation.
throws
RejectedExecutionException if task cannot be scheduled for execution.
throws
NullPointerException if command is null
throws
IllegalArgumentException if delay less than or equal to zero.