The {@code schedule} methods create tasks with various delays * and return a task object that can be used to cancel or check * execution. The {@code scheduleAtFixedRate} and * {@code scheduleWithFixedDelay} methods create and execute tasks * that run periodically until cancelled. * *
Commands submitted using the {@link Executor#execute(Runnable)} * and {@link ExecutorService} {@code submit} methods are scheduled * with a requested delay of zero. Zero and negative delays (but not * periods) are also allowed in {@code schedule} methods, and are * treated as requests for immediate execution. * *
All {@code 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 {@code date}, you can use: {@code schedule(task, * date.getTime() - System.currentTimeMillis(), * TimeUnit.MILLISECONDS)}. Beware however that expiration of a * relative delay need not coincide with the current {@code 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. * *
{@code
* 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
*/
public interface ScheduledExecutorService extends ExecutorService {
/**
* 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 ScheduledFuture representing pending completion of
* the task and whose {@code get()} method will return
* {@code null} upon completion
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
* @throws NullPointerException if command is null
*/
public ScheduledFuture schedule(Runnable command,
long delay, 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
* @param The sequence of task executions continues indefinitely until * one of the following exceptional completions occur: *
If any execution of this task takes longer than its period, then * subsequent executions may start late, but will not concurrently * execute. * * @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 ScheduledFuture representing pending completion of * the series of repeated tasks. The future's {@link * Future#get() 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 * @throws NullPointerException if command is null * @throws IllegalArgumentException if period less than or equal to zero */ public 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 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: *