This
interface
extends Executor and
ExecutorService to add methods for scheduling
Callable or Runnable tasks for
future execution on a one-time basis or a repeating basis. The
schedule( ) methods schedule a
Callable or a Runnable task for
one-time execution after a specified delay. The delay is specified by
a long plus a TimeUnit. When a
Callable<V> is scheduled, the result is a
ScheduledFuture<V>. This is like a
Future<V> object but also implements the
Delay interface so you can call getdelay(
) to find out how much time remains before execution
begins. If you schedule( ) a
Runnable object, the result is a
ScheduledFuture<?>. Since a
Runnable has no return value, the get(
) method of this ScheduledFuture returns
null, but the cancel( ),
geTDelay( ), and isDone( )
methods remain useful.
ScheduledExecutorService provides two alternatives
for scheduling Runnable tasks for repeated
execution. (See also java.util.Timer, which has
similar methods.) scheduleAtFixedRate( ) begins
the first execution of the Runnable after
initialDelay time units, and begins
subsequent executions at multiples of
period time units after that. This means
that the Runnable runs at a fixed rate, regardless
of how long each execution takes. scheduleWithFixedDelay(
) also begins the first execution after
initialDelay time units. But it waits for
this first execution (and all subsequent executions) to complete
before scheduling the next execution for
delay time units in the future. Both
methods return a ScheduledFuture object that you
can use to cancel( ) the repeated execution of
tasks. If the task is not canceled, the
ScheduledExecutorService runs it repeatedly until
the service is shut down (see ExecutorService) or
the Runnable throws an exception.
public interface ScheduledExecutorService extends ExecutorService {
// Public Instance Methods
<V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit);
ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit);
ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay,
long period, TimeUnit unit);
ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay,
long delay, TimeUnit unit);
}
