Added in API level 1

Summary: Ctors | Methods | Protected Methods | Inherited Methods

ScheduledThreadPoolExecutor

public class ScheduledThreadPoolExecutor
extends ThreadPoolExecutor implements ScheduledExecutorService

java.lang.Object
↳	java.util.concurrent.AbstractExecutorService
	↳	java.util.concurrent.ThreadPoolExecutor
		↳	java.util.concurrent.ScheduledThreadPoolExecutor

A ThreadPoolExecutor that can additionally schedule commands to run after a given delay, or to execute periodically. This class is preferable to Timer when multiple worker threads are needed, or when the additional flexibility or capabilities of ThreadPoolExecutor (which this class extends) are required.

Delayed tasks execute no sooner than they are enabled, but without any real-time guarantees about when, after they are enabled, they will commence. Tasks scheduled for exactly the same execution time are enabled in first-in-first-out (FIFO) order of submission.

When a submitted task is cancelled before it is run, execution is suppressed. By default, such a cancelled task is not automatically removed from the work queue until its delay elapses. While this enables further inspection and monitoring, it may also cause unbounded retention of cancelled tasks.

Successive executions of a periodic task scheduled via scheduleAtFixedRate or scheduleWithFixedDelay do not overlap. While different executions may be performed by different threads, the effects of prior executions happen-before those of subsequent ones.

While this class inherits from ThreadPoolExecutor, a few of the inherited tuning methods are not useful for it. In particular, because it acts as a fixed-sized pool using corePoolSize threads and an unbounded queue, adjustments to maximumPoolSize have no useful effect. Additionally, it is almost never a good idea to set corePoolSize to zero or use allowCoreThreadTimeOut because this may leave the pool without threads to handle tasks once they become eligible to run.

As with ThreadPoolExecutor, if not otherwise specified, this class uses Executors.defaultThreadFactory as the default thread factory, and ThreadPoolExecutor.AbortPolicy as the default rejected execution handler.

Extension notes: This class overrides the execute and submit methods to generate internal ScheduledFuture objects to control per-task delays and scheduling. To preserve functionality, any further overrides of these methods in subclasses must invoke superclass versions, which effectively disables additional task customization. However, this class provides alternative protected extension method decorateTask (one version each for Runnable and Callable) that can be used to customize the concrete task types used to execute commands entered via execute, submit, schedule, scheduleAtFixedRate, and scheduleWithFixedDelay. By default, a ScheduledThreadPoolExecutor uses a task type extending FutureTask. However, this may be modified or replaced using subclasses of the form:

 public class CustomScheduledExecutor extends ScheduledThreadPoolExecutor {

   static class CustomTask<V> implements RunnableScheduledFuture<V> { ... }

   protected <V> RunnableScheduledFuture<V> decorateTask(
                Runnable r, RunnableScheduledFuture<V> task) {
       return new CustomTask<V>(r, task);
   }

   protected <V> RunnableScheduledFuture<V> decorateTask(
                Callable<V> c, RunnableScheduledFuture<V> task) {
       return new CustomTask<V>(c, task);
   }
   // ... add constructors, etc.
 }

Summary

Public constructors
`ScheduledThreadPoolExecutor(int corePoolSize)` Creates a new `ScheduledThreadPoolExecutor` with the given core pool size.
`ScheduledThreadPoolExecutor(int corePoolSize, RejectedExecutionHandler handler)` Creates a new `ScheduledThreadPoolExecutor` with the given initial parameters.
`ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory)` Creates a new `ScheduledThreadPoolExecutor` with the given initial parameters.
`ScheduledThreadPoolExecutor(int corePoolSize, ThreadFactory threadFactory, RejectedExecutionHandler handler)` Creates a new `ScheduledThreadPoolExecutor` with the given initial parameters.

Public methods
`void`	`execute(Runnable command)` Executes `command` with zero required delay.
`boolean`	`getContinueExistingPeriodicTasksAfterShutdownPolicy()` Gets the policy on whether to continue executing existing periodic tasks even when this executor has been `shutdown`.
`boolean`	`getExecuteExistingDelayedTasksAfterShutdownPolicy()` Gets the policy on whether to execute existing delayed tasks even when this executor has been `shutdown`.
`BlockingQueue<Runnable>`	`getQueue()` Returns the task queue used by this executor.
`boolean`	`getRemoveOnCancelPolicy()` Gets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation.
`<V> ScheduledFuture<V>`	`schedule(Callable<V> callable, long delay, TimeUnit unit)` Submits a value-returning one-shot task that becomes enabled after the given delay.
`ScheduledFuture<?>`	`schedule(Runnable command, long delay, TimeUnit unit)` Submits a one-shot task that becomes enabled after the given delay.
`ScheduledFuture<?>`	`scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)` Submits 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.
`ScheduledFuture<?>`	`scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)` Submits 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.
`void`	`setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean value)` Sets the policy on whether to continue executing existing periodic tasks even when this executor has been `shutdown`.
`void`	`setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean value)` Sets the policy on whether to execute existing delayed tasks even when this executor has been `shutdown`.
`void`	`setRemoveOnCancelPolicy(boolean value)` Sets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation.
`void`	`shutdown()` Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
`List<Runnable>`	`shutdownNow()` Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.
`Future<?>`	`submit(Runnable task)` Submits a Runnable task for execution and returns a Future representing that task.
`<T> Future<T>`	`submit(Callable<T> task)` Submits a value-returning task for execution and returns a Future representing the pending results of the task.
`<T> Future<T>`	`submit(Runnable task, T result)` Submits a Runnable task for execution and returns a Future representing that task.

Protected methods
`<V> RunnableScheduledFuture<V>`	`decorateTask(Runnable runnable, RunnableScheduledFuture<V> task)` Modifies or replaces the task used to execute a runnable.
`<V> RunnableScheduledFuture<V>`	`decorateTask(Callable<V> callable, RunnableScheduledFuture<V> task)` Modifies or replaces the task used to execute a callable.

Inherited methods

From class


        
          java.util.concurrent.ThreadPoolExecutor

`void`	`afterExecute(Runnable r, Throwable t)` Method invoked upon completion of execution of the given Runnable.
`void`	`allowCoreThreadTimeOut(boolean value)` Sets the policy governing whether core threads may time out and terminate if no tasks arrive within the keep-alive time, being replaced if needed when new tasks arrive.
`boolean`	`allowsCoreThreadTimeOut()` Returns true if this pool allows core threads to time out and terminate if no tasks arrive within the keepAlive time, being replaced if needed when new tasks arrive.
`boolean`	`awaitTermination(long timeout, TimeUnit unit)`
`void`	`beforeExecute(Thread t, Runnable r)` Method invoked prior to executing the given Runnable in the given thread.
`void`	`execute(Runnable command)` Executes the given task sometime in the future.
`void`	`finalize()` This method is deprecated. Subclass is not recommended to override finalize(). If it must, please always invoke super.finalize().
`int`	`getActiveCount()` Returns the approximate number of threads that are actively executing tasks.
`long`	`getCompletedTaskCount()` Returns the approximate total number of tasks that have completed execution.
`int`	`getCorePoolSize()` Returns the core number of threads.
`long`	`getKeepAliveTime(TimeUnit unit)` Returns the thread keep-alive time, which is the amount of time that threads may remain idle before being terminated.
`int`	`getLargestPoolSize()` Returns the largest number of threads that have ever simultaneously been in the pool.
`int`	`getMaximumPoolSize()` Returns the maximum allowed number of threads.
`int`	`getPoolSize()` Returns the current number of threads in the pool.
`BlockingQueue<Runnable>`	`getQueue()` Returns the task queue used by this executor.
`RejectedExecutionHandler`	`getRejectedExecutionHandler()` Returns the current handler for unexecutable tasks.
`long`	`getTaskCount()` Returns the approximate total number of tasks that have ever been scheduled for execution.
`ThreadFactory`	`getThreadFactory()` Returns the thread factory used to create new threads.
`boolean`	`isShutdown()`
`boolean`	`isTerminated()`
`boolean`	`isTerminating()` Returns true if this executor is in the process of terminating after `shutdown()` or `shutdownNow()` but has not completely terminated.
`int`	`prestartAllCoreThreads()` Starts all core threads, causing them to idly wait for work.
`boolean`	`prestartCoreThread()` Starts a core thread, causing it to idly wait for work.
`void`	`purge()` Tries to remove from the work queue all `Future` tasks that have been cancelled.
`boolean`	`remove(Runnable task)` Removes this task from the executor's internal queue if it is present, thus causing it not to be run if it has not already started.
`void`	`setCorePoolSize(int corePoolSize)` Sets the core number of threads.
`void`	`setKeepAliveTime(long time, TimeUnit unit)` Sets the thread keep-alive time, which is the amount of time that threads may remain idle before being terminated.
`void`	`setMaximumPoolSize(int maximumPoolSize)` Sets the maximum allowed number of threads.
`void`	`setRejectedExecutionHandler(RejectedExecutionHandler handler)` Sets a new handler for unexecutable tasks.
`void`	`setThreadFactory(ThreadFactory threadFactory)` Sets the thread factory used to create new threads.
`void`	`shutdown()` Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
`List<Runnable>`	`shutdownNow()` Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.
`void`	`terminated()` Method invoked when the Executor has terminated.
`String`	`toString()` Returns a string identifying this pool, as well as its state, including indications of run state and estimated worker and task counts.

From class


        
          java.util.concurrent.AbstractExecutorService

`<T> List<Future<T>>`	`invokeAll(Collection<? extends Callable<T>> tasks)` Executes the given tasks, returning a list of Futures holding their status and results when all complete.
`<T> List<Future<T>>`	`invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)` Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first.
`<T> T`	`invokeAny(Collection<? extends Callable<T>> tasks)` Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do.
`<T> T`	`invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)` Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses.
`<T> RunnableFuture<T>`	`newTaskFor(Runnable runnable, T value)` Returns a `RunnableFuture` for the given runnable and default value.
`<T> RunnableFuture<T>`	`newTaskFor(Callable<T> callable)` Returns a `RunnableFuture` for the given callable task.
`<T> Future<T>`	`submit(Callable<T> task)` Submits a value-returning task for execution and returns a Future representing the pending results of the task.
`<T> Future<T>`	`submit(Runnable task, T result)` Submits a Runnable task for execution and returns a Future representing that task.
`Future<?>`	`submit(Runnable task)` Submits a Runnable task for execution and returns a Future representing that task.

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

From interface


        
          java.util.concurrent.ExecutorService

`abstract boolean`	`awaitTermination(long timeout, TimeUnit unit)` Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.
`default void`	`close()` Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
`abstract <T> List<Future<T>>`	`invokeAll(Collection<? extends Callable<T>> tasks)` Executes the given tasks, returning a list of Futures holding their status and results when all complete.
`abstract <T> List<Future<T>>`	`invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)` Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first.
`abstract <T> T`	`invokeAny(Collection<? extends Callable<T>> tasks)` Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do.
`abstract <T> T`	`invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)` Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses.
`abstract boolean`	`isShutdown()` Returns `true` if this executor has been shut down.
`abstract boolean`	`isTerminated()` Returns `true` if all tasks have completed following shut down.
`abstract void`	`shutdown()` Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted.
`abstract List<Runnable>`	`shutdownNow()` Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.
`abstract Future<?>`	`submit(Runnable task)` Submits a Runnable task for execution and returns a Future representing that task.
`abstract <T> Future<T>`	`submit(Callable<T> task)` Submits a value-returning task for execution and returns a Future representing the pending results of the task.
`abstract <T> Future<T>`	`submit(Runnable task, T result)` Submits a Runnable task for execution and returns a Future representing that task.

From interface


        
          java.util.concurrent.ScheduledExecutorService

`abstract <V> ScheduledFuture<V>`	`schedule(Callable<V> callable, long delay, TimeUnit unit)` Submits a value-returning one-shot task that becomes enabled after the given delay.
`abstract ScheduledFuture<?>`	`schedule(Runnable command, long delay, TimeUnit unit)` Submits a one-shot task that becomes enabled after the given delay.
`abstract ScheduledFuture<?>`	`scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)` Submits 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.
`abstract ScheduledFuture<?>`	`scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)` Submits 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.

From interface


        
          java.lang.AutoCloseable


      close()

Closes this resource, relinquishing any underlying resources.

From interface


        
          java.util.concurrent.Executor


      execute(Runnable command)

Executes the given command at some time in the future.

Public constructors

ScheduledThreadPoolExecutor

Added in API level 1

public ScheduledThreadPoolExecutor (int corePoolSize)

Creates a new ScheduledThreadPoolExecutor with the given core pool size.

Parameters
`corePoolSize`	`int`: the number of threads to keep in the pool, even if they are idle, unless `allowCoreThreadTimeOut` is set

Throws
`IllegalArgumentException`	if `corePoolSize < 0`

ScheduledThreadPoolExecutor

Added in API level 1

public ScheduledThreadPoolExecutor (int corePoolSize, 
                RejectedExecutionHandler handler)

Creates a new ScheduledThreadPoolExecutor with the given initial parameters.

Parameters
`corePoolSize`	`int`: the number of threads to keep in the pool, even if they are idle, unless `allowCoreThreadTimeOut` is set
`handler`	`RejectedExecutionHandler`: the handler to use when execution is blocked because the thread bounds and queue capacities are reached

Throws
`IllegalArgumentException`	if `corePoolSize < 0`
`NullPointerException`	if `handler` is null

ScheduledThreadPoolExecutor

Added in API level 1

public ScheduledThreadPoolExecutor (int corePoolSize, 
                ThreadFactory threadFactory)

Creates a new ScheduledThreadPoolExecutor with the given initial parameters.

Parameters
`corePoolSize`	`int`: the number of threads to keep in the pool, even if they are idle, unless `allowCoreThreadTimeOut` is set
`threadFactory`	`ThreadFactory`: the factory to use when the executor creates a new thread

Throws
`IllegalArgumentException`	if `corePoolSize < 0`
`NullPointerException`	if `threadFactory` is null

ScheduledThreadPoolExecutor

Added in API level 1

public ScheduledThreadPoolExecutor (int corePoolSize, 
                ThreadFactory threadFactory, 
                RejectedExecutionHandler handler)

Creates a new ScheduledThreadPoolExecutor with the given initial parameters.

Parameters
`corePoolSize`	`int`: the number of threads to keep in the pool, even if they are idle, unless `allowCoreThreadTimeOut` is set
`threadFactory`	`ThreadFactory`: the factory to use when the executor creates a new thread
`handler`	`RejectedExecutionHandler`: the handler to use when execution is blocked because the thread bounds and queue capacities are reached

Throws
`IllegalArgumentException`	if `corePoolSize < 0`
`NullPointerException`	if `threadFactory` or `handler` is null

Public methods

execute

Added in API level 1

public void execute (Runnable command)

Executes command with zero required delay. This has effect equivalent to schedule(command, 0, anyUnit). Note that inspections of the queue and of the list returned by shutdownNow will access the zero-delayed ScheduledFuture, not the command itself.

A consequence of the use of ScheduledFuture objects is that afterExecute is always called with a null second Throwable argument, even if the command terminated abruptly. Instead, the Throwable thrown by such a task can be obtained via Future.get.

Parameters
`command`	`Runnable`: the task to execute

Throws
`RejectedExecutionException`	at discretion of `RejectedExecutionHandler`, if the task cannot be accepted for execution because the executor has been shut down
`NullPointerException`

getContinueExistingPeriodicTasksAfterShutdownPolicy

Added in API level 1

public boolean getContinueExistingPeriodicTasksAfterShutdownPolicy ()

Gets the policy on whether to continue executing existing periodic tasks even when this executor has been shutdown. In this case, executions will continue until shutdownNow or the policy is set to false when already shutdown. This value is by default false.

Returns
`boolean`	`true` if will continue after shutdown

See also:

setContinueExistingPeriodicTasksAfterShutdownPolicy(boolean)

getExecuteExistingDelayedTasksAfterShutdownPolicy

Added in API level 1

public boolean getExecuteExistingDelayedTasksAfterShutdownPolicy ()

Gets the policy on whether to execute existing delayed tasks even when this executor has been shutdown. In this case, these tasks will only terminate upon shutdownNow, or after setting the policy to false when already shutdown. This value is by default true.

Returns
`boolean`	`true` if will execute after shutdown

See also:

setExecuteExistingDelayedTasksAfterShutdownPolicy(boolean)

getQueue

Added in API level 1

public BlockingQueue<Runnable> getQueue ()

Returns the task queue used by this executor. Access to the task queue is intended primarily for debugging and monitoring. This queue may be in active use. Retrieving the task queue does not prevent queued tasks from executing.

Each element of this queue is a ScheduledFuture. For tasks submitted via one of the schedule methods, the element will be identical to the returned ScheduledFuture. For tasks submitted using execute, the element will be a zero-delay ScheduledFuture.

Iteration over this queue is not guaranteed to traverse tasks in the order in which they will execute.

Returns
`BlockingQueue<Runnable>`	the task queue

getRemoveOnCancelPolicy

Added in API level 21

public boolean getRemoveOnCancelPolicy ()

Gets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation. This value is by default false.

Returns
`boolean`	`true` if cancelled tasks are immediately removed from the queue

See also:

setRemoveOnCancelPolicy(boolean)

schedule

Added in API level 1

public ScheduledFuture<V> schedule (Callable<V> callable, 
                long delay, 
                TimeUnit unit)

Submits a value-returning one-shot task that becomes enabled after the given delay.

Parameters
`callable`	`Callable`: the function to execute
`delay`	`long`: the time from now to delay execution
`unit`	`TimeUnit`: the time unit of the delay parameter

Returns
`ScheduledFuture<V>`	a ScheduledFuture that can be used to extract result or cancel

Throws
`RejectedExecutionException`
`NullPointerException`

schedule

Added in API level 1

public ScheduledFuture<?> schedule (Runnable command, 
                long delay, 
                TimeUnit unit)

Submits a one-shot task that becomes enabled after the given delay.

Parameters
`command`	`Runnable`: the task to execute
`delay`	`long`: the time from now to delay execution
`unit`	`TimeUnit`: the time unit of the delay parameter

Returns
`ScheduledFuture<?>`	a ScheduledFuture representing pending completion of the task and whose `get()` method will return `null` upon completion

Throws
`RejectedExecutionException`
`NullPointerException`

scheduleAtFixedRate

Added in API level 1

public ScheduledFuture<?> scheduleAtFixedRate (Runnable command, 
                long initialDelay, 
                long period, 
                TimeUnit unit)

Submits 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.

The sequence of task executions continues indefinitely until one of the following exceptional completions occur:

The task is explicitly cancelled via the returned future.
Method shutdown() is called and the policy on whether to continue after shutdown is not set true, or method shutdownNow() is called; also resulting in task cancellation.
An execution of the task throws an exception. In this case calling get on the returned future will throw ExecutionException, holding the exception as its cause.

Subsequent executions are suppressed. Subsequent calls to isDone() on the returned future will return true.

Since API level 31: If the app is frozen by the Android cached apps freezer before the fixed rate task is done or canceled, the task may run many times immediately when the app unfreezes, just as if a single execution of the command had taken the duration of the frozen period to execute.

Since API level 36: If any execution of this task takes longer than its period, then the subsequent execution will be scheduled for the most recent missed period.

Parameters
`command`	`Runnable`: the task to execute
`initialDelay`	`long`: the time to delay first execution
`period`	`long`: the period between successive executions
`unit`	`TimeUnit`: the time unit of the initialDelay and period parameters

Returns
`ScheduledFuture<?>`	a ScheduledFuture representing pending completion of the series of repeated tasks. The future's `get()` method will never return normally, and will throw an exception upon task cancellation or abnormal termination of a task execution.

Throws
`RejectedExecutionException`
`NullPointerException`
`IllegalArgumentException`

scheduleWithFixedDelay

Added in API level 1

public ScheduledFuture<?> scheduleWithFixedDelay (Runnable command, 
                long initialDelay, 
                long delay, 
                TimeUnit unit)

Submits 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:

The task is explicitly cancelled via the returned future.
Method shutdown() is called and the policy on whether to continue after shutdown is not set true, or method shutdownNow() is called; also resulting in task cancellation.
An execution of the task throws an exception. In this case calling get on the returned future will throw ExecutionException, holding the exception as its cause.

Subsequent executions are suppressed. Subsequent calls to isDone() on the returned future will return true.

Parameters
`command`	`Runnable`: the task to execute
`initialDelay`	`long`: the time to delay first execution
`delay`	`long`: the delay between the termination of one execution and the commencement of the next
`unit`	`TimeUnit`: the time unit of the initialDelay and delay parameters

Returns
`ScheduledFuture<?>`	a ScheduledFuture representing pending completion of the series of repeated tasks. The future's `get()` method will never return normally, and will throw an exception upon task cancellation or abnormal termination of a task execution.

Throws
`RejectedExecutionException`
`NullPointerException`
`IllegalArgumentException`

setContinueExistingPeriodicTasksAfterShutdownPolicy

Added in API level 1

public void setContinueExistingPeriodicTasksAfterShutdownPolicy (boolean value)

Sets the policy on whether to continue executing existing periodic tasks even when this executor has been shutdown. In this case, executions will continue until shutdownNow or the policy is set to false when already shutdown. This value is by default false.

Parameters
`value`	`boolean`: if `true`, continue after shutdown, else don't

See also:

getContinueExistingPeriodicTasksAfterShutdownPolicy()

setExecuteExistingDelayedTasksAfterShutdownPolicy

Added in API level 1

public void setExecuteExistingDelayedTasksAfterShutdownPolicy (boolean value)

Sets the policy on whether to execute existing delayed tasks even when this executor has been shutdown. In this case, these tasks will only terminate upon shutdownNow, or after setting the policy to false when already shutdown. This value is by default true.

Parameters
`value`	`boolean`: if `true`, execute after shutdown, else don't

See also:

getExecuteExistingDelayedTasksAfterShutdownPolicy()

setRemoveOnCancelPolicy

Added in API level 21

public void setRemoveOnCancelPolicy (boolean value)

Sets the policy on whether cancelled tasks should be immediately removed from the work queue at time of cancellation. This value is by default false.

Parameters
`value`	`boolean`: if `true`, remove on cancellation, else don't

See also:

getRemoveOnCancelPolicy()

shutdown

Added in API level 1

public void shutdown ()

Initiates an orderly shutdown in which previously submitted tasks are executed, but no new tasks will be accepted. Invocation has no additional effect if already shut down.

This method does not wait for previously submitted tasks to complete execution. Use awaitTermination to do that.

If the ExecuteExistingDelayedTasksAfterShutdownPolicy has been set false, existing delayed tasks whose delays have not yet elapsed are cancelled. And unless the ContinueExistingPeriodicTasksAfterShutdownPolicy has been set true, future executions of existing periodic tasks will be cancelled.

shutdownNow

Added in API level 1

public List<Runnable> shutdownNow ()

Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution. These tasks are drained (removed) from the task queue upon return from this method.

This method does not wait for actively executing tasks to terminate. Use awaitTermination to do that.

There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. This implementation interrupts tasks via Thread.interrupt; any task that fails to respond to interrupts may never terminate.

Returns
`List<Runnable>`	list of tasks that never commenced execution. Each element of this list is a `ScheduledFuture`. For tasks submitted via one of the `schedule` methods, the element will be identical to the returned `ScheduledFuture`. For tasks submitted using `execute`, the element will be a zero-delay `ScheduledFuture`.

submit

Added in API level 1

public Future<?> submit (Runnable task)

Submits a Runnable task for execution and returns a Future representing that task. The Future's get method will return null upon successful completion.

Parameters
`task`	`Runnable`: the task to submit

Returns
`Future<?>`	a Future representing pending completion of the task

Throws
`RejectedExecutionException`
`NullPointerException`

submit

Added in API level 1

public Future<T> submit (Callable<T> task)

Submits a value-returning task for execution and returns a Future representing the pending results of the task. The Future's get method will return the task's result upon successful completion.

If you would like to immediately block waiting for a task, you can use constructions of the form result = exec.submit(aCallable).get();

Note: The Executors class includes a set of methods that can convert some other common closure-like objects, for example, PrivilegedAction to Callable form so they can be submitted.

Parameters
`task`	`Callable`: the task to submit

Returns
`Future<T>`	a Future representing pending completion of the task

Throws
`RejectedExecutionException`
`NullPointerException`

submit

Added in API level 1

public Future<T> submit (Runnable task, 
                T result)

Submits a Runnable task for execution and returns a Future representing that task. The Future's get method will return the given result upon successful completion.

Parameters
`task`	`Runnable`: the task to submit
`result`	`T`: the result to return

Returns
`Future<T>`	a Future representing pending completion of the task

Throws
`RejectedExecutionException`
`NullPointerException`

Protected methods

decorateTask

Added in API level 9

protected RunnableScheduledFuture<V> decorateTask (Runnable runnable, 
                RunnableScheduledFuture<V> task)

Modifies or replaces the task used to execute a runnable. This method can be used to override the concrete class used for managing internal tasks. The default implementation simply returns the given task.

Parameters
`runnable`	`Runnable`: the submitted Runnable
`task`	`RunnableScheduledFuture`: the task created to execute the runnable

Returns
`RunnableScheduledFuture<V>`	a task that can execute the runnable

decorateTask

Added in API level 9

protected RunnableScheduledFuture<V> decorateTask (Callable<V> callable, 
                RunnableScheduledFuture<V> task)

Modifies or replaces the task used to execute a callable. This method can be used to override the concrete class used for managing internal tasks. The default implementation simply returns the given task.

Parameters
`callable`	`Callable`: the submitted Callable
`task`	`RunnableScheduledFuture`: the task created to execute the callable

Returns
`RunnableScheduledFuture<V>`	a task that can execute the callable