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Summary: Methods | Inherited Methods

# Executors

`public class Executors`
`extends Object` ``

java.lang.Object
↳ | java.util.concurrent.Executors

Factory and utility methods for `Executor`, `ExecutorService`, `ScheduledExecutorService`, `ThreadFactory`, and `Callable` classes defined in this package. This class supports the following kinds of methods:

- Methods that create and return an `ExecutorService` set up with commonly useful configuration settings.
- Methods that create and return a `ScheduledExecutorService` set up with commonly useful configuration settings.
- Methods that create and return a "wrapped" ExecutorService, that disables reconfiguration by making implementation-specific methods inaccessible.
- Methods that create and return a `ThreadFactory` that sets newly created threads to a known state.
- Methods that create and return a `Callable` out of other closure-like forms, so they can be used in execution methods requiring `Callable`.

## Summary

### Public methods
`static Callable<Object>` | `callable(Runnable task)` Returns a `Callable` object that, when called, runs the given task and returns `null`.
`static Callable<Object>` | `callable(PrivilegedAction<?> action)` Returns a `Callable` object that, when called, runs the given privileged action and returns its result.
`static Callable<Object>` | `callable(PrivilegedExceptionAction<?> action)` Returns a `Callable` object that, when called, runs the given privileged exception action and returns its result.
`static <T> Callable<T>` | `callable(Runnable task, T result)` Returns a `Callable` object that, when called, runs the given task and returns the given result.
`static ThreadFactory` | `defaultThreadFactory()` Returns a default thread factory used to create new threads.
`static ExecutorService` | `newCachedThreadPool()` Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available.
`static ExecutorService` | `newCachedThreadPool(ThreadFactory threadFactory)` Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available, and uses the provided ThreadFactory to create new threads when needed.
`static ExecutorService` | `newFixedThreadPool(int nThreads, ThreadFactory threadFactory)` Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue, using the provided ThreadFactory to create new threads when needed.
`static ExecutorService` | `newFixedThreadPool(int nThreads)` Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue.
`static ScheduledExecutorService` | `newScheduledThreadPool(int corePoolSize)` Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.
`static ScheduledExecutorService` | `newScheduledThreadPool(int corePoolSize, ThreadFactory threadFactory)` Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.
`static ExecutorService` | `newSingleThreadExecutor(ThreadFactory threadFactory)` Creates an Executor that uses a single worker thread operating off an unbounded queue, and uses the provided ThreadFactory to create a new thread when needed.
`static ExecutorService` | `newSingleThreadExecutor()` Creates an Executor that uses a single worker thread operating off an unbounded queue.
`static ScheduledExecutorService` | `newSingleThreadScheduledExecutor()` Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically.
`static ScheduledExecutorService` | `newSingleThreadScheduledExecutor(ThreadFactory threadFactory)` Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically.
`static ExecutorService` | `newWorkStealingPool(int parallelism)` Creates a thread pool that maintains enough threads to support the given parallelism level, and may use multiple queues to reduce contention.
`static ExecutorService` | `newWorkStealingPool()` Creates a work-stealing thread pool using the number of Runtime#availableProcessors as its target parallelism level.
`static <T> Callable<T>` | `privilegedCallable(Callable<T> callable)` Legacy security code; do not use.
`static <T> Callable<T>` | `privilegedCallableUsingCurrentClassLoader(Callable<T> callable)` Legacy security code; do not use.
`static ThreadFactory` | `privilegedThreadFactory()` Legacy security code; do not use.
`static ExecutorService` | `unconfigurableExecutorService(ExecutorService executor)` Returns an object that delegates all defined `ExecutorService` methods to the given executor, but not any other methods that might otherwise be accessible using casts.
`static ScheduledExecutorService` | `unconfigurableScheduledExecutorService(ScheduledExecutorService executor)` Returns an object that delegates all defined `ScheduledExecutorService` methods to the given executor, but not any other methods that might otherwise be accessible using casts.

### Inherited methods
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 timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

## Public methods

### callable

    public static Callable<Object> callable (Runnable task)

Returns a `Callable` object that, when called, runs the given task and returns `null`.

Parameters
`task` | `Runnable`: the task to run

Returns
`Callable<Object>` | a callable object

Throws
`NullPointerException` | if task null

### callable

    public static Callable<Object> callable (PrivilegedAction<?> action)

Returns a `Callable` object that, when called, runs the given privileged action and returns its result.

Parameters
`action` | `PrivilegedAction`: the privileged action to run

Returns
`Callable<Object>` | a callable object

Throws
`NullPointerException` | if action null

### callable

    public static Callable<Object> callable (PrivilegedExceptionAction<?> action)

Returns a `Callable` object that, when called, runs the given privileged exception action and returns its result.

Parameters
`action` | `PrivilegedExceptionAction`: the privileged exception action to run

Returns
`Callable<Object>` | a callable object

Throws
`NullPointerException` | if action null

### callable

    public static Callable<T> callable (Runnable task,
                    T result)

Returns a `Callable` object that, when called, runs the given task and returns the given result. This can be useful when applying methods requiring a `Callable` to an otherwise resultless action.

Parameters
`task` | `Runnable`: the task to run
`result` | `T`: the result to return

Returns
`Callable<T>` | a callable object

Throws
`NullPointerException` | if task null

### defaultThreadFactory

    public static ThreadFactory defaultThreadFactory ()

Returns a default thread factory used to create new threads. This factory creates all new threads used by an Executor in the same `ThreadGroup`. Each new thread is created as a non-daemon thread with priority set to the smaller of `Thread.NORM_PRIORITY` and the maximum priority permitted in the thread group. New threads have names accessible via `Thread#getName` of pool-N-thread-M, where N is the sequence number of this factory, and M is the sequence number of the thread created by this factory.

Returns
`ThreadFactory` | a thread factory

### newCachedThreadPool

    public static ExecutorService newCachedThreadPool ()

Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available. These pools will typically improve the performance of programs that execute many short-lived asynchronous tasks. Calls to `execute` will reuse previously constructed threads if available. If no existing thread is available, a new thread will be created and added to the pool. Threads that have not been used for sixty seconds are terminated and removed from the cache. Thus, a pool that remains idle for long enough will not consume any resources. Note that pools with similar properties but different details (for example, timeout parameters) may be created using `ThreadPoolExecutor` constructors.

Returns
`ExecutorService` | the newly created thread pool

### newCachedThreadPool

    public static ExecutorService newCachedThreadPool (ThreadFactory threadFactory)

Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available, and uses the provided ThreadFactory to create new threads when needed.

Parameters
`threadFactory` | `ThreadFactory`: the factory to use when creating new threads

Returns
`ExecutorService` | the newly created thread pool

Throws
`NullPointerException` | if threadFactory is null

### newFixedThreadPool

    public static ExecutorService newFixedThreadPool (int nThreads,
                    ThreadFactory threadFactory)

Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue, using the provided ThreadFactory to create new threads when needed. At any point, at most `nThreads` threads will be active processing tasks. If additional tasks are submitted when all threads are active, they will wait in the queue until a thread is available. If any thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks. The threads in the pool will exist until it is explicitly `ExecutorService#shutdown`.

Parameters
`nThreads` | `int`: the number of threads in the pool
`threadFactory` | `ThreadFactory`: the factory to use when creating new threads

Returns
`ExecutorService` | the newly created thread pool

Throws
`NullPointerException` | if threadFactory is null
`IllegalArgumentException` | if `nThreads <= 0`

### newFixedThreadPool

    public static ExecutorService newFixedThreadPool (int nThreads)

Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue. At any point, at most `nThreads` threads will be active processing tasks. If additional tasks are submitted when all threads are active, they will wait in the queue until a thread is available. If any thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks. The threads in the pool will exist until it is explicitly `ExecutorService#shutdown`.

Parameters
`nThreads` | `int`: the number of threads in the pool

Returns
`ExecutorService` | the newly created thread pool

Throws
`IllegalArgumentException` | if `nThreads <= 0`

### newScheduledThreadPool

    public static ScheduledExecutorService newScheduledThreadPool (int corePoolSize)

Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.

Parameters
`corePoolSize` | `int`: the number of threads to keep in the pool, even if they are idle

Returns
`ScheduledExecutorService` | a newly created scheduled thread pool

Throws
`IllegalArgumentException` | if `corePoolSize < 0`

### newScheduledThreadPool

    public static ScheduledExecutorService newScheduledThreadPool (int corePoolSize,
                    ThreadFactory threadFactory)

Creates a thread pool that can schedule commands to run after a given delay, or to execute periodically.

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

Returns
`ScheduledExecutorService` | a newly created scheduled thread pool

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

### newSingleThreadExecutor

    public static ExecutorService newSingleThreadExecutor (ThreadFactory threadFactory)

Creates an Executor that uses a single worker thread operating off an unbounded queue, and uses the provided ThreadFactory to create a new thread when needed. Unlike the otherwise equivalent `newFixedThreadPool(1, threadFactory)` the returned executor is guaranteed not to be reconfigurable to use additional threads.

Parameters
`threadFactory` | `ThreadFactory`: the factory to use when creating new threads

Returns
`ExecutorService` | the newly created single-threaded Executor

Throws
`NullPointerException` | if threadFactory is null

### newSingleThreadExecutor

    public static ExecutorService newSingleThreadExecutor ()

Creates an Executor that uses a single worker thread operating off an unbounded queue. (Note however that if this single thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks.) Tasks are guaranteed to execute sequentially, and no more than one task will be active at any given time. Unlike the otherwise equivalent `newFixedThreadPool(1)` the returned executor is guaranteed not to be reconfigurable to use additional threads.

Returns
`ExecutorService` | the newly created single-threaded Executor

### newSingleThreadScheduledExecutor

    public static ScheduledExecutorService newSingleThreadScheduledExecutor ()

Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically. (Note however that if this single thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks.) Tasks are guaranteed to execute sequentially, and no more than one task will be active at any given time. Unlike the otherwise equivalent `newScheduledThreadPool(1)` the returned executor is guaranteed not to be reconfigurable to use additional threads.

Returns
`ScheduledExecutorService` | the newly created scheduled executor

### newSingleThreadScheduledExecutor

    public static ScheduledExecutorService newSingleThreadScheduledExecutor (ThreadFactory threadFactory)

Creates a single-threaded executor that can schedule commands to run after a given delay, or to execute periodically. (Note however that if this single thread terminates due to a failure during execution prior to shutdown, a new one will take its place if needed to execute subsequent tasks.) Tasks are guaranteed to execute sequentially, and no more than one task will be active at any given time. Unlike the otherwise equivalent `newScheduledThreadPool(1, threadFactory)` the returned executor is guaranteed not to be reconfigurable to use additional threads.

Parameters
`threadFactory` | `ThreadFactory`: the factory to use when creating new threads

Returns
`ScheduledExecutorService` | a newly created scheduled executor

Throws
`NullPointerException` | if threadFactory is null

### newWorkStealingPool

    public static ExecutorService newWorkStealingPool (int parallelism)

Creates a thread pool that maintains enough threads to support the given parallelism level, and may use multiple queues to reduce contention. The parallelism level corresponds to the maximum number of threads actively engaged in, or available to engage in, task processing. The actual number of threads may grow and shrink dynamically. A work-stealing pool makes no guarantees about the order in which submitted tasks are executed.

Parameters
`parallelism` | `int`: the targeted parallelism level

Returns
`ExecutorService` | the newly created thread pool

Throws
`IllegalArgumentException` | if `parallelism <= 0`

### newWorkStealingPool

    public static ExecutorService newWorkStealingPool ()

Creates a work-stealing thread pool using the number of Runtime#availableProcessors as its target parallelism level.

Returns
`ExecutorService` | the newly created thread pool

See also:

- `newWorkStealingPool(int)`

### privilegedCallable

    public static Callable<T> privilegedCallable (Callable<T> callable)

Legacy security code; do not use.

Parameters
`callable` | `Callable`

Returns
`Callable<T>` |

### privilegedCallableUsingCurrentClassLoader

    public static Callable<T> privilegedCallableUsingCurrentClassLoader (Callable<T> callable)

Legacy security code; do not use.

Parameters
`callable` | `Callable`

Returns
`Callable<T>` |

### privilegedThreadFactory

    public static ThreadFactory privilegedThreadFactory ()

Legacy security code; do not use.

Returns
`ThreadFactory` |

### unconfigurableExecutorService

    public static ExecutorService unconfigurableExecutorService (ExecutorService executor)

Returns an object that delegates all defined `ExecutorService` methods to the given executor, but not any other methods that might otherwise be accessible using casts. This provides a way to safely "freeze" configuration and disallow tuning of a given concrete implementation.

Parameters
`executor` | `ExecutorService`: the underlying implementation

Returns
`ExecutorService` | an `ExecutorService` instance

Throws
`NullPointerException` | if executor null

### unconfigurableScheduledExecutorService

    public static ScheduledExecutorService unconfigurableScheduledExecutorService (ScheduledExecutorService executor)

Returns an object that delegates all defined `ScheduledExecutorService` methods to the given executor, but not any other methods that might otherwise be accessible using casts. This provides a way to safely "freeze" configuration and disallow tuning of a given concrete implementation.

Parameters
`executor` | `ScheduledExecutorService`: the underlying implementation

Returns
`ScheduledExecutorService` | a `ScheduledExecutorService` instance

Throws
`NullPointerException` | if executor null

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