# Class AbstractExecutorService

java.lang.Object
java.util.concurrent.AbstractExecutorService

All Implemented Interfaces:
  `AutoCloseable, Executor, ExecutorService`

Direct Known Subclasses:
  `ForkJoinPool, ThreadPoolExecutor`

public abstract class AbstractExecutorService extends Object implements ExecutorService
Provides default implementations of `ExecutorService` execution methods. This class implements the `submit`, `invokeAny` and `invokeAll` methods using a `RunnableFuture` returned by `newTaskFor`, which defaults to the `FutureTask` class provided in this package. For example, the implementation of `submit(Runnable)` creates an associated `RunnableFuture` that is executed and returned. Subclasses may override the `newTaskFor` methods to return `RunnableFuture` implementations other than `FutureTask`.

Extension example. Here is a sketch of a class that customizes `ThreadPoolExecutor` to use a `CustomTask` class instead of the default `FutureTask`:

    public class CustomThreadPoolExecutor extends ThreadPoolExecutor {

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

      protected <V> RunnableFuture<V> newTaskFor(Callable<V> c) {
          return new CustomTask<V>(c);
      }
      protected <V> RunnableFuture<V> newTaskFor(Runnable r, V v) {
          return new CustomTask<V>(r, v);
      }
      // ... add constructors, etc.
    }

Since:
  1.5

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `AbstractExecutorService()`
  Constructor for subclasses to call.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `<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.
  `protected <T> RunnableFuture<T>`
  `newTaskFor(Runnable runnable, T value)`
  Returns a `RunnableFuture` for the given runnable and default value.
  `protected <T> RunnableFuture<T>`
  `newTaskFor(Callable<T> callable)`
  Returns a `RunnableFuture` for the given callable task.
  `Future<?>`
  `submit(Runnable task)`
  Submits a Runnable task for execution and returns a Future representing that task.
  `<T> Future<T>`
  `submit(Runnable task, T result)`
  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.

  ### Methods declared in class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

  ### Methods declared in interface Executor

  `execute`

  ### Methods declared in interface ExecutorService

  `awaitTermination, close, isShutdown, isTerminated, shutdown, shutdownNow`

- ## Constructor Details

  - ### AbstractExecutorService

    public AbstractExecutorService()
    Constructor for subclasses to call.

- ## Method Details

  - ### newTaskFor

    protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value)
    Returns a `RunnableFuture` for the given runnable and default value.
    Type Parameters:
      `T` - the type of the given value
    Parameters:
      `runnable` - the runnable task being wrapped
      `value` - the default value for the returned future
    Returns:
      a `RunnableFuture` which, when run, will run the underlying runnable and which, as a `Future`, will yield the given value as its result and provide for cancellation of the underlying task
    Since:
      1.6

  - ### newTaskFor

    protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable)
    Returns a `RunnableFuture` for the given callable task.
    Type Parameters:
      `T` - the type of the callable's result
    Parameters:
      `callable` - the callable task being wrapped
    Returns:
      a `RunnableFuture` which, when run, will call the underlying callable and which, as a `Future`, will yield the callable's result as its result and provide for cancellation of the underlying task
    Since:
      1.6

  - ### submit

    public Future<?> submit(Runnable task)
    Description copied from interface: `ExecutorService`
    Submits a Runnable task for execution and returns a Future representing that task. The Future's `get` method will return `null` upon successful completion.
    Specified by:
      `submit` in interface `ExecutorService`
    Parameters:
      `task` - the task to submit
    Returns:
      a Future representing pending completion of the task
    Throws:
      `RejectedExecutionException` - if the task cannot be scheduled for execution
      `NullPointerException` - if the task is null

  - ### submit

    public <T> Future<T> submit(Runnable task, T result)
    Description copied from interface: `ExecutorService`
    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.
    Specified by:
      `submit` in interface `ExecutorService`
    Type Parameters:
      `T` - the type of the result
    Parameters:
      `task` - the task to submit
      `result` - the result to return
    Returns:
      a Future representing pending completion of the task
    Throws:
      `RejectedExecutionException` - if the task cannot be scheduled for execution
      `NullPointerException` - if the task is null

  - ### submit

    public <T> Future<T> submit(Callable<T> task)
    Description copied from interface: `ExecutorService`
    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.

    Specified by:
      `submit` in interface `ExecutorService`
    Type Parameters:
      `T` - the type of the task's result
    Parameters:
      `task` - the task to submit
    Returns:
      a Future representing pending completion of the task
    Throws:
      `RejectedExecutionException` - if the task cannot be scheduled for execution
      `NullPointerException` - if the task is null

  - ### invokeAny

    public <T> T invokeAny(Collection<? extends Callable<T>> tasks) throws InterruptedException, ExecutionException
    Description copied from interface: `ExecutorService`
    Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress.
    Specified by:
      `invokeAny` in interface `ExecutorService`
    Type Parameters:
      `T` - the type of the values returned from the tasks
    Parameters:
      `tasks` - the collection of tasks
    Returns:
      the result returned by one of the tasks
    Throws:
      `InterruptedException` - if interrupted while waiting
      `NullPointerException` - if tasks or any element task subject to execution is `null`
      `IllegalArgumentException` - if tasks is empty
      `ExecutionException` - if no task successfully completes
      `RejectedExecutionException` - if tasks cannot be scheduled for execution

  - ### invokeAny

    public <T> T invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
    Description copied from interface: `ExecutorService`
    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. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress.
    Specified by:
      `invokeAny` in interface `ExecutorService`
    Type Parameters:
      `T` - the type of the values returned from the tasks
    Parameters:
      `tasks` - the collection of tasks
      `timeout` - the maximum time to wait
      `unit` - the time unit of the timeout argument
    Returns:
      the result returned by one of the tasks
    Throws:
      `InterruptedException` - if interrupted while waiting
      `NullPointerException` - if tasks, or unit, or any element task subject to execution is `null`
      `TimeoutException` - if the given timeout elapses before any task successfully completes
      `ExecutionException` - if no task successfully completes
      `RejectedExecutionException` - if tasks cannot be scheduled for execution

  - ### invokeAll

    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) throws InterruptedException
    Description copied from interface: `ExecutorService`
    Executes the given tasks, returning a list of Futures holding their status and results when all complete. `Future.isDone()` is `true` for each element of the returned list. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress.
    Specified by:
      `invokeAll` in interface `ExecutorService`
    Type Parameters:
      `T` - the type of the values returned from the tasks
    Parameters:
      `tasks` - the collection of tasks
    Returns:
      a list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list, each of which has completed
    Throws:
      `InterruptedException` - if interrupted while waiting, in which case unfinished tasks are cancelled
      `NullPointerException` - if tasks or any of its elements are `null`
      `RejectedExecutionException` - if any task cannot be scheduled for execution

  - ### invokeAll

    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit) throws InterruptedException
    Description copied from interface: `ExecutorService`
    Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first. `Future.isDone()` is `true` for each element of the returned list. Upon return, tasks that have not completed are cancelled. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress.
    Specified by:
      `invokeAll` in interface `ExecutorService`
    Type Parameters:
      `T` - the type of the values returned from the tasks
    Parameters:
      `tasks` - the collection of tasks
      `timeout` - the maximum time to wait
      `unit` - the time unit of the timeout argument
    Returns:
      a list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list. If the operation did not time out, each task will have completed. If it did time out, some of these tasks will not have completed.
    Throws:
      `InterruptedException` - if interrupted while waiting, in which case unfinished tasks are cancelled
      `NullPointerException` - if tasks, any of its elements, or unit are `null`
      `RejectedExecutionException` - if any task cannot be scheduled for execution