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## java.util.concurrent
Interface Executor

All Known Subinterfaces:
  ExecutorService, ScheduledExecutorService

All Known Implementing Classes:
  AbstractExecutorService, ScheduledThreadPoolExecutor, ThreadPoolExecutor

    public interface Executor

An object that executes submitted `Runnable` tasks. This interface provides a way of decoupling task submission from the mechanics of how each task will be run, including details of thread use, scheduling, etc. An `Executor` is normally used instead of explicitly creating threads. For example, rather than invoking `new Thread(new(RunnableTask())).start()` for each of a set of tasks, you might use:

     Executor executor = anExecutor;
     executor.execute(new RunnableTask1());
     executor.execute(new RunnableTask2());
     ...

However, the `Executor` interface does not strictly require that execution be asynchronous. In the simplest case, an executor can run the submitted task immediately in the caller's thread:

     class DirectExecutor implements Executor {
         public void execute(Runnable r) {
             r.run();
         }
     }

More typically, tasks are executed in some thread other than the caller's thread. The executor below spawns a new thread for each task.

     class ThreadPerTaskExecutor implements Executor {
         public void execute(Runnable r) {
             new Thread(r).start();
         }
     }

Many `Executor` implementations impose some sort of limitation on how and when tasks are scheduled. The executor below serializes the submission of tasks to a second executor, illustrating a composite executor.

     class SerialExecutor implements Executor {
         final Queue<Runnable> tasks = new ArrayDeque<Runnable>();
         final Executor executor;
         Runnable active;

         SerialExecutor(Executor executor) {
             this.executor = executor;
         }

         public synchronized void execute(final Runnable r) {
             tasks.offer(new Runnable() {
                 public void run() {
                     try {
                         r.run();
                     } finally {
                         scheduleNext();
                     }
                 }
             });
             if (active == null) {
                 scheduleNext();
             }
         }

         protected synchronized void scheduleNext() {
             if ((active = tasks.poll()) != null) {
                 executor.execute(active);
             }
         }
     }

The `Executor` implementations provided in this package implement `ExecutorService`, which is a more extensive interface. The `ThreadPoolExecutor` class provides an extensible thread pool implementation. The `Executors` class provides convenient factory methods for these Executors.

Memory consistency effects: Actions in a thread prior to submitting a `Runnable` object to an `Executor` happen-before its execution begins, perhaps in another thread.

Since:
  1.5

Method Summary
`void` | `execute(Runnable command)` Executes the given command at some time in the future.

Method Detail

### execute

    void execute(Runnable command)

  Executes the given command at some time in the future. The command may execute in a new thread, in a pooled thread, or in the calling thread, at the discretion of the `Executor` implementation.

  Parameters:
    `command` - the runnable task
  Throws:
    `RejectedExecutionException` - if this task cannot be accepted for execution.
    `NullPointerException` - if command is null

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For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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