Executor

public interface Executor {    /**     * 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 {@code Executor} implementation.     *     * @param command the runnable task     * @throws RejectedExecutionException if this task cannot be     * accepted for execution     * @throws NullPointerException if command is null     */    void execute(Runnable command);}

command的执行可能在一个新线程，也可能在一个线程池中，或者在调用线程，具体由Executor到实现者决定。

可以自自定义实现Executor，官方实现有ExecutorService，ThreadPoolExecutor，Executors。

Executors是个工具类，能返回ExecutorService，ScheduledExecutorService，a "wrapped" ExecutorService，ThreadFactory，Callable。

public interface ThreadFactory {    /**     * Constructs a new {@code Thread}.  Implementations may also initialize     * priority, name, daemon status, {@code ThreadGroup}, etc.     *     * @param r a runnable to be executed by new thread instance     * @return constructed thread, or {@code null} if the request to     *         create a thread is rejected     */    Thread newThread(Runnable r);}

Executors中创建DefaultThreadFactory

    /**     * The default thread factory     */    static class DefaultThreadFactory implements ThreadFactory {        private static final AtomicInteger poolNumber = new AtomicInteger(1);        private final ThreadGroup group;        private final AtomicInteger threadNumber = new AtomicInteger(1);        private final String namePrefix;        DefaultThreadFactory() {            SecurityManager s = System.getSecurityManager();            group = (s != null) ? s.getThreadGroup() :                                  Thread.currentThread().getThreadGroup();            namePrefix = "pool-" +                          poolNumber.getAndIncrement() +                         "-thread-";        }        public Thread newThread(Runnable r) {            Thread t = new Thread(group, r,                                  namePrefix + threadNumber.getAndIncrement(),                                  0);            if (t.isDaemon())                t.setDaemon(false);            if (t.getPriority() != Thread.NORM_PRIORITY)                t.setPriority(Thread.NORM_PRIORITY);            return t;        }    }