public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue());
}
該線程池在極端情況下,每次提交新的任務都會創建新的線程執行. 適合用來執行大量耗時短并且提交頻繁的任務

    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue());
    }

    public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue()));
    }

ThreadPoolExecutor的構造方法:
    public ThreadPoolExecutor(int corePoolSize,
                                   int maximumPoolSize,
                                   long keepAliveTime,
                                   TimeUnit unit,
                                   BlockingQueue workQueue,
                                   ThreadFactory threadFactory,
                                   RejectedExecutionHandler handler)