线程池

       // 最上级 Executor
        // 第二级 ExecutorService
        // 第三级 AbstractExecutorService
        // 再来就是ThreadPoolExecutor
        ThreadPoolExecutor executor = new ThreadPoolExecutor(
                10, 20,
                10L, TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(10));

        /*
        new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
         */
        ExecutorService fixedThreadPool = Executors.newFixedThreadPool(10);

        /*
        new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>()));
         */
        ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();

        /*
        new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
         */
        ExecutorService cachedThreadPool = Executors.newCachedThreadPool();