Java中线程池的实现原理是什么

    @Test  public void threadPool(){        CountDownLatch count = new CountDownLatch(50000);    long start = System.currentTimeMillis();    Executor pool = Executors.newFixedThreadPool(10);//开启线程池最多会创建10个线程    for(int i=0;i<50000;i++){      pool.execute(new Runnable() {        @Override        public void run() {          System.out.println("hello");          count.countDown();        }      });    }    while(count.getCount()!=0){//堵塞等待5w个线程运行完毕    }    long end = System.currentTimeMillis();    System.out.println("50个线程都执行完了,共用时:"+(end-start)+"ms");  }    @Test  public void thread(){    CountDownLatch count = new CountDownLatch(50000);    long start = System.currentTimeMillis();    for(int i=0;i<50000;i++){      Thread thread = new Thread(new Runnable() {        @Override        public void run() {          System.out.println("hello");          count.countDown();        }      });      thread.start();    }    while(count.getCount()!=0){//堵塞等待5w个线程运行完毕    }    long end = System.currentTimeMillis();    System.out.println("50000个线程都执行完了,共用时:"+(end-start)+"ms");  }