Four ways to create thread pools

newCachedThreadPool
Create a cacheable thread pool , Create... As needed , There used to be reusing them

newFixedThreadPool
Create a fixed thread pool , reusable

newScheduledThredPool
Create a thread pool , Arrange plan execution （ regular ）

 public static void main(String[] args) {
        ScheduledExecutorService scheduledThreadPool =  Executors.newScheduledThreadPool(3);
        scheduledThreadPool.schedule(new Runnable() {
            @Override
            public void run() {
                System.out.println(" etc. 3 second ");
            }
        }, 3, TimeUnit.SECONDS);

        scheduledThreadPool.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                System.out.println(" Execute every three seconds after a delay of one second ");
            }
        }, 1, 3, TimeUnit.SECONDS);

        scheduledThreadPool.scheduleAtFixedRate(() -> {
            System.out.println("===============");
        }, 1, 3, TimeUnit.SECONDS);
    }

result

 Execute every three seconds after a delay of one second 
===============
 etc. 3 second 
 Execute every three seconds after a delay of one second 
===============
 Execute every three seconds after a delay of one second 
===============
 Execute every three seconds after a delay of one second 
===============
 Execute every three seconds after a delay of one second 
===============

newSingleThreadExecutor
Single instance execution , This thread pool has only one thread , This thread can restart a thread after the thread exception to continue to execute instead of the original thread