例子：

ExecutorService es = Executors.newCachedThreadPool();
        try {
            for (int i = 0; i < 20; i++) {
                Runnable syncRunnable = new Runnable() {
                    @Override
                    public void run() {
                        log.info(Thread.currentThread().getName());
                        
 
try {
                            Thread.sleep(2000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                };
                es.execute(syncRunnable);
            }
        } finally {
            es.shutdown();
        }
 

運行結果：

            10:21:04.610 pool-1-thread-13
            10:21:04.612 pool-1-thread-3
            10:21:04.612 pool-1-thread-7
            10:21:04.612 pool-1-thread-2
            10:21:04.610 pool-1-thread-14
            10:21:04.612 pool-1-thread-6
            10:21:04.611 pool-1-thread-8
            10:21:04.611 pool-1-thread-11
            10:21:04.611 pool-1-thread-4
            10:21:04.610 pool-1-thread-1
            10:21:04.611 pool-1-thread-20
            10:21:04.611 pool-1-thread-12
            10:21:04.610 pool-1-thread-16
            10:21:04.611 pool-1-thread-5
            10:21:04.611 pool-1-thread-9
            10:21:04.610 pool-1-thread-17
            10:21:04.610 pool-1-thread-18
            10:21:04.610 pool-1-thread-10
            10:21:04.611 pool-1-thread-15
            10:21:04.611 pool-1-thread-19

調用的調用的ThreadPoolExecutor：

public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }

corePoolSize=0，maximumPoolSize=Integer.MAX_VALUE

keepAliveTime=60秒

allowCoreThreadTimeout=false（默認）

因此，

• 核心線程數為0
• 每來一個任務，先查看緩沖池中是否有可用線程（沒超過60秒的），如果有，則用；沒有，則就創建一個新線程
• 因為核心線程數為0，池中的線程當達到60秒時，會超時關閉，直到核心線程數=0

線程池（3）Executors.newCachedThreadPool