ExecutorService executorService = Executors.newFixedThreadPool(10); for (int i = 0; i < 100; i++) { Runnable task = new MyTask(); executorService.submit(task); } executorService.shutdown(); ConcurrentMap<String, Integer> concurrentMap = new ConcurrentHashMap<>(); concurrentMap.put("key1", 1); concurrentMap.put("key2", 2); Integer value = concurrentMap.get("key1"); System.out.println(value); AtomicInteger atomicInteger = new AtomicInteger(0); atomicInteger.incrementAndGet(); System.out.println(atomicInteger.get());