ExecutorService executor = Executors.newFixedThreadPool(5); executor.execute(new RunnableTask()); ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>(); map.put("key1", 1); map.put("key2", 2); System.out.println(map.get("key1")); AtomicInteger counter = new AtomicInteger(); counter.incrementAndGet(); System.out.println(counter.get());