public static void main(String[] args) {
    ExecutorService executorService = Executors.newFixedThreadPool(10);

    for (int i = 0; i < 10; i++) {
        CompletableFuture<String> stringCf = CompletableFuture.supplyAsync(() -> {
            try {
                System.out.println(Thread.currentThread().getName());
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName());
            return "done";

        }, executorService);
     //  System.out.println(stringCf.get().toString()); if you add this it works

    }