CompletableFuture<?>[] completableFutures = runnables.stream()

    .map(CompletableFuture::runAsync)

    .toArray(CompletableFuture<?>[]::new);

boolean isEveryRunnableDone = CompletableFuture.allOf(completableFutures)

    .isDone();

ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors.newFixedThreadPool(5);

runnables.forEach(executor::execute);