Parallel foreach in Java

List<Integer> listOfNumbers = Arrays.asList(1, 2, 3, 4);
listOfNumbers.parallelStream().forEach(number ->
    System.out.println(number + " " + Thread.currentThread().getName())
);

Custom Thread Pool

List<Integer> listOfNumbers = Arrays.asList(1, 2, 3, 4);
ForkJoinPool customThreadPool = new ForkJoinPool(4);
int sum = customThreadPool.submit(
    () -> listOfNumbers.parallelStream().reduce(0, Integer::sum)).get();
customThreadPool.shutdown();
assertThat(sum).isEqualTo(10);

References
https://www.baeldung.com/java-when-to-use-parallel-stream