Concatenar Listas de numeros - Java

Implementar metodo que concatena todos los numeros positivos de dos listas.

class ConcatPositiveNumbersProblem {

    public static ArrayList<Integer> concatPositiveNumbers(ArrayList<Integer> l1, ArrayList<Integer> l2) {
        ArrayList<Integer> numbers = new ArrayList<>();
        for (int num : l1) {
            if (num >= 0) {
                numbers.add(num);
            }
        }
        for (int num : l2) {
            if (num >= 0) {
                numbers.add(num);
            }
        }
        return numbers;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        ArrayList<Integer> list1 = readArrayList(scanner);
        ArrayList<Integer> list2 = readArrayList(scanner);

        ArrayList<Integer> result = concatPositiveNumbers(list1, list2);

        result.forEach(n -> System.out.print(n + " "));
    }

    private static ArrayList<Integer> readArrayList(Scanner scanner) {
        return Arrays
                .stream(scanner.nextLine().split("\\s+"))
                .map(Integer::parseInt)
                .collect(Collectors.toCollection(ArrayList::new));
    }
}