public static void main(String[] args) {
    System.out.println("Enter a number of elements in the array:");
    Scanner scanner = new Scanner(System.in);
    int n = scanner.nextInt();
    ArrayList<Integer> array = new ArrayList<>();
    for (int i = 0; i < n; i++) {
        array.add((int)(Math.random() * 10));
    }
    Stream<Integer> stream = array.stream();
    double average = array.stream().average();
    System.out.print(average);
}

OptionalDouble average = array.stream().mapToInt(e -> e).average();
if (average.isPresent())
{
    System.out.print(average.getAsDouble());
}