Average of the Positive Numbers

/*
 * Problem : Average of positives.
 * Input   : n, then n integers.
 * Output  : The average or none.
 * Approach: Filter and reduce.
 * Time    : O(n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static String solve(int[] a) {
        // Step 1: Keep the positive numbers. The stream gives a summary with count and sum.
        java.util.LongSummaryStatistics stats = java.util.Arrays.stream(a).filter(v -> v > 0).asLongStream().summaryStatistics();
        // Step 2: With no positive number there is no answer. Optional models "no value" without a special number.
        java.util.Optional<Long> average = stats.getCount() == 0 ? java.util.Optional.<Long>empty() : java.util.Optional.of(stats.getSum() / stats.getCount());
        return average.map(String::valueOf).orElse("none");
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        int[] a = new int[size];
        for (int i = 0; i < size; i++) {
            a[i] = scanner.nextInt();
        }
        System.out.println(solve(a));
    }
}