Comparaison of Java 7 and Java 8 style

Exercice6.java

import java.util.concurrent.TimeUnit;
import java.util.function.Supplier;
import java.util.stream.IntStream;

/**
 * I tried to compare Java 7 and Java 8 (functional way) syntax on a small problem.
 * I Also compare performances just for fun.
 */
public class Exercice6 {


    private static final int MAX_MINUTES = 60;
    private static final int MAX_HOURS = 24;

    /**
     * Consider an alarm leds displaying the hours and minutes in 24-hour format.
     * Question: What is the maximum value reached by the sum of 4 digits?
     */

    private static int java7() {
        // Old style
        int maxSum = 0;
        for (int hour = 0; hour < MAX_HOURS; hour++) { // possible hours
            for (int minute = 0; minute < MAX_MINUTES; minute++) { // possible minutes
                String display = Integer.toString(hour) + Integer.toString(minute); // generate display
                // Calculate sum of digits
                int sum = 0;
                for (char digit : display.toCharArray()) {
                    sum += Character.getNumericValue(digit);
                }
                // Memorize max
                if (sum > maxSum) {
                    maxSum = sum;
                }
            }
        }
        return maxSum;
    }

    private static int java8() {
        // New Java8 style
        return IntStream.range(0, MAX_HOURS).boxed() // possible hours
                .flatMap(hour -> IntStream.range(0, MAX_MINUTES).boxed() // possible minutes
                        .map(minute -> hour.toString() + minute.toString())) // generate dislays
                        // Get sum of digits
                .map(diplay -> diplay.chars().map(Character::getNumericValue).reduce(0, (n1, n2) -> n1 + n2))
                        // Find max
                .max(Integer::compare)
                        // Display the result if present.
                .get();
    }


    private static long chrono(Supplier<Integer> algo) {
        long startTime = System.nanoTime();
        int result = algo.get();
        long elapsedTime = System.nanoTime() - startTime;
        if (result != 24) {
            throw new AssertionError();
        }
        return elapsedTime;
    }

    public static void main(String[] args) {


        // Warm up
        for (int i = 0; i < 10000; i++) {
            java7();
            java8();
        }

        long java7Time = 0;
        long java8Time = 0;

        for (int i = 0; i < 10000; i++) {
            java8Time += chrono(Exercice6::java8);
            java7Time += chrono(Exercice6::java7);
        }

        System.out.println("Total time for Java 7 : " + TimeUnit.NANOSECONDS.toMillis(java7Time) + "ms");
        System.out.println("Total time for Java 8 : " + TimeUnit.NANOSECONDS.toMillis(java8Time) + "ms");
    }
}

output

Total time for Java 7 : 1001ms
Total time for Java 8 : 3232ms