Split vs. Substring

import java.util.ArrayList;
import java.util.List;

public class SplitStringEvery {
    private static final int numberOfRepeats = 3000000;
    private static final String textToRepeat = "1";
    private static final int interval = 1;
    private static final int numberOfTestsToRun = 10;

    public static void main(String[] args) {
        StringBuilder sb = new StringBuilder(numberOfRepeats * textToRepeat.length());

        for (int i = 0; i < numberOfRepeats; i++) {
            sb.append(textToRepeat);
        }
        final String stringToSplit = sb.toString();

        List<Long> elapsedTimesSplit =  new ArrayList<Long>(numberOfTestsToRun);
        List<Long> elapsedTimesSubstring =  new ArrayList<Long>(numberOfTestsToRun);

        long startTime;
        long endTime;


        //Tests to run
        for (int i = 0; i < numberOfTestsToRun; i++) {
            startTime = System.currentTimeMillis();
            stringToSplit.split("(?<=\\G.{" + interval + "})");
            endTime = System.currentTimeMillis();
            elapsedTimesSplit.add(endTime - startTime);

            //-------------

            startTime = System.currentTimeMillis();
            splitStringEvery(stringToSplit, interval);
            endTime = System.currentTimeMillis();
            elapsedTimesSubstring.add(endTime - startTime);
        }

        //Calculate averages:

        long splitSum = 0;
        long substringSum = 0;
        for (int i = 0; i < numberOfTestsToRun; i++) {
            splitSum += elapsedTimesSplit.get(i);
            substringSum += elapsedTimesSubstring.get(i);
        }

        long splitAvg = splitSum / elapsedTimesSplit.size();
        long substringAvg = substringSum / elapsedTimesSplit.size();

        //Print data:
        System.out.println("Split:");
        System.out.println(elapsedTimesSplit);

        System.out.println("Substring:");
        System.out.println(elapsedTimesSubstring);

        System.out.println("\nAverage:");
        System.out.println("Split: " + splitAvg + " Substring: " + substringAvg);

        System.out.println("\nFactor:");
        System.out.println(splitAvg / (double)substringAvg);
    }

    public static String[] splitStringEvery(String s, int interval) {
        int arrayLength = (int) Math.ceil(((s.length() / (double)interval)));
        String[] result = new String[arrayLength];

        int j = 0;
        int lastIndex = result.length - 1;
        for (int i = 0; i < lastIndex; i++) {
            result[i] = s.substring(j, j + interval);
            j += interval;
        }
        result[lastIndex] = s.substring(j);

        return result;
    }
}