calculate Standard Deviation in java

/**
 * @author lautturi.com
 * Java example: calculate Standard Deviation of numbers in java
 */

import java.util.*;
import java.time.*;

public class Lautturi {

	public static double calculateStdDeviation(double numArray[])
    {
        double sum = 0.0, standardDeviation = 0.0;
        int length = numArray.length;

        for(double num : numArray) {
            sum += num;
        }

        double mean = sum/length;

        for(double num: numArray) {
            standardDeviation += Math.pow(num - mean, 2);
        }

        return Math.sqrt(standardDeviation/length);
    }
	
	public static void main(String[] args) {
		double[] arr = { 1,4,2,7,5,16,12,8,13,28 };
		double stddev = calculateStdDeviation(arr);

        System.out.format("Standard Deviation = %.6f", stddev);
	}

}

output:

Standard Deviation = 7.683749