import java.util.Random;
import java.security.SecureRandom;

public class TestR
{
  public static void main(String[] args)
  {
    final long count = 10000; // Total numbers
    double r1 = 0, r2 = 0, r3 = 0, r4 = 0, r5 = 0;
    double sum1 = 0, sum2 = 0, sum3 = 0, sum4 = 0, sum5 = 0;
    double sqSum1 = 0, sqSum2 = 0, sqSum3 = 0, sqSum4 = 0, sqSum5 = 0; // sum of squares
    Random r = new Random();
    SecureRandom sr = new SecureRandom();

    // Create numbers, find its sum, and its square sum
    for (long i=0; i<count; i++)
    {
      r1 = Math.random();
      r2 = r.nextDouble();
      r3 = r.nextGaussian();
      r4 = sr.nextDouble();
      r5 = sr.nextGaussian();

      sum1 += r1;
      sum2 += r2;
      sum3 += r3;
      sum4 += r4;
      sum5 += r5;

      sqSum1 += Math.pow(r1, 2);
      sqSum2 += Math.pow(r2, 2);
      sqSum3 += Math.pow(r3, 2);
      sqSum4 += Math.pow(r4, 2);
      sqSum5 += Math.pow(r5, 2);
    }

    // Find mean
    double mean1 = sum1/count;
    double mean2 = sum2/count;
    double mean3 = sum3/count;
    double mean4 = sum4/count;
    double mean5 = sum5/count;

    // Find standard deviation, without using an array to store all the numbers
    double deviation1 = Math.sqrt((sqSum1 - sum1*sum1/count)/(count - 1));
    double deviation2 = Math.sqrt((sqSum2 - sum2*sum2/count)/(count - 1));
    double deviation3 = Math.sqrt((sqSum3 - sum3*sum3/count)/(count - 1));
    double deviation4 = Math.sqrt((sqSum4 - sum4*sum4/count)/(count - 1));
    double deviation5 = Math.sqrt((sqSum5 - sum5*sum5/count)/(count - 1));

    // Display result
    System.out.println("The mean using Math.random is " + mean1);
    System.out.println("    STD is " + deviation1);
    System.out.println("The mean using Random class is " + mean2);
    System.out.println("    STD is " + deviation2);
    System.out.println("The mean of Gaussian numbers using Random is " + mean3);
    System.out.println("    STD is " + deviation3);
    System.out.println("The mean using SecureRandom is " + mean4);
    System.out.println("    STD is " + deviation4);
    System.out.println("The mean of Gaussian numbers using SecureRandom is " + mean5);
    System.out.println("    STD is " + deviation5);
  }
}