Finding Square root without using sqrt function in java

public class Maths {

      public double sqrt(double number) {

            if (number < 0) {

                  return Double.NaN;

            }

            if (number == 0) {

                  return number;

            }

            double epsilon = 1e-15;

            double root = 0;

            double sqrt = number;

            while (Math.abs(sqrt - (root = (number / sqrt))) > epsilon * sqrt) {

                  sqrt = (root + sqrt) / 2.0;

            }

            return sqrt;

      }

      public static void main(String[] args) {

            double num = 2;

            Maths m = new Maths();

            double sqrt = m.sqrt(num);

            System.out.println("SQRT is " + sqrt);

      }

}