Java下用牛顿迭代法实现开方

import java.util.Scanner;

public class sqrtNewton {
    public static void main(String[] args) {
        System.out.println("请输入要开方的数：");
        Scanner input = new Scanner(System.in);
        double num = input.nextDouble();
        double e = 0.01F;
        sqrt(num, e);
        num = 2;
        e = 0.0001F;
        sqrt(num, e);
        num = 2;
        e = 0.00001F;
        sqrt(num, e);
    }
    private static double sqrt(double num, double e) {
        double gssn = num / 2;
        double e0;
        int cnt = 0;
        do {
            gssn= (gssn + num / gssn) / 2;
            e0 = gssn*gssn - num;
            cnt++;
            System.out.printf("尝试 %f, 误差: %f\n", gssn, e0);
        } while (e0 > e);

        System.out.printf("尝试 %d 次, 结果为: %f\n", cnt, gssn);
        return gssn;
    }
}