Write a Java program to accept a positive number and repeatedly add all its digits until the result has only one digit

import java.util.*;
public class Solution {
 public static void main(String[] args) {
  Scanner in = new Scanner(System.in);
  System.out.print("Input a positive integer: ");
  int n = in .nextInt();
  if (n > 0)
   System.out.println(add_digits_until_one(n));
 }

 public static int add_digits_until_one(int n) {
  while (n > 9) {
   int sum_digits = 0;
   while (n != 0) {
    sum_digits += n % 10;
    n /= 10;
   }
   n = sum_digits;
  }
  return n;
 }
}

Sample Output:

Input a positive integer:  25
7