Sum of Digits / Digital Root

In this kata, you must create a digital root function.

A digital root is the recursive sum of all the digits in a number. Given n, take the sum of the digits of n. If that value has two digits, continue reducing in this way until a single-digit number is produced. This is only applicable to the natural numbers.

Here's how it works (Ruby example given):

digital_root(16)
=> 1 + 6
=> 7

digital_root(942)
=> 9 + 4 + 2
=> 15 ...
=> 1 + 5
=> 6

digital_root(132189)
=> 1 + 3 + 2 + 1 + 8 + 9
=> 24 ...
=> 2 + 4
=> 6

digital_root(493193)
=> 4 + 9 + 3 + 1 + 9 + 3
=> 29 ...
=> 2 + 9
=> 11 ...
=> 1 + 1
=> 2

Good Solution1:

public class DRoot {
  public static int digital_root(int n) {
    return (n != 0 && n%9 == 0) ? 9 : n % 9;
  }
}

Good Solution2:

public class DRoot {
  public static int digital_root(int n) {
    while(n > 9){
      n = n/10 + n % 10;
      }
    return(n);
  }
}