add digits

Given an integer num, repeatedly add all its digits until the result has only one digit, and return it.
Example 1:

Input: num = 38
Output: 2
Explanation: The process is
38 --> 3 + 8 --> 11
11 --> 1 + 1 --> 2 
Since 2 has only one digit, return it.
Example 2:

Input: num = 0
Output: 0

class Solution {
    public int addDigits(int num) {
        if(num==0){
            return 0;
        }
        if(num%9==0){
            return 9;
        }
        return(num %9);
    }
}