leetcode 504. Base 7

public class Solution {    public String convertToBase7(int num) {        if (num == 0)     return "0";    String res = "";    int temp = num;    int remainder =  temp % 7;    while (temp!=0) {    res = String.valueOf(Math.abs(remainder)) + res;    temp /= 7;    remainder = temp % 7;    }        if (num < 0 )     res = "-" + res;    return res;    }}