Base 7

 1 public class Solution {
 2     public String convertToBase7(int num) {
 3         if (num == 0) return "0";
 4         
 5         StringBuffer result = new StringBuffer();
 6         Boolean isNegative = false;
 7         if (num < 0) {
 8             isNegative = true;
 9             num = -num;
10         }
11         
12         while (num != 0) {
13             int insertMe = num % 7;
14             result.insert(0, Integer.toString(insertMe));
15             num /= 7;
16         }
17         if (isNegative) result.insert(0, "-");
18         return result.toString();
19     }
20 }

 1 public class Solution {
 2     public String convertToBase7(int num) {
 3         if (num == 0) return "0";
 4         
 5         Boolean isNegative = num < 0;
 6         num = Math.abs(num);
 7         
 8         String result = "";
 9         while (num != 0) {
10             result = Integer.toString(num % 7) + result;
11             num /= 7;
12         }
13         return isNegative ? "-" + result : result;
14     }
15 }