Integer to String

Write a function that takes an integer as input and produces an output string.
Some sample Input/outputs are as follows
i/p o/p
1 - A
2 - B
3 - AA
4 - AB
5 - BA
6 - BB
7 - AAA
8 - AAB
9 - ABA
10 - ABB
11 - BAA
12 - BAB
13 - BBA
14 - BBB
15 - AAAA

This looks like an integer to binary conversion, however, instead of using 0, 1 representation, it would be easier to understand if we convert in this way:

A       1
B       2
AA    11
AB    12
BA    21


If we use binary representations, we will have:

A       1
B       10
AA    11
AB    110
BA    101

It is reasonable that when n % 2 = 1, we append "A". However, if n % 2 = 0, we will have one extra digit, so we need to subtract 1 before we divide by 2.

public class IntegerToString {
 public static String convert(int n){
  if(n <= 0)
   return null;
  String rst = "";
  while(n > 0){
   if((n & 1) != 0)
    rst = "A" + rst;
   else {
    rst = "B" + rst;
    n -= 1;
   }
   n = (n >> 1);
  }
  return rst;
 }
 public static void main(String[] args) {
  for(int i = 1; i <= 15; i++)
   System.out.println(convert(i));
 }
}