public static final String getLowerCaseString(int index) 
{
		return getString(index);
}

Translates a positive integer (not equal to zero) into a String using the letters 'a' to 'z'; 1 = a, 2 = b, ..., 26 = z, 27 = aa, 28 = ab,...

 public static final String getString(int index) 
{
    	if (index <  1) throw new NumberFormatException(
    			"You can't translate a negative number into an alphabetical value.");
    	index--;
    	int bytes = 1;
    	int start = 0;
    	int symbols = 26;  
    	while(index  >= symbols + start) {
    		bytes++;
    	    start += symbols;
    		symbols *= 26;
    	}
    	int c = index - start;
    	char[] value = new char[bytes];
    	while(bytes  > 0) {
    		value[--bytes] = (char)( 'a" + (c % 26));
    		c /= 26;
    	}
    	return new String(value);
}

Translates a positive integer (not equal to zero) into a String using the letters 'a' to 'z'; 1 = a, 2 = b, ..., 26 = z, 27 = aa, 28 = ab,...

 public static final String getString(int index,
    boolean lowercase) 
{
		if (lowercase) {
			return getLowerCaseString(index);
		}
		else {
			return getUpperCaseString(index);
		}
}

Translates a positive integer (not equal to zero) into a String using the letters 'a' to 'z' (a = 1, b = 2, ..., z = 26, aa = 27, ab = 28,...).

 public static final String getUpperCaseString(int index) 
{
		return getString(index).toUpperCase();
}

Translates a positive integer (not equal to zero) into a String using the letters 'A' to 'Z'; 1 = A, 2 = B, ..., 26 = Z, 27 = AA, 28 = AB,...

 public static  void main(String[] args) 
{
		for (int i = 1; i <  32000; i++) {
			System.out.println(getString(i));
		}
}

Test this class using this main method.