reverse letters keep numbers in place in java

1public class Challenge {
2	public static String reverse(String str) {
3	  	char[] c = str.toCharArray();
4      int i = 0, j = c.length-1;
5		  while(i< j){
6				while(Character.isDigit(c[i]))
7					i++;
8        while(Character.isDigit(c[j]))
9					j--;
10        char t = c[i];
11        c[i] = c[j];
12				c[j] = t;
13        i++;
14				j--;
15				
16			} 
17		return new String(c);
18 
19
20	}
21}