You should be able to do it using something like this:
String orig = "some crap to sort";
char[] chArr = new char[orig.size()]; //new char array of same length as string
orig.getChars(0, orig.length()-1, chArr, 0); //place characters of string into char array
Arrays.sort(chArr); //sort the array
String sorted = new String(chArr); //make a new string to hold the sorted characters
you might also be able to use Strings getBytes() method and then cast that to a char[] to sort, not sure which way is better.