class NaturalComparator implements Comparator {  // use generic objects and .toString() to support File etc
    public int compare(Object f1, Object f2) {
        // split *between* the transition from digits to non-digits & vice-versa
        String[] s1 = f1.toString().split("(?<!\\d)(?=\\d)|(?<=\\d)(?!\\d)");
        String[] s2 = f2.toString().split("(?<!\\d)(?=\\d)|(?<=\\d)(?!\\d)");
        int c = 0;
        for (int i = 0; i < s1.length && i < s2.length; i++)
        {
            // there are non-digits or the digits are the same length
            if (s1[i].length() == s2[i].length() || s1[i].matches("\\D") || s2[i].matches("\\D"))
                c = s1[i].compareTo(s2[i]);
            else
                c = s1[i].length() > s2[i].length() ? 1 : -1;
            if (c != 0)
                return c;
        }
        return s1.length == s2.length ? 0 : s1.length > s2.length ? 1 : -1;
    }
}