public class StringFilter {
    public static String stringFilter(String input) {
        boolean[] bools = new boolean[26];
        for (int i = 0; i < bools.length; i++) {
            bools[i] = false;
}
        if (input != null && input.length() > 1) {
            StringBuilder sb = new 
 
StringBuilder();
            for (int i = 0; i < input.length(); i++) {
                char c = input.charAt(i);
                if (!bools[c]) {
                    sb.append(c);
bools[c] = true;
}
            }
            return sb.toString();
}
        return input;
}
}