static int anagram(String s) { int result = 0; Map map = new HashMap();

    if (s.length() % 2 != 0) {
        return -1;
    } else {
        int half = s.length() / 2;
        for (int k = 0; k < half; k++) {
            char letter = s.charAt(k);

            if (!map.containsKey(letter)) {
                map.put(letter, 1);
            } else {
                Integer frequency = map.get(letter);
                map.put(letter, ++frequency);
            }
        }

        for (Map.Entry<Character, Integer> entry : map.entrySet()) {
            System.out.println(entry.getKey() + " " + entry.getValue());
        }

        for (int k = half; k < s.length(); k++) {
            char letter = s.charAt(k);
            //System.out.println("a doua jumatate este:");
            //System.out.println(letter);

            if (!map.containsKey(letter)) {
                result++;
            } else {
                Integer freq = map.get(letter);
                freq--;
                map.put(letter, freq);

            }

        }



        for (Map.Entry<Character, Integer> entry : map.entrySet()) {
            System.out.println(entry.getKey() + " " + entry.getValue());
        }

        return result;

    }
}

for String xaxbbbxx I obtain 0.

Can someone one say me why?