HashMap<Character, Integer> dict = new HashMap<>();
char[] chars = "AXyyXyZy+9-+b; b!+a++9++1991".toCharArray();
for (char letter : chars) dict.put(letter, dict.containsKey(letter) ? dict.get(letter) + 1 : 1);
for (Character i : dict.keySet()) System.out.printf(Character.isLetterOrDigit(i) ? "key: '%s' value: %s\n" : "", i, dict.get(i));