String string = "aaajjfjfjfjdkdjfkasdkz";
char[] arr = string.toCharArray();
HashMap<Character, Integer> hMap = new HashMap<>();
for (char c : arr) {
if(!hMap.containsKey(c)){
hMap.put(c, 1);
}else{
hMap.put(c, hMap.get(c)+1);
}
}
System.out.println(hMap);