keepCountOfCharactersInString.java

public void keepCountOfCharactersInString(String str) {

  HashMap<Character, Integer> map = new HashMap<>();

  for (int i = 0; i < str.length(); i++) {
    if (!map.containsKey(str.charAt(i)) {
        map.put(str.charAt(i), 1);
    } else {
        int currentCount = map.get(str.charAt(i));
        currentCount++;
        map.put(str.charAt(i), currentCount);
    }
  }
  
}