【简单】字符串字母数统计

public static String charCount(String str) {
            String res = "";
            Map<String, Integer> map = new HashMap<>();
            char[] charArr = str.toCharArray();
            for(char c : charArr){
                if((c >=‘a‘&& c < ‘z‘)|| (c>=‘A‘ && c <= ‘Z‘)){
                    String key = String.valueOf(c);
                    if(map.containsKey(key)){
                        map.put(key,map.get(key) + 1);
                    }else{
                        map.put(key,1);
                    }
                }else{
                    continue;
                }
            }
            List<String> strList = new ArrayList<String>();
            strList.addAll(map.keySet());
            Collections.sort(strList);
            for(String charStr : strList){
                res += charStr + map.get(charStr);
            }
            return res;
        }
        public static void main(String[] args){
            System.out.println(charCount("AAABBC"));
            System.out.println(charCount("A"));
            System.out.println(charCount("AA"));
            System.out.println(charCount("ABC"));
            System.out.println(charCount("AA55AdfereadfB44BC4"));
        }