求字符串中每个字符出现的次数

1.

    //从字符串中获取每个字符出现的次数
    private static String getCharCount(String str) {
        //1. 将字符串转换成字符数组
        char[] chars = str.toCharArray();
        //2.
        Map<Character, Integer> map = new TreeMap<Character, Integer>();
        for (int i = 0; i < chars.length; i++){
            if (!(chars[i] >= 'a'&& chars[i] <='z' || chars[i] >= 'A'&& chars[i] <='Z')){//如果不是字母则继续遍历
                continue;
            }
            //将数组中的字母作为key去查map表
           Integer  value = map.get(chars[i]);
           int count = 1;
            if (value != null){
                count = value + 1;
            }
            map.put(chars[i],count);
        }
        return  mapToString(map);
    }

    private static String mapToString(Map<Character, Integer> map) {
        StringBuilder sb = new StringBuilder();
        Iterator<Character> it = map.keySet().iterator();
        while (it.hasNext()){
            Character key = it.next();
            Integer value = map.get(key);
            sb.append(key+"("+value+")");
        }
        return  sb.toString();
    }