JavaSe 统计字符串中字符出现的次数

    public static void main(String[] args) {
        // 1、字符串
        String str = "*Constructs a new <tt>HashMap</tt> with the same mappings as the *  specified <tt>Map</tt>. The<tt>HashMap</tt> is created with default load factor (0.75) and aninitial capacity sufficient to*hold the mappings in the specified<tt>Map</tt>.";
        // 2.把字符串转换为数组
        char[] charArr = str.toCharArray();
        // 3.创建一个Map
        Map<Character, Integer> counterMap = new HashMap<Character, Integer>();
        // 4.遍历一个Map
        for (int i = 0; i < charArr.length; i++) {
            // 5.拿到的字符作为键到集合中去找值
            Integer value = counterMap.get(charArr[i]);
            if (value == null) {
                // 把字符作为键，1为值存入集合
                counterMap.put(charArr[i], 1);
            } else {
                // 把值加1重新写入集合
                value += 1;
                counterMap.put(charArr[i], value);
            }
        }
        Set<Map.Entry<Character, Integer>> entrySet = counterMap.entrySet();
        for (Map.Entry<Character, Integer> entry : entrySet) {
            System.out.println(entry.getKey() + " 字符出现次数=" + entry.getValue());
        }
    }