输入一串字符串，统计各个字符出现的次数

public class StatisticZEN {
    public static void main(String[] args) {
        String str = "中国aadf的111萨bbb菲的zz萨菲";
        showFrequency(str);

    private static HashMap<Character, Integer> showFrequency(String str) {
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        for (int i = 0; i < str.length(); i++) {
            char c = str.charAt(i);
            Integer num = map.get(c);
            if(num == null)
                num = 1;
            else
                num ++;
            map.put(c,num);
        }
        return map;
    }
}

 统计文章中某个单词出现的频率

public class FrequencyOfWords {
    public static void main(String[] args) throws Exception {
        System.out.println(frequencyOfWords("student"));
        System.exit(0);
    }
    public static int frequencyOfWords(String string) throws Exception{
        File file = new File("C:\\Users\\刘新成\\Desktop\\English.txt");
        FileReader fr = new FileReader(file);
        char[] chars = new char[(int)file.length()];
        fr.read(chars);
        String txt = String.valueOf(chars);
        String[] arr = txt.split("\\W+");
        Map<String,Integer> map = new HashMap<String,Integer>();
        for (String str : arr) {
            Integer frequency = map.get(str);
            if(frequency==null)
                frequency=1;
            else
                frequency++;
            map.put(str, frequency);
        }
        return map.get(string);
    }
}