面试题：统计单词中各个字母出现的次数？该如何解决

/**     * 检索一段字符串中每个字符出现的次数     * @param args     * @return     */    public static Map<Character, Integer> charNonu(char args[]) {        Map<Character, Integer> map = new TreeMap<Character, Integer>();        for(int i = 0; i < args.length; i++) {            char temp = args[i];            if(!map.containsKey(temp)) {                map.put(temp, 1);            }else {                int auto = map.get(temp)+1;                map.put(temp, auto);            }        }        return map;    }
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Java code
package com.studjava;import java.util.ArrayList;import java.util.List;public class Test11 {    /**   * @param args   */    public static void main(String[] args) {        String a = "abcdBbefgaAAA";       //a = a.toLowerCase() ;  //如果要统计不区分大小写的话 ，就统一转换为小写或者大写     int [] ii = new int[256] ;     List list = new ArrayList() ;     char[] cs = a.toCharArray();        for (char c : cs) {            if (ii[c] == 0){             list.add(c) ;         }         ii[c] =  ii[c] + 1;        }            char ch ;     for (int i = 0; i < list.size(); i++){         ch = (Character) list.get(i) ;         System.out.println(ch + "  出现次数： " + ii[ch]) ;     } }   }