统计一个字符串中出现次数最多的字符

public void countCharacterInString(){  
    String target = "hello world  what about you today";  
    //将包含的字符放入哈希表，字符作为key，出现次数作为value  
    char[] alph = target.toCharArray();  
    Map<Character,Integer> aa = new HashMap<Character,Integer>();  
    for(Character c:alph){  
        if(Character.isWhitespace(c)) continue;  
        if(aa.containsKey(c) == false){  
             aa.put(c, 1);  
         }else{  
             aa.put(c, aa.get(c)+1);  
         }  
    }  
    //比较获取出现最多次数的字符  
    Set<Character> set = aa.keySet();  
    Iterator iter = set.iterator();  
    Integer count=0;  
    Character key = new Character(' ');  
      
    while(iter.hasNext()){  
        Character ccc = (Character)iter.next();  
        System.out.println(ccc +": "+ aa.get(ccc));  
        if(aa.get(ccc) > count){  
            count = aa.get(ccc);  
            key = ccc;  
        }  
    }  
      
    System.out.println(key.toString()+" "+ count);  
}