字符串中出现次数最多的字符

public class Test3 {
    public static void main(String[] args) {
        String s = "aabasfdffffffffssf";
        int count = 0;
        String str = "";
        String res = "";
        int length = s.length(); 

        while(s.length() > 0) {
            str = String.valueOf(s.charAt(0));
            s = s.replace(str, "");
            if (count < length - s.length()) {
                count = length - s.length();
                res = str;
            }
            length = length - count;
        }
        System.out.println(res);
    }
}