java面试题 字符串安顺序写入文件

有一个字符串accceeeesd要按一定的顺序写入文件（保存到d盘的test.txt文件中）

得到的结果是：

a
ccc
d
eeee
s

package demo;import java.io.FileWriter;import java.io.IOException;import java.util.Arrays;import java.util.HashSet;import java.util.Iterator;import java.util.Set;import java.util.TreeSet;public class Test {public static void main(String[] args) {String str = "accceeeesd";sortString(str,"D:/test.txt");}public static void sortString(String str,String path){char[] ch = str.toCharArray();Set<Character> chs = new TreeSet<Character>();for (int i = 0; i < ch.length; i++) {chs.add(ch[i]);}Iterator<Character> ia = chs.iterator();FileWriter w = null;try {w = new FileWriter(path);while(ia.hasNext()){char c =  ia.next();for (int i = 0; i < ch.length; i++) {if(c==ch[i]){System.out.print(c);w.write(c);}}System.out.println();w.write("\r\n");}} catch (IOException e) {e.printStackTrace();}}}