如何使用Java语言把一个英文句子以堆栈结构实现倒序输出每个单词的字符

import java.util.*;
public class TestDaoxu {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
String s = TestDaoxu.daoxu("hello world !");
System.out.println("s = " + s);
}
public static String daoxu(String str){
String s = "";
Stack sk = new Stack();
char[] ch = str.toCharArray();
s = "";
for(int i = 0;i < ch.length;i ++){
sk.push(ch[i]);
}
for(int i = 0;i < ch.length;i ++){
ch[i] = (Character)sk.pop();
s = s + ch[i];
}
return s;
}
}