用java写一个英文句子反转的方法

/**
* 要求：将一个英文句子反转， e.g. much. very you love I => I love you very much.
* 但不能使用String的库函数：split,indexOf,lastIndexOf,subString
* 
*/

package ceshi;

public class Reverse {
 public static void main(String[] args){
  String str = "much.                  very you love I";
  System.out.println(reverse(str));
  
 }
 
 public static String reverse(String s){
        int pos=0;
        StringBuilder sb=new StringBuilder();
        for(int i=0;i<s.length();i++){
            char c=s.charAt(i);
            if(c==' '){
             pos=0;
            }
            sb.insert(pos, c);
            if(c!=' '){
             pos++;
            }
        }
        return sb.toString();
    }
}