557. reverse words in a string iii

class  {
    public String reverseWords(String s) {
         if (s == null || s.length() == 0) return s;
       String[] strs = s.split(" ");
        StringBuilder sb = new StringBuilder();
        for (int j = 0; j < strs.length; j++) {
         String str = strs[j];
             String st = "";
         for (int i = str.length() - 1; i >= 0; i--) {
               st += str.charAt(i);
         }
            strs[j] = st;
            if (j != strs.length - 1) {
             
             sb.append(strs[j] + " ");
            } else {
                sb.append(strs[j]);
          }
        }
        return sb.toString();
    }
}