1 public class Solution {
 2     public String replaceSpace(StringBuffer str) {
 3         int startIndex;
 4         while((startIndex = str.indexOf(" ")) >= 0){
 5             str.replace(startIndex, startIndex + 1, "%20");
 6         }
 7         System.out.println(str);
 8         return str.toString();
 9     }
10 }