请实现一个函数，将一个字符串中的空格替换成“%20”。例如，当字符串为We Are Happy.则经过替换之后的字符串为We%20Are%20Happy。

 public class Solution {

     public String replaceSpace(StringBuffer str){

         String strTemp = "";

         for(int i = 0; i < str.length(); i++){

             if(str.charAt(i) == ' '){

                 strTemp += "%20";

                 continue;

             }

             strTemp += str.charAt(i);

         }

         return strTemp;

     }

     public static void main(String[] args) {

         Solution solutionBlank = new Solution();

         StringBuffer str = new StringBuffer("We Are Happy");

         System.out.println(solutionBlank.replaceSpace(str));

     }

 }