java:当字符串为We Are Happy.经过替换之后的字符串为We%20Are%20Happy

方法一：

public class Solution {
    public String replaceSpace(StringBuffer str) {
     String a=str.toString();
          char[] b = a.toCharArray();
          StringBuilder sBuilder = new StringBuilder();
          for (char c : b) {
              if(c==' ') {
              sBuilder.append("%20");
              }else {
                 sBuilder.append(c);
            }
        }
         String e = sBuilder.toString();
         return e;

    }
}