字符串空值替换

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 sti = str.toString();

char[] strChar = sti.toCharArray();

StringBuffer stb = new StringBuffer();

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

if(strChar[i]==' '){

stb.append("%20");

}else{

stb.append(strChar[i]);

}

}

return stb.toString();

}

public static void main(String[] args) {

Solution ss=new Solution();

System.out.println(ss.replaceSpace(new StringBuffer("We Are Happy")));

}

}