Java实现：请实现一个函数，将一个字符串中的每个空格替换成"%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。

 1 import java.util.Scanner;
 2 
 3 public class Solution {
 4     public static void main(String[] args) {
 5         Scanner scanner = new Scanner(System.in);
 6         StringBuffer str = new StringBuffer(scanner.nextLine());
 7         String result = replaceSpace(str);
 8         System.out.println(result);
 9     }
10     public static String replaceSpace(StringBuffer str) {
11         for(int i=0 ; i<str.length() ; i++) {
12             if(str.charAt(i) == ' ') {
13                 str.replace(i,i+1, "%20");
14             }
15         }
16         return str.toString();
17     }
18 }