替换空格

public class Solution { 
    public String replaceSpace(StringBuffer str) { 
        StringBuffer result = new StringBuffer(str.length() * 3); 
        for (int i = 0; i < str.length(); i++){ 
            char c = str.charAt(i); 
            if(' ' == c){ 
                result.append("%20"); 
            }else{ 
                result.append(c); 
            } 
        } 
        return result.toString(); 
    } 
}