String/StringBuffer

public class ReplaceBlank {
    public static void main(String[] args) {
        String str="i am happy";
        str=replaceBlank(str);
        System.out.println(str);
    }
    
    
    public static String replaceBlank(String str){
        if(null==str){
            return null;
        }
        StringBuffer sb=new StringBuffer();
        for(int i=0;i<str.length();i++){
            if(str.charAt(i)==‘ ‘){
                sb.append("%20");
            }else{
                sb.append(str.charAt(i));
            }
        }
        return sb.toString();
    }

}