왜 컴파일 에러가 뜰까요 .. ㅠ

public class Main{

public String solution(int num, String str) {

String answer = "";

for (int i=0; i<num; i++ ) {

String tmp = str.substring(0, 7).replace('#', '1').replace('*', '0');

answer += Character.toString(Integer.valueOf(tmp, 2));

str = str.substring(7);

}

return answer;

}

public static void main(String[] args) {

Main T = new Main();

Scanner scr = new Scanner(System.in);

int num = scr.nextInt();

String str = scr.next();

System.out.println(T.solution(num, str));

}

}