import java.util.Scanner;

class NullDataException extends RuntimeException {
    private String detail;

    NullDataException(String a) {
        detail = a;
    }

    @Override
    public String toString() {
        return "NullDataException[" + detail + "]";
    }
}

class MethodNullReturn extends Exception {

    private boolean detail;

    MethodNullReturn(boolean b) {
        detail = b;
    }

    @Override
    public String toString() {
        return "MethodNullReturn[" + detail + "]";
    }
}

public class Main {

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.print("Введите строку: ");
        String str = s.nextLine();
        String kek = "";
        try {
            //concat(str);
            nullIsBack(str);

        } catch (NullDataException e) {
            System.out.println("caught " + e);
        } catch (MethodNullReturn e) {
            System.out.println("caught " + e);

        }


    }

    public static void concat(String a) throws NullDataException {

        System.out.println("inside concat");
        if (a.equals("")) {
            throw new NullDataException(a);
        }
        String addstr = "hello, ";
        String newstr = addstr.concat(a);
        System.out.println(newstr);

    }

    public static Boolean nullIsBack(String a) throws MethodNullReturn {
        String rez = "";
        if (a.contains("asd")) {
            rez = a;
        } else {
            rez = null;
        }
        if (rez == null) {
            throw new MethodNullReturn(false);
        }

        return true;
    }
}