Java unknown error

[NeroMn-ExE]

Hello i got some issue with it
i been start coding for 3 months and im using BlueJ
im trying to write simple online bank code with a login,registering and saving there datas with it.
this is my code( i got help from chatgpt for adding interface function):

import javax.swing.;
import java.awt.;
import java.awt.event.;
import java.io.;
import java.util.Scanner;

public class Burtgel extends JFrame implements ActionListener {
public static final String USER_FILENAME = "Hereglegch.ser";
public static final String ACCOUNT_FILENAME = "Account.ser";
private static final int FRAME_WIDTH = 300;
private static final int FRAME_HEIGHT = 200;
private static final int FRAME_X_ORIGIN = 150;
private static final int FRAME_Y_ORIGIN = 250;
private JButton cancelButton;
private JButton okButton;
private JTextField inputLine;
private JLabel prompt;

public Burtgel() {
    Container contentPane = getContentPane();
    contentPane.setLayout(new FlowLayout());

    prompt = new JLabel("Нэр: "); // Initializing prompt with a default text
    contentPane.add(prompt);

    inputLine = new JTextField(20);
    contentPane.add(inputLine);
    inputLine.addActionListener(this);

    okButton = new JButton("OK");
    contentPane.add(okButton);
    cancelButton = new JButton("CANCEL");
    contentPane.add(cancelButton);

    cancelButton.addActionListener(this);
    okButton.addActionListener(this);

    setDefaultCloseOperation(EXIT_ON_CLOSE);
}

public void actionPerformed(ActionEvent e) {
    if (e.getSource() == cancelButton) {
        // Handle cancel button click
        // For example, close the window
        dispose();
    } else if (e.getSource() == okButton || e.getSource() == inputLine) {
        // Handle OK button click or Enter key press in the input field
        String userInput = inputLine.getText();
        // Process the user input further
    }
}

public static void main(String[] args) {
    // Assuming you want to call either login or register based on some condition
    // Replace the condition with your logic
    boolean isLoggedIn = false; // Set it to true if the user is already logged in
    if (isLoggedIn) {
        login();
    } else {
        register();
    }
}

public static void register() {
    try (Scanner scanner = new Scanner(System.in)) {
        JFrame frame = new Burtgel();
        frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
        frame.setResizable(false);
        frame.setTitle("Registration");
        frame.setLocation(FRAME_X_ORIGIN, FRAME_Y_ORIGIN);
        frame.setVisible(true);
    } catch (Exception ex) {
        ex.printStackTrace();
    }
}

public static void login() {
try (Scanner scanner = new Scanner(System.in);
FileInputStream userFileIn = new FileInputStream(USER_FILENAME);
ObjectInputStream userIn = new ObjectInputStream(userFileIn);
FileInputStream haygFileIn = new FileInputStream(ACCOUNT_FILENAME);
ObjectInputStream haygIn = new ObjectInputStream(haygFileIn)) {

    JFrame frame = new Burtgel();
    frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
    frame.setResizable(false);
    frame.setTitle("Login");
    frame.setLocation(FRAME_X_ORIGIN, FRAME_Y_ORIGIN);

    Container contentPane = frame.getContentPane();
    contentPane.setLayout(new FlowLayout());

    JLabel prompt = new JLabel("Нэр: ");
    contentPane.add(prompt);

    Hereglegch user = (Hereglegch) userIn.readObject();
    Account hayg = (Account) haygIn.readObject();

    String username = scanner.nextLine();

    if (!user.getName().equals(username)) {
        prompt.setText("Хэрэглэгч олдсонгүй.");
        return;
    }

    JLabel prompt2 = new JLabel("Нууц үг: ");
    contentPane.add(prompt2);
    String password = scanner.nextLine();

    if (!user.getPassword().equals(password)) {
        prompt.setText("Нууц үг буруу байна.");
        return;
    }

    prompt.setText("Амжилттай нэвтэрлээ");
    Balance balance = new Balance(hayg);
    frame.setVisible(true);
    Undsen.displayInfo(hayg, balance);

} catch (IOException | ClassNotFoundException ex) {
    ex.printStackTrace();
}

}
}

oftenly my coding programm shows me where i got wronged but this time it says:
Error(s) found in class. Press Ctrl+K or click right to go to next error.
And doesnt show me where i got mistake, i have no idea about where i lost.