"Welcome, null" but I want to see Welcome, {nameOfLoggedInUser}

Question

I am creating a Library System using JavaFX where you can lend items to the members. I've created a login that takes me to another fxml file called main-view.fxml which has a controller called MainWindowController.

The problem I have is that after successful login, the new Window/Scene displays "Welcome, null" but what I expect the program to do is welcome the logged-in user by his username.

A screenshot to show how the main window looks and the problem I am trying to solve can be found below. I want it to Welcome the user by its name. I have used welcomeLabel.SetText(); to get username by getter getUsername(); from User class.

I believe I get null because the data when we log in is not carried forward to the next scene. I am not sure how to do that. Hope I have explained the problem well. I have searched about this a lot on this platform but could not find an answer that completely solves my worries.

I have pasted the code for MainWindowController, LoginController, User class, and a hardcoded Database. Thank you in advance.

A screenshot of main window](https://i.stack.imgur.com/fMXp7.png)

The Login controller class:

public class LoginController {

    @FXML
    private Label loginStatus;
    @FXML
    private TextField usernameField;
    @FXML
    private TextField passwordField;
    @FXML
    private Button loginButton;
    Database database;

    public LoginController() {}

    @FXML
    public void onLoginButtonClicked(ActionEvent actionEvent) throws IOException {
        database = new Database();
            for (User user : database.getUsers()) {
                if (usernameField.getText().equals(user.getUsername()) &&
                        (passwordField.getText().equals(user.getPassword()))) {

                        Stage loginStage = (Stage) loginButton.getScene().getWindow();
                        loginStage.close();

                        MainWindowController mainWindowController = new MainWindowController();
                        mainWindowController.loadScene("main-view.fxml");

                } else if (usernameField.getText().isEmpty() && passwordField.getText().isEmpty()) {
                    loginStatus.setText("Please enter your username and password.");
                } else {
                    loginStatus.setText("Wrong credentials, please try again.");
                }
            }
    }
}

The MainWindow controller class:

public class MainWindowController implements Initializable {


    Database database;
    User loggedUser;

    public MainWindowController() {}

    @Override
    public void initialize(URL url, ResourceBundle resourceBundle) {
        database = new Database();
        loggedUser = new User();
        lblWelcome.setText("Welcome, " + loggedUser.getUsername());
    }

    static public void loadScene(String name) throws IOException {
        FXMLLoader fxmlLoader = new FXMLLoader(HelloApplication.class.getResource(name));

        Stage stage = new Stage();
        Scene scene = new Scene(fxmlLoader.load());
        stage.setTitle("Lending/Receiving   - Library System");
        stage.setScene(scene);
        stage.showAndWait();
    }
}

The User class:

public class User {

    private String username;
    private String password;

    public User(){ }

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) { this.username = username; }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {this.password = password; }

}

The database class, just in case, it is needed:

public class Database {

    private List<User> users = new ArrayList<>();

    public List<User> getUsers() { return users; }

    public Database() {

        //users
        users.add(new User("u", "p"));
        users.add(new User("admin", "admin"));

    }
}