public class Controller {

    @FXML
    AnchorPane signInPane;

    @FXML
    private TextField usernameForSignIn;

    @FXML
    private PasswordField password;

    @FXML
    private Button signIn;

    @FXML
    private Button registration;

    @FXML
    void initialize() {
        registration.setOnAction(event -> {
            signInPane.setVisible(false);
            SignUpController.registerPane.setVisible(true);
        });

        signIn.setOnAction(event ->  {
            String usernameText = usernameForSignIn.getText().trim();
            String passwordText = password.getText().trim();

            if(!usernameText.equals("") && !passwordText.equals("")) {
                loginUser(usernameText, passwordText);
            } else {
                System.out.println("Empty login and/or password");
            }

        });
    }

    private void loginUser(String usernameText, String passwordText) {
    }

}

public class SignUpController {

    @FXML
    static AnchorPane registerPane;

    @FXML
    private TextField email;

    @FXML
    private PasswordField pass;

    @FXML
    private Button signUp;

    @FXML
    private TextField fname;

    @FXML
    private TextField lname;

    @FXML
    private TextField username;

    @FXML
    private RadioButton radioMale;

    @FXML
    void initialize() {

        signUp.setOnAction(event -> {

            signUpNewUser();

        });
    }

    private void signUpNewUser() {
        DatabaseHandler databaseHandler = new DatabaseHandler();

        String firstName = fname.getText();
        String lastName = lname.getText();
        String usname = username.getText();
        String password = pass.getText();
        String e_mail =  email.getText();
        String gender = "";
        if(radioMale.isSelected()) {
            gender = "Male";
        } else {
            gender = "Female";
        }

        User user = new User(firstName,lastName,usname,password,e_mail,gender);

        databaseHandler.signUpUser(user);

    }
}

registration.setOnAction(event -> {
            registration.getScene().getWindow().hide();

            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(getClass().getResource("/sample/view/signUp.fxml"));

            try {
                loader.load();
            } catch (IOException e) {
                e.printStackTrace();
            }

            Parent root = loader.getRoot();
            Stage stage = new Stage();
            stage.setScene(new Scene(root));
            stage.showAndWait();

//            signInPane.setVisible(false);
        });