Why doesn't the window controller see the list from the main class?

Question

Avocode

Generally. Such situation.
I pass from the main class to the class-controller of the settings window a list with the values ​​​​set earlier in the main class through the constructor. Here is the main class code:

public class MainClass extends Application {
  
  private Stage primaryStage;
  private BorderPane rootLayout;
  private Settings settings;
  
  
  @Override
  public void start(Stage primaryStage) {
    this.primaryStage = primaryStage;
    this.primaryStage.setTitle("Антикафе");
    
    initRootLayout();
    showPersonOverview();
  }
  
   private ObservableList<Settings> Data = FXCollections.observableArrayList();
  
  public MainClass() {
    Data.add(new Settings(false,false,false,false));
  }
  
  public ObservableList<Settings> getData() {
        return Data;
    }
   public boolean showSettingsDialog() {
        try {
            // Загружаем fxml-файл и создаём новую сцену
            // для всплывающего диалогового окна.
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(MainClass.class.getResource("view/settings.fxml"));
            AnchorPane page = (AnchorPane) loader.load();

            // Создаём диалоговое окно Stage.
            Stage dialogStage = new Stage();
            dialogStage.setTitle("Настройки");
            dialogStage.initModality(Modality.WINDOW_MODAL);
            dialogStage.initOwner(primaryStage);
            Scene scene = new Scene(page);
            dialogStage.setScene(scene);
            
            
         // Передаём список настроек в контроллер.
            ButtonSettingsControll controller = loader.getController();
            controller.setDialogStage(dialogStage);
            controller.setData(Data);
            controller = new ButtonSettingsControll(Data);
            
            // Отображаем диалоговое окно и ждём, пока пользователь его не закроет
            dialogStage.showAndWait();
            return true;
        } catch (IOException e) {
            e.printStackTrace();
            return false;
        }
    }
}

Here is the code for the controller itself:

public class ButtonSettingsControll {
  
    private Stage dialogStage;
    @FXML
    public CheckBox checkKal;
    @FXML
    public CheckBox checkStopCheck;
    @FXML
    public CheckBox checkTea;
    @FXML
    public CheckBox checkVIP;
    @FXML
    public TextField kalHard;
    @FXML
    public TextField kalNorm;
    @FXML
    public TextField kalLight;
    @FXML
    public TextField priceTea;
    @FXML
    public TextField priceUnd;
    @FXML
    public TextField peoplsUndo;
    @FXML
    public TextField priceTo;
    @FXML
    public TextField peoplsTo;
    @FXML
    public TextField priceStopCheck;
    
    private MainClass mainClass;
    private ObservableList<Settings> Data = FXCollections.observableArrayList();
    
    public void setMain(MainClass mainClass) {
      this.mainClass = mainClass;
    }
    public void setData(ObservableList<Settings> data) {
      Data = data;
    }
    
                //Пока не разберусь со списком для наглядности буду использовать это
    Boolean CK = false;
    Boolean CT = false;
    Boolean CV = false;
    Boolean CC = false;
    
    public void setDialogStage(Stage dialogStage) {
          this.dialogStage = dialogStage;
      }
    
    public ButtonSettingsControll() {
    }
    public ButtonSettingsControll(ObservableList<Settings> data) {
      Data = data;
      System.out.println(Data.get(0).getCheckK());
      checkKal.setSelected(data.get(0).getCheckK());
      
    }
    
    @FXML
      private void initialize() {
      if(CK)
        checkKal.setSelected(true);
      else {
        checkKal.setSelected(false);
        kalHard.setDisable(true);
        kalNorm.setDisable(true);
        kalLight.setDisable(true);
      }
      if(CT)
        checkTea.setSelected(true);
      else {
        checkTea.setSelected(false);
        priceTea.setDisable(true);
      }
      if(CV)
        checkVIP.setSelected(true);
      else {
        checkVIP.setSelected(false);
        priceUnd.setDisable(true);
        priceTo.setDisable(true);
        peoplsTo.setDisable(true);
        peoplsUndo.setDisable(true);
      }
      if(CC)
        checkStopCheck.setSelected(true);
      else {
        checkStopCheck.setSelected(false);
        priceStopCheck.setDisable(true);
      }
    }
    
    @FXML
    private void settings() {
      Data.setAll(new Settings(checkKal.isSelected(),checkTea.isSelected(),checkVIP.isSelected(),checkStopCheck.isSelected()));
      System.out.println(Data.get(0).getCheckK());
          dialogStage.close();
    }
}

I can't figure out why I'm getting an exception (java.lang.NullPointerException) when I call the settings window.
The exception appears in this block:

public ButtonSettingsControll(ObservableList<Settings> data) {
      Data = data;
      System.out.println(Data.get(0).getCheckK());
      checkKal.setSelected(Data.get(0).getCheckK());
      
    }

Namely here

checkKal.setSelected(data.get(0).getCheckK());

.
The output to the console works, (done for verification), but when I try to use the same value to set the checkbox in the checkbox, the program crashes due to this exception. Plz tell me what is wrong.

Answer 1

here is an error.

// Передаём список настроек в контроллер.
            ButtonSettingsControll controller = loader.getController();
            controller.setDialogStage(dialogStage);
            controller.setData(Data);
            controller = new ButtonSettingsControll(Data);

here

ButtonSettingsControll controller = loader.getController();

received a link to the controller from the loader.
and here controller = new ButtonSettingsControll(Data);created a new object not related to the loaded FXML
And more. When the controller's constructor is called, the controls declared with the @FXML annotation have not yet been created. Therefore, such a constructor does not make sense. And the loader calls the default constructor (the one without parameters). This means that either after receiving a link from the loader to the controller, you call its setData method and anything else and fill in the data controls. Or you create a controller and pass a reference to it to the loader and then call the controller method in which you fill your controls with data.