JavaFX observableArrayList is always overwritten

Question

I'm new on Java and have a little problem.

There are two classes and I have tried to write into a ArrayList in the ChoiceCarController class from the PopupCarEntryController class. With the addCarToList method.

But every time I start this method, the ArrayList is empty or got overwritten.

ChoiceCarController:

import Car;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.Separator;

public class FXMLChoiceCarController implements Initializable {

    private FahrtenbuchFX application;

    public FXMLChoiceCarController() {
        this.carChoiceBox = new ChoiceBox(carChoiceBoxData);
    }

    @FXML
    private void handleSelectButtonAction(ActionEvent event) {
        if (!carChoiceBox.getSelectionModel().isEmpty()) {
            application.FahrtenbuchView();
        } else {

        }
    }

    @FXML
    private void handleAddButtonAction(ActionEvent event) {
        application.showPopup();
    }

    @FXML
    private void handleExitButtonAction(ActionEvent event) {
        System.exit(0);
    }


    public ObservableList<Car> carChoiceBoxData = FXCollections.observableArrayList();

    @FXML
    private ChoiceBox carChoiceBox;

    @FXML
    private void handleCarChoiceBoxAction(ActionEvent event) {

    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        carChoiceBox.getSelectionModel().selectFirst();
        carChoiceBox.setItems(carChoiceBoxData);
//        this.carChoiceBoxData.add(new Car("asdf", "asdf"));
        System.out.println(getCarList());
    }

    public void addCarToList(Car car) {
        System.out.println(getCarList());
        carChoiceBoxData.add(car);
        System.out.println(getCarList());
    }

    public String getCarList() {
        return carChoiceBoxData.toString();
    }

    public void setApp(FahrtenbuchFX application) {
        this.application = application;
    }

}

And the PopupCarEntryController

import Car;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.ComboBox;
import javafx.scene.control.Label;
import javafx.scene.control.Separator;
import javafx.scene.control.TextField;


public class FXMLPopupCarEntryController implements Initializable {

    private FahrtenbuchFX application;

    @FXML
    private Label labelErrorMessage;

    @FXML
    private TextField textFieldProducer;

    @FXML
    private TextField textFieldModel;

    @FXML
    private TextField textFieldEngine;

    @FXML
    private TextField textFieldFuel;

    @FXML
    private TextField textFieldFlag;

    @FXML
    private void handleSaveButtonAction(ActionEvent event) {
        FXMLChoiceCarController carController = new FXMLChoiceCarController();
        carController.addCarToList(new Car(textFieldProducer.getText(), textFieldModel.getText()));

    }

    @FXML
    private void handleCloseButtonAction(ActionEvent event) {
        application.hidePopup();
    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        //TODO
    }

    public void setApp(FahrtenbuchFX application) {
        this.application = application;
    }
}

The thing that I not understood is that, when I initialize the List in the void initialize method and do an out.println in the addCarToList method the result is different. Like when the variable points to an different ArrayList.

Answer 1

That's because every time you are instantiating controller class like this:

FXMLChoiceCarController carController = new FXMLChoiceCarController();

So you are creating list every time like:

public ObservableList<Car> carChoiceBoxData = FXCollections.observableArrayList();

if you want to reuse the list, make your list static like:

public static ObservableList<Car> carChoiceBoxData = FXCollections.observableArrayList();

So you just have one instance of your list.