Java UI打印空值而不是txt文件中的文本

（已编辑）尝试制作一个购物车，当我点击一本书时，它从文本文件中获取书名，然后获取值并将其添加或删除到总数中

目前，我没有所有的代码，只是从文本文件中提取文本信息。当我当前启动程序时，它会将“Null”值打印到屏幕上，而不是打印书名

原始工作文件

package shoppingcart2;
import java.awt.BorderLayout;
import java.awt.Font;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.*;
import javafx.application.Application;
import static javafx.application.Application.launch;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.control.ListView;
import javafx.scene.control.ComboBox;
import javafx.scene.layout.VBox;
import javafx.scene.layout.HBox;
import javafx.scene.layout.StackPane;
import javafx.scene.layout.GridPane;
import javafx.scene.transform.Scale;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.geometry.Pos;
import javafx.geometry.Insets;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;


public class ShoppingCart2 extends Application
{
    private JPanel listPanel;
    private JPanel shoppingPanel;
    private JPanel buttonsPanel;
    private JList listItems;

    private JButton addButton;
    private JButton removeButton;
    private JButton clearButton;
    private JButton checkoutButton;

    private String[] listArray = new String[7];
    private java.awt.List cartItems = new java.awt.List();

    private final double salesTax = 0.06;

    public static void main(String[] args)
    {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws FileNotFoundException
    {
    //list view items book
    ListView<String> listView = new ListView<>();
    listView.setPrefSize(200, 170);
    listView.getItems().addAll(listArray);
    // create label to display the selection
    Label selectedNameLabel = new Label("Select a Book");
    //Button for selection
    Button getButton = new Button("Add to Cart");
    //Event for Add to cart button
    getButton.setOnAction(event ->
    {
        //Get book
        String selected = listView.getSelectionModel().getSelectedItem();
        //Display selected item in label
        selectedNameLabel.setText(selected);
    });

    String line;
        int index = 0;

        File file = new File("BookPrices.txt");
        Scanner fileReader = new Scanner(file);

        while(fileReader.hasNext())
        {
            line = fileReader.nextLine();
            String [] titles = line.split(",");
            listArray[index] = titles[0];
            index++;    
        }

    //Controls to VBox
    VBox vbox = new VBox(10, listView, selectedNameLabel, getButton);
    vbox.setPadding(new Insets(10));
    vbox.setAlignment(Pos.CENTER);

    //Show
    Scene scene = new Scene(vbox);
    primaryStage.setScene(scene);
    primaryStage.show();

    }
}

---

操作顺序错误

    public static void main(String[] args)
    {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws FileNotFoundException
    {

            String line;
        int index = 0;

        File file = new File("BookPrices.txt");
        Scanner fileReader = new Scanner(file);

        while(fileReader.hasNext())
        {
            line = fileReader.nextLine();
            String [] titles = line.split(",");
            listArray[index] = titles[0];
            index++;    
        }

    //list view items book
    ListView<String> listView = new ListView<>();
    listView.setPrefSize(200, 170);
    listView.getItems().addAll(listArray);
    // create label to display the selection
    Label selectedNameLabel = new Label("Select a Book");
    //Button for selection
    Button getButton = new Button("Add to Cart");
    //Event for Add to cart button
    getButton.setOnAction(event ->
    {
        //Get book
        String selected = listView.getSelectionModel().getSelectedItem();
        //Display selected item in label
        selectedNameLabel.setText(selected);
    });

publicstaticvoidmain（字符串[]args）
{
发射（args）；
}
@凌驾
public void start（Stage primaryStage）引发FileNotFoundException
{
弦线；
int指数=0；
File File=新文件（“BookPrices.txt”）；
Scanner fileReader=新扫描仪（文件）；
while（fileReader.hasNext（））
{
line=fileReader.nextLine（）；
String[]titles=line.split（“，”）；
listArray[index]=标题[0]；
索引++；
}
//列表查看项目手册
ListView ListView=新建ListView（）；
setPrefSize（200170）；
listView.getItems（）.addAll（listArray）；
//创建标签以显示所选内容
标签selectedNameLabel=新标签（“选择一本书”）；
//选择按钮
Button getButton=新按钮（“添加到购物车”）；
//添加到购物车按钮的事件
getButton.setOnAction（事件->
{
//拿到书
所选字符串=listView.getSelectionModel（）.getSelectedItem（）；
//在标签中显示所选项目
selectedNameLabel.setText（已选）；
});

    public static void main(String[] args)
    {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws FileNotFoundException
    {

            String line;
        int index = 0;

        File file = new File("BookPrices.txt");
        Scanner fileReader = new Scanner(file);

        while(fileReader.hasNext())
        {
            line = fileReader.nextLine();
            String [] titles = line.split(",");
            listArray[index] = titles[0];
            index++;    
        }

    //list view items book
    ListView<String> listView = new ListView<>();
    listView.setPrefSize(200, 170);
    listView.getItems().addAll(listArray);
    // create label to display the selection
    Label selectedNameLabel = new Label("Select a Book");
    //Button for selection
    Button getButton = new Button("Add to Cart");
    //Event for Add to cart button
    getButton.setOnAction(event ->
    {
        //Get book
        String selected = listView.getSelectionModel().getSelectedItem();
        //Display selected item in label
        selectedNameLabel.setText(selected);
    });