JButton actionPerformed method giving Null

Question

So I have a program I'm writing to allow the user to input text values for attributes of a "Novel" and "Magazine" class that I've designed, however I'm having an issue with my actionListener where it gives me a null pointer exception whenever I trigger the action. My guess is it has something to do with me having the switch statement

switch(theList.getSelectedIndex()){
                case -1: JOptionPane.showMessageDialog(null, "You did not select an object type to create!", "Error!", JOptionPane.ERROR_MESSAGE);
                        break;
                case 0: createObject(theMagazine, titleField, authorField, publisherField, publisherLocationField, copyrightYearField, priceEnterField, ISBNEnterField);
                        JOptionPane.showMessageDialog(null, theMagazine.toString(), "This is The Magazine You Created!", JOptionPane.INFORMATION_MESSAGE);
                        break;
                case 1: createObject(theNovel, titleField, authorField, publisherField, publisherLocationField, copyrightYearField, priceEnterField, ISBNEnterField);
                        theNovel.setHardCover(Boolean.parseBoolean(JOptionPane.showInputDialog(null,"Is this Book a hard cover or not?","Question!",JOptionPane.QUESTION_MESSAGE)));
                        JOptionPane.showMessageDialog(null, theNovel.toString(), "This is The Magazine You Created!", JOptionPane.INFORMATION_MESSAGE);
                        break;
            }

Essentially what I want it to do is be able to call the createObject() method for appropriate attribute values, and then show the JOptionPane's message dialog for the object created using the toString() method contained by both of those classes. I know that the issue is not coming from the method syntax from either of those classes, so I don't necessarily understand where what the issue is is coming from.

This is the source code:

import javax.swing.*;
import javax.swing.border.*;
import java.awt.event.*;
import java.awt.*;
@SuppressWarnings({"serial"})
public class GUI extends JFrame{

static Magazine theMagazine;
static Novel theNovel;

public static void main(String[] args){
    final String[] objectTypes = {"Magazine","Novel"};
    final Border textFieldBorder = BorderFactory.createLineBorder(Color.black, 1);
    final Font theFont = new Font("Times New Roman", 0, 25);
    final JLabel typeSelect = new JLabel("Please select the literature type!");
    final JLabel titleEnter = new JLabel("Enter the title here!");
    final JLabel authorEnter = new JLabel("Enter the Author here!");
    final JLabel publisherEnter = new JLabel("Enter the publisher here!");
    final JLabel pubLocationEnter = new JLabel("Enter the Publishers location here");
    final JLabel enterCopyrightYear = new JLabel("Enter the copyright year here!");
    final JLabel priceEnter = new JLabel("Enter the price here!");
    final JLabel ISBNEnter = new JLabel("Enter the ISBN here!");    

    JList<String> theList = new JList<String>(objectTypes);
    theList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    theList.setLayoutOrientation(JList.HORIZONTAL_WRAP);
    theList.setVisibleRowCount(-1);
    theList.setBorder(textFieldBorder);
    theList.setFont(theFont);

    JTextField titleField = new JTextField();
    titleField.setBorder(textFieldBorder);
    titleField.setFont(theFont);
    titleField.setHorizontalAlignment(JTextField.CENTER);
    JTextField authorField = new JTextField();
    authorField.setBorder(textFieldBorder);
    authorField.setFont(theFont);
    authorField.setHorizontalAlignment(JTextField.CENTER);
    JTextField publisherField = new JTextField();
    publisherField.setBorder(textFieldBorder);
    publisherField.setFont(theFont);
    publisherField.setHorizontalAlignment(JTextField.CENTER);
    JTextField publisherLocationField = new JTextField();
    publisherLocationField.setBorder(textFieldBorder);
    publisherLocationField.setFont(theFont);
    publisherLocationField.setHorizontalAlignment(JTextField.CENTER);
    JTextField copyrightYearField = new JTextField();
    copyrightYearField.setBorder(textFieldBorder);
    copyrightYearField.setFont(theFont);
    copyrightYearField.setHorizontalAlignment(JTextField.CENTER);
    JTextField priceEnterField = new JTextField();
    priceEnterField.setBorder(textFieldBorder);
    priceEnterField.setFont(theFont);
    priceEnterField.setHorizontalAlignment(JTextField.CENTER);
    JTextField ISBNEnterField = new JTextField();
    ISBNEnterField.setBorder(textFieldBorder);
    ISBNEnterField.setFont(theFont);
    ISBNEnterField.setHorizontalAlignment(JTextField.CENTER);

    JButton createObject = new JButton("Create an Object!");
    createObject.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent event){
            switch(theList.getSelectedIndex()){
                case -1: JOptionPane.showMessageDialog(null, "You did not select an object type to create!", "Error!", JOptionPane.ERROR_MESSAGE);
                        break;
                case 0: createObject(theMagazine, titleField, authorField, publisherField, publisherLocationField, copyrightYearField, priceEnterField, ISBNEnterField);
                        JOptionPane.showMessageDialog(null, theMagazine.toString(), "This is The Magazine You Created!", JOptionPane.INFORMATION_MESSAGE);
                        break;
                case 1: createObject(theNovel, titleField, authorField, publisherField, publisherLocationField, copyrightYearField, priceEnterField, ISBNEnterField);
                        theNovel.setHardCover(Boolean.parseBoolean(JOptionPane.showInputDialog(null,"Is this Book a hard cover or not?","Question!",JOptionPane.QUESTION_MESSAGE)));
                        JOptionPane.showMessageDialog(null, theNovel.toString(), "This is The Magazine You Created!", JOptionPane.INFORMATION_MESSAGE);
                        break;
            }
        }
    });
    JButton closeProgram = new JButton("Close the program!");
    closeProgram.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent event){
            System.exit(0);
        }
    });

    JPanel thePanel = new JPanel();
    thePanel.setLayout(new GridLayout(9,2));

    JFrame theFrame;

    //first row
    thePanel.add(typeSelect);
    thePanel.add(theList);

    //second row
    thePanel.add(titleEnter);
    thePanel.add(titleField);

    //third row
    thePanel.add(authorEnter);
    thePanel.add(authorField);

    //fourth row
    thePanel.add(publisherEnter);
    thePanel.add(publisherField);

    //fifth row
    thePanel.add(pubLocationEnter);
    thePanel.add(publisherLocationField);

    //sixth row
    thePanel.add(enterCopyrightYear);
    thePanel.add(copyrightYearField);

    //seventh row
    thePanel.add(priceEnter);
    thePanel.add(priceEnterField);

    //eighth row
    thePanel.add(ISBNEnter);
    thePanel.add(ISBNEnterField);

    //ninth row
    thePanel.add(createObject);
    thePanel.add(closeProgram);

    theFrame = new JFrame();
    theFrame.add(thePanel);
    theFrame.setTitle("Literature Creator!");
    theFrame.setSize(500,500);
    theFrame.setVisible(true);
    theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    theFrame.setResizable(false);   

}
public static void createObject(Literature theLiterature, JTextField titleField, JTextField authorField, JTextField publisherField, JTextField publisherLocationField, 
                        JTextField copyrightYearField, JTextField priceEnterField, JTextField ISBNEnterField){
    theLiterature.setTitle(parseField(titleField));
    theLiterature.setAuthor(parseField(authorField));
    theLiterature.setPublisher(parseField(publisherField));
    theLiterature.setPublisherLocation(parseField(publisherLocationField));
    theLiterature.setCopyrightYear(parseNumField(copyrightYearField));
    theLiterature.setPrice(parseNumField(priceEnterField));
    theLiterature.setISBN(parseNumField(ISBNEnterField));
}
public static String parseField(JTextField field){
    if(field.getText() == null){
        JOptionPane.showMessageDialog(null, "Error! " + field.getName() + " contains no text!", "Error", JOptionPane.ERROR_MESSAGE);
        System.exit(0);
    }
    return field.getText();
}
public static int parseNumField(JTextField field){
    if(field.getText() == null){
        JOptionPane.showMessageDialog(null, "Error! " + field.getName() + " contains no text!", "Error", JOptionPane.ERROR_MESSAGE);
        System.exit(0);
    }
    try{
        Integer.parseInt(field.getText());
    }catch(NumberFormatException nfe){
        JOptionPane.showMessageDialog(null, "Error! Value in field " + field.getName() + " was not a valid number!", "Error!", JOptionPane.ERROR_MESSAGE);
        System.exit(0);
    }
    return Integer.parseInt(field.getText());
}

}

Here is the text from the error message: http://pastebin.com/HRi9jbSD

Any help is greatly appreciated!

@DM hahahahaha it would look like I did that nowhere... Whoops, a silly error I guess, but its been a long long day. Thank you! — Dan Mallory, Feb 21 '17 at 20:10

score 0 · Accepted Answer · answered Feb 21 '17 at 20:11

0

By default Java assigns null to a new defined variable. This static variable

static Magazine theMagazine;

is null when you pass it to the createObject(...) method.

You need to create new Magazine object (or load it somehow) and assign it to the theMagazine variable.

answered Feb 21 '17 at 20:11

Flood2d

1,338
8
9

thank you ! I realize that now. I was aware of that default null value, but it has been a rather long day so after much scanning I still had not seen that could be the issue since my brain wasn't regestering it.. Cheers! – Dan Mallory Feb 22 '17 at 00:16

JButton actionPerformed method giving Null

1 Answers1