Head First Java QuizCardBuilder not saving files correctly

[Matthew Busse]

Hello, I'm learning java from the Head First book.

I've been trying to make their QuizCardBuilder and QuizCardPlayer programs, but the QuizCardPlayer is throwing an exception when I try to load a card set:

c:\java>java QuizCardPlayer
make a card
couldn't read the card file

java.lang.ArrayIndexOutOfBoundsException: 0
        at QuizCardPlayer.makeCard(QuizCardPlayer.java:102)
        at QuizCardPlayer.loadFile(QuizCardPlayer.java:88)
        at QuizCardPlayer.access$800(QuizCardPlayer.java:7)
        at QuizCardPlayer$OpenMenuListener.actionPerformed(QuizCardPlayer.java:7
7)
        at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
        at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
        at javax.swing.AbstractButton.doClick(Unknown Source)
        at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
        at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown
Source)
        at java.awt.Component.processMouseEvent(Unknown Source)
        at javax.swing.JComponent.processMouseEvent(Unknown Source)
        at java.awt.Component.processEvent(Unknown Source)
        at java.awt.Container.processEvent(Unknown Source)
        at java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)

I think it has to do with how the other program, the QuizCardBuilder is saving files.

Here's the code for the saveFile method:

private void saveFile(File file) {
		try {
			BufferedWriter writer = new BufferedWriter(new FileWriter(file));
			
			for(QuizCard card:cardList) {
				writer.write(card.getQuestion() + "/");
				writer.write(card.getAnswer() + "\n");
			}
			
			writer.close();

		} catch(IOException ex) {
			System.out.println("couldn't write the cardList out");
			ex.printStackTrace();
		}
	}

If I open up the saved file and just look at it in notepad, the new line doesn't appear to get added after the answer. Instead, I just see another /, similar to what is added after the Question. In fact, if I chance the /n to something else, it still adds a /, so I'm not sure what's going on with that. Does anyone have any idea what's going on here?

Thanks

[Bobby Smallman]

Firstly...Welcome to Java Ranch!

Now that is out of the way, if you could please post at the very least the method which is creating the error itself, looks like it is the makeCard method. It has been awhile since I did the Head First Java examples.

Also, please use the code boxes built into the forums when placing code in your posts, it makes it easier to read and go through which in turn makes your posts easier to reply to.

[Matthew Busse]

Sorry for my lack of etiquette!

I think there are 2 methods related to loading the cards, I'll also include the code for the showNextCard:

   
public class OpenMenuListener implements ActionListener {
		public void actionPerformed(ActionEvent ev) {
			JFileChooser fileOpen = new JFileChooser();
			fileOpen.showOpenDialog(frame);
			loadFile(fileOpen.getSelectedFile());
		}
	}

	private void loadFile (File file) {
		
		cardList = new ArrayList<QuizCard>();
		try {
			BufferedReader reader = new BufferedReader(new FileReader(file));
			String line = null;
			while ((line = reader.readLine()) != null) {
				makeCard(line);
			}
			reader.close();

		} catch(Exception ex) {
			System.out.println("couldn't read the card file");
			ex.printStackTrace();
		}

		showNextCard();
	}

	private void makeCard(String lineToParse) {
		String[] result = lineToParse.split("/");
		QuizCard card = new QuizCard(result[0], result[1]);
		cardList.add(card);
		System.out.println("made a card");
	}

	private void showNextCard() {
		currentCard = cardList.get(currentCardIndex);
		currentCardIndex++;
		display.setText(currentCard.getQuestion());
		nextButton.setText("Show Answer");
		isShowAnswer = true;
	}
 

Thanks a lot for your help, I really appreciate it!

[Campbell Ritchie]

I have added code tags to your first post; you can see how much better it looks. Which is line 102?

[Joanne Neal]

Campbell Ritchie wrote:I have added code tags to your first post; you can see how much better it looks. Which is line 102?

I'd bet it was line 31 in his second post and that lineToParse.split("/") is returning an empty array. i think that is only possible if lineToParse is an empty String. Does your input file contain any blank lines ?

Edit: Just tried it and split on an empty String returns an array of length 1. I can't see anything else in the makeCard method that would throw an ArrayIndexOutOfBoundsException exception so there must be something that causes split to return an empty array. Can you put a System.out.println() call before line 31 that shows the value of lineToParse.

Edit 2: split will return an empty array if lineToParse contains just / characters. Do you have such a line in your input file ?

[Campbell Ritchie]

But if you have a 1-element array, and try to get [1] on it . . . (Also line 31)

[Matthew Busse]

Here is the text from the saved file:

what is best?/blah blah blah
/
what is super?/yada yada yada
/
/


Hmm, in notepad, it doesn't appear to have a new line, but when I copy it into here, it looks like the new line is there.

In the example in the book, it's not supposed to add the / after every line.

Ok, here's all the code for QuizCardBuilder:

import java.util.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
import java.io.*;

public class QuizCardPlayer {
    private JTextArea display;
    private JTextArea answer;
    private ArrayList<QuizCard> cardList;
    private QuizCard currentCard;
    private int currentCardIndex;
    private JFrame frame;
    private JButton nextButton;
    private boolean isShowAnswer;

    public static void main (String[] args) {
        QuizCardPlayer reader = new QuizCardPlayer();
        reader.go();
    }

    public void go() {
        frame = new JFrame("Quiz Card Player");
        JPanel mainPanel = new JPanel();
        Font bigFont = new Font("sanserif", Font.BOLD, 24);
        
        display = new JTextArea(10,20);
        display.setFont(bigFont);

        display.setLineWrap(true);
        display.setEditable(false);

        JScrollPane qScroller = new JScrollPane(display);
        qScroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        qScroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        
        nextButton = new JButton("Show Question");
        nextButton.addActionListener(new NextCardListener());
        
        mainPanel.add(qScroller);
        mainPanel.add(nextButton);

        JMenuBar menuBar = new JMenuBar ();
        JMenu fileMenu = new JMenu("File");
        JMenuItem loadMenuItem = new JMenuItem("Load card set");
        loadMenuItem.addActionListener(new OpenMenuListener());
        fileMenu.add(loadMenuItem);
        menuBar.add(fileMenu);
        frame.setJMenuBar(menuBar);
        frame.getContentPane().add(BorderLayout.CENTER, mainPanel);
        frame.setSize(640,500);
        frame.setVisible(true);
    }

    public class NextCardListener implements ActionListener {
        public void actionPerformed(ActionEvent ev) {
            if (isShowAnswer) {
                display.setText(currentCard.getAnswer());
                nextButton.setText("Next Card");
                isShowAnswer = false;
            } else {
                if (currentCardIndex < cardList.size()) {
                    showNextCard();

                } else {
                    display.setText("That was the last card");
                    nextButton.setEnabled(false);
                }
            }
        }
    }

    public class OpenMenuListener implements ActionListener {
        public void actionPerformed(ActionEvent ev) {
            JFileChooser fileOpen = new JFileChooser();
            fileOpen.showOpenDialog(frame);
            loadFile(fileOpen.getSelectedFile());
        }
    }

    private void loadFile (File file) {
        
        cardList = new ArrayList<QuizCard>();
        try {
            BufferedReader reader = new BufferedReader(new FileReader(file));
            String line = null;
            while ((line = reader.readLine()) != null) {
                makeCard(line);
            }
            reader.close();

        } catch(Exception ex) {
            System.out.println("couldn't read the card file");
            ex.printStackTrace();
        }

        showNextCard();
    }

    private void makeCard(String lineToParse) {
        String[] result = lineToParse.split("/");
        System.out.println(result[0] + result[1]);
        QuizCard card = new QuizCard(result[0], result[1]);
        cardList.add(card);
        System.out.println("made a card");
    }

    private void showNextCard() {
        currentCard = cardList.get(currentCardIndex);
        currentCardIndex++;
        display.setText(currentCard.getQuestion());
        nextButton.setText("Show Answer");
        isShowAnswer = true;
    }
}    

I added the println to print out the string array result. When I try to load a card, this is what I get:

c:\java>java QuizCardPlayer
what is best?blah blah blah
made a card
couldn't read the card file
java.lang.ArrayIndexOutOfBoundsException: 0
        at QuizCardPlayer.makeCard(QuizCardPlayer.java:102)
        at QuizCardPlayer.loadFile(QuizCardPlayer.java:88)
        at QuizCardPlayer.access$800(QuizCardPlayer.java:7)
        at QuizCardPlayer$OpenMenuListener.actionPerformed(QuizCardPlayer.java:7
7)
        at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
        at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
        at javax.swing.AbstractButton.doClick(Unknown Source)
        at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
        at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown
Source)
        at java.awt.Component.processMouseEvent(Unknown Source)
        at javax.swing.JComponent.processMouseEvent(Unknown Source)
        at java.awt.Component.processEvent(Unknown Source)
        at java.awt.Container.processEvent(Unknown Source)
        at java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)

It looks like it's loading the first card correctly, but then not the second one, right?

Thanks again for your help!

[Sudipta Laha]

HI,
Give a SOP in line 88 before calling the method. You will get to know whats coming in the line and track the issue.
If / is the issue . you can modify your file or put some validation in your method

[Matthew Busse]

Hello,

When I add an SOP before line 88, this is what I get:

c:\java>java QuizCardPlayer
text in line is:what is best?/blah blah blah
text in result string array is:what is best?blah blah blah
made a card
text in line is:/
couldn't read the card file
java.lang.ArrayIndexOutOfBoundsException: 0
        at QuizCardPlayer.makeCard(QuizCardPlayer.java:103)
        at QuizCardPlayer.loadFile(QuizCardPlayer.java:89)
        at QuizCardPlayer.access$800(QuizCardPlayer.java:7)
        at QuizCardPlayer$OpenMenuListener.actionPerformed(QuizCardPlayer.java:7
7)
        at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
        at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
        at javax.swing.AbstractButton.doClick(Unknown Source)
        at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
        at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown
Source)
        at java.awt.Component.processMouseEvent(Unknown Source)
        at javax.swing.JComponent.processMouseEvent(Unknown Source)
        at java.awt.Component.processEvent(Unknown Source)
        at java.awt.Container.processEvent(Unknown Source)
        at java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)   

It's reading the first line ok, but when it tries to read the second line, it gets to the / and that messes up the split line. So I still don't understand why the QuizCardBuilder program is adding / after every line when it creates the saved file.

Here's the code for that method again:

private void saveFile(File file) {
        try {
            BufferedWriter writer = new BufferedWriter(new FileWriter(file));
            
            for(QuizCard card:cardList) {
                writer.write(card.getQuestion() + "/");
                writer.write(card.getAnswer() + "\n");
            }
            
            writer.close();

        } catch(IOException ex) {
            System.out.println("couldn't write the cardList out");
            ex.printStackTrace();
        }
    }    

After it writes the text from getAnswer, it should just add an new line, not a /, right?

Many many thanks for all your help.

[Campbell Ritchie]

Does that mean you are writing the results into a file before you read them? Joanne and I have (I think) already given the explanation for the out of bounds Exception. But you need to work out why you are getting such a short line.

Which page is this exercise on?

[Matthew Busse]

The QuizCardBuilder exercise is on p.450, and the QuizCardPlayer exercise is on p.456.

The goal of the exercises is to learn how to write to text files and read from text files.

[Matthew Busse]

I think I'm getting a short line because the QuizCardBuilder is writing to the file incorrectly, adding a / after the \n. Does the write method from the JAVA API automatically add a / when it writes a line or something like that?

[Campbell Ritchie]

You will have to check the API for the write method, but as far as I remember, no it doesn't add a /. You would appear to be getting one more / than you need.
Put this block immediately after your last "write" instruction. Beware: I have found some spelling errors in it; there might be some I haven't noticed.

try
{
    Thread.sleep(30000);
}
catch (InterruptedException ie)
{
    ie.printStackTrace();
}

That will give you a 30-second delay, during which you can try and open the destination file with a text editor and check the last line for whether it is question/answer or only /.

[Joanne Neal]

Campbell Ritchie wrote:But if you have a 1-element array, and try to get [1] on it . . . (Also line 31)

True, but the exception tells you which element is out of bounds.

Matthew Busse wrote:

java.lang.ArrayIndexOutOfBoundsException: 0

[Campbell Ritchie]

Yes, I missed that bit. Sorry.

[Campbell Ritchie]

Dugie notvalid,
Your post was moved to a new topic.