How to Populate GUI Fields from JList

[no1zson]

I am a beginner here, still in my first Java class, so I hope this question is not so simple as to offend anyone, but I am finishing up my cd inventory program.
Adding some GUI buttons to manipulate data in my JList.
JList is beyond the scope of my class so I am finding help hard to come by.
I only have two weeks of class left, so it is too late to go back to my array now.
It is sink or swim with what I have. :o)

For my question ... I have an ADD button that works like a charm, populates JList from my fields. I am now working on the PREV button to pull the information back to the fields from the previous cd. I have coded and coded but I am obviously doing something wrong because it keeps erroring upon execution.
Compiles fine, but will not run. Keep getting:
Exception in thread "AWT-EventQueue-0" java.lang.Numbe rFormatExceptio n: For input string: ""
at java.lang.Numbe rFormatExceptio n.forInputStrin g(NumberFormatE xception.java:4 8)
at java.lang.Integ er.parseInt(Int eger.java:468)
at java.lang.Integ er.parseInt(Int eger.java:497)
at Inventory2.btnA ddActionPerform ed(Inventory2.j ava:255)
at Inventory2.acce ss$000(Inventor y2.java:10)
at Inventory2$2.ac tionPerformed(I nventory2.java: 155)
at javax.swing.Abs tractButton.fir eActionPerforme d(AbstractButto n.java:1849)
at javax.swing.Abs tractButton$Han dler.actionPerf ormed(AbstractB utton.java:2169 )
at javax.swing.Def aultButtonModel .fireActionPerf ormed(DefaultBu ttonModel.java: 420)
at javax.swing.Def aultButtonModel .setPressed(Def aultButtonModel .java:258)
at javax.swing.pla f.basic.BasicBu ttonListener.mo useReleased(Bas icButtonListene r.java:236)
at java.awt.Compon ent.processMous eEvent(Componen t.java:5517)
at javax.swing.JCo mponent.process MouseEvent(JCom ponent.java:313 5)
at java.awt.Compon ent.processEven t(Component.jav a:5282)
at java.awt.Contai ner.processEven t(Container.jav a:1966)
at java.awt.Compon ent.dispatchEve ntImpl(Componen t.java:3984)
at java.awt.Contai ner.dispatchEve ntImpl(Containe r.java:2024)
at java.awt.Compon ent.dispatchEve nt(Component.ja va:3819)
at java.awt.Lightw eightDispatcher .retargetMouseE vent(Container. java:4212)
at java.awt.Lightw eightDispatcher .processMouseEv ent(Container.j ava:3892)
at java.awt.Lightw eightDispatcher .dispatchEvent( Container.java: 3822)
at java.awt.Contai ner.dispatchEve ntImpl(Containe r.java:2010)
at java.awt.Window .dispatchEventI mpl(Window.java :1791)
at java.awt.Compon ent.dispatchEve nt(Component.ja va:3819)
at java.awt.EventQ ueue.dispatchEv ent(EventQueue. java:463)
at java.awt.EventD ispatchThread.p umpOneEventForH ierarchy(EventD ispatchThread.j ava:242)
at java.awt.EventD ispatchThread.p umpEventsForHie rarchy(EventDis patchThread.jav a:163)
at java.awt.EventD ispatchThread.p umpEvents(Event DispatchThread. java:157)
at java.awt.EventD ispatchThread.p umpEvents(Event DispatchThread. java:149)
at java.awt.EventD ispatchThread.r un(EventDispatc hThread.java:11 0)

Here is my code. Everything works except the Previous Button action event.
Any suggestions?

import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.text.*;
import java.lang.*;
 
public class Inventory2 extends JFrame
{
    private JLabel cdNameLabel; // name label 
    private JLabel artistLabel; // item number label 
    private JLabel nstockLabel; // units in stock label 
    private JLabel priceLabel; // price each label 
    private JLabel itemLabel; // item number label 
    private JTextField cdNameField; // name display 
    private JTextField artistField; // artist display 
    private JFormattedTextField nstockField; // units in stock display 
    private JFormattedTextField priceField; // price each display 
    private JTextField itemField; // item number display 
    private NumberFormat nstockFormat; // format field and parse numbers 
    private NumberFormat priceFormat; // format field and parse numbers 
    private JButton btnAdd; // first button 
    private JButton btnPrev; // previous button 
    private JButton btnNext; // next button 
    private JButton btnDel; // last button 
    private JButton btnFirst; // first button
    private JButton btnLast; // last button
    private JButton btnModify; // modify button
    private JButton btnSave; // save button
    private JButton btnSearch; // search button
    private JPanel buttonJPanel; // JPanle to hold buttons 
    private JPanel fieldJPanel; // JPanel to hold labels and displays 
    private JPanel fontJPanel; // JPanel to display logo 
    private int currCD; 
    private double total = 0; // variable for total inventory 
    private JList Inventorylist; // JList to take place of old array
    private DefaultListModel listModel;
    private JScrollPane jScrollPanel;  
    private float Invtotal = .00f;
 
    public Inventory2() // create class and method to perform GUI build 
    { 
        initComponents(); 
    } 
 
    private void initComponents() 
    { 
        // create label names 
        cdNameLabel = new JLabel("CD Name:"); 
        artistLabel = new JLabel("Artist:");
        nstockLabel = new JLabel("In Stock:"); 
        priceLabel = new JLabel("Each Item Cost:$"); 
        itemLabel = new JLabel("Item Number:"); 
 
 
        // initial fields
        cdNameField = new JTextField(25);
        cdNameField.setEditable(true);
        artistField = new JTextField(15);
        artistField.setEditable(true);
        nstockField = new JFormattedTextField(nstockFormat);
        nstockField.setEditable(true);
        nstockField.setColumns(5);
        priceField = new JFormattedTextField(priceFormat);
        priceField.setEditable(true);
        priceField.setColumns(5);
        itemField = new JTextField(4);
        itemField.setEditable(true);
 
        // JList
        jScrollPanel = new JScrollPane();
        Inventorylist = new JList(); 
        currCD = 0;
 
 
        // buttons 
        btnAdd = new JButton(); 
        btnNext = new JButton(); 
        btnPrev = new JButton(); 
        btnDel = new JButton();
        btnLast = new JButton();
        btnFirst = new JButton();
        btnModify = new JButton(); 
        btnSave = new JButton();
        btnSearch = new JButton();
 
        getContentPane().setLayout(new FlowLayout());
 
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
 
 
        // place textFields and labels
 
        //artist
        artistLabel.setText("Artist"); 
        getContentPane().add(artistLabel); 
 
        artistField.setMinimumSize(new Dimension(70,20)); 
        artistField.setPreferredSize(new Dimension(70,20));
        getContentPane().add(artistField); 
 
        // cd name
        cdNameLabel.setText("CD Name"); 
        getContentPane().add(cdNameLabel); 
 
        cdNameField.setMinimumSize(new Dimension(70,20)); 
        cdNameField.setPreferredSize(new Dimension(70,20));
        getContentPane().add(cdNameField);
 
        // copies in stock
        nstockLabel.setText("Copies In Stock"); 
        getContentPane().add(nstockLabel); 
 
        nstockField.setMinimumSize(new Dimension(5,20)); 
        nstockField.setPreferredSize(new Dimension(5,20));
        getContentPane().add(nstockField); 
 
        //price of cd
        priceLabel.setText("Price"); 
        getContentPane().add(priceLabel); 
 
        priceField.setMinimumSize(new Dimension(20,20)); 
        priceField.setPreferredSize(new Dimension(20,20));
        getContentPane().add(priceField); 
 
        //item number of cd
        itemLabel.setText("Item Number"); 
        getContentPane().add(itemLabel); 
 
        itemField.setMinimumSize(new Dimension(5,20)); 
        itemField.setPreferredSize(new Dimension(5,20));
        getContentPane().add(itemField); 
 
 
        // add listeners
 
        btnAdd.setText("Add");
        btnAdd.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnAdd);
 
        // PREVIOUS
        btnPrev.setText("Previous");
        btnPrev.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnPrev);
 
        // NEXT
        btnNext.setText("Next");        btnNext.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnNext);
 
        // SEARCH
        btnSearch.setText("Search");
        btnSearch.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnSearch);
 
        // FIRST
        btnFirst.setText("First");
        btnFirst.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnFirst);
 
        // LAST
        btnLast.setText("Last");
        btnLast.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnLast);
 
        // MODIFY
        btnModify.setText("Modify");
        btnModify.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnModify);
 
        // SAVE
        btnSave.setText("Save");
        btnSave.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnSave);
 
        // DELETE
        btnDel.setText("Delete");
        btnDel.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnAddActionPerformed(evt);
            }
        });
        getContentPane().add(btnDel);
 
 
        // new Jlist model
        listModel = new DefaultListModel();
        Inventorylist.setModel(listModel);
 
        jScrollPanel.setViewportView(Inventorylist);
 
        getContentPane().add(jScrollPanel);
 
        pack();
    }// close
 
 
        private void btnAddActionPerformed(ActionEvent evt)
        {
            // Create cd to add
            CdwArtist newCD = new CdwArtist();
            newCD.setArtist(artistField.getText());
            newCD.setName(cdNameField.getText());    
            newCD.setItemno(Integer.parseInt(itemField.getText()));
            newCD.setNstock(Integer.parseInt(nstockField.getText()));
            newCD.setPrice(Float.parseFloat(priceField.getText()));
 
            // Add cd to list
            listModel.addElement(newCD);
            currCD = listModel.size()-1;  // sets currCD to added index
 
 
            // Clear the text fields after add
            artistField.setText(null);
            cdNameField.setText(null);    
            itemField.setText(null);
            nstockField.setText(null);
         priceField.setText(null);
 
            }// end ADD
 
        private void btnPrevActionPerformed(ActionEvent evt)
        {
            // Grab Previous cd 
            CdwArtist newCD = (CdwArtist) listModel.get( currCD-- );
            newCD.setArtist(artistField.getText());
            newCD.setName(cdNameField.getText());    
            newCD.setItemno(Integer.parseInt(itemField.getText()));
            newCD.setNstock(Integer.parseInt(nstockField.getText()));
            newCD.setPrice(Float.parseFloat(priceField.getText()));        
 
            }// end PREV
 
        // run it
        public static void main(String args[])
        {
        java.awt.EventQueue.invokeLater(new Runnable()
            {
            public void run()
                {
                new Inventory2().setVisible(true);
               }
            });
        }
 
} // close class

[JosAH]

According to that stacktrace the problem occurs in one of these lines:

newCD.setItemno(Integer.parseInt(itemField.getText()));
newCD.setNstock(Integer.parseInt(nstockField.getText()));
 

This indicates that either the itemField or the nstockFied don't contain a valid
integer number. As far as I can see those fields are JTextFields so you should
either supply valid text for those fileds or re-implement this part of your software.

kind regards,

Jos

[blazedaces]

java.lang.Numbe rFormatExceptio n.forInputStrin g(NumberFormatE xception.java:4 8)
at java.lang.Integ er.parseInt(Int eger.java:468)
at java.lang.Integ er.parseInt(Int eger.java:497)
at Inventory2.btnA ddActionPerform ed(Inventory2.j ava:255)

Ok, so let's look at the printed error, the problem. If we know what the problem is and where it is we will better know how to solve it.

Now, why does java throw a NumberFormatExc eption? Let's look at the documentation (if I were you, I would make this a habit):

Thrown to indicate that the application has attempted to convert a string to one of the numeric types, but that the string does not have the appropriate format.

Now we know what the problem is, next we'll try and understand where it is. The first place the error is caught inside of your class (as opposed to class Integer) is here: at Inventory2.btnA ddActionPerform ed(Inventory2.j ava:255). So here is that class:

        private void btnAddActionPerformed(ActionEvent evt)
        {
            // Create cd to add
            CdwArtist newCD = new CdwArtist();
            newCD.setArtist(artistField.getText());
            newCD.setName(cdNameField.getText());    
            newCD.setItemno(Integer.parseInt(itemField.getText()));
            newCD.setNstock(Integer.parseInt(nstockField.getText())); //This is where it says the error shows up.
            newCD.setPrice(Float.parseFloat(priceField.getText()));
 
            // Add cd to list
            listModel.addElement(newCD);
            currCD = listModel.size()-1;  // sets currCD to added index
 
 
            // Clear the text fields after add
            artistField.setText(null);
            cdNameField.setText(null);    
            itemField.setText(null);
            nstockField.setText(null);
         priceField.setText(null);
 
            }// end ADD
 

Quickly, let's take a look at the documentation to know why does Integer.parseIn t(String s) throw that error and it says is throws it because:
"NumberFormatEx ception - if the string does not contain a parsable integer."

I don't know exactly the problem yet, but I'm pretty sure by doing the following you can get to the bottom of it: add System.out.prin t for the strings in the method that undergo parseInt. Change your method to look like this and tell us what you see as the output:

        private void btnAddActionPerformed(ActionEvent evt)
        {
            // Create cd to add
            CdwArtist newCD = new CdwArtist();
            newCD.setArtist(artistField.getText());
            newCD.setName(cdNameField.getText());    
            newCD.setItemno(Integer.parseInt(itemField.getText()));
                        System.out.println("itemField.getText(): " + itemField.getText());
            newCD.setNstock(Integer.parseInt(nstockField.getText())); //This is where it says the error shows up.
                        System.out.println("nstockField.getText(): " + nstockField.getText());
            newCD.setPrice(Float.parseFloat(priceField.getText()));
 
            // Add cd to list
            listModel.addElement(newCD);
            currCD = listModel.size()-1;  // sets currCD to added index
 
 
            // Clear the text fields after add
            artistField.setText(null);
            cdNameField.setText(null);    
            itemField.setText(null);
            nstockField.setText(null);
         priceField.setText(null);
 
            }// end ADD
 

Hope that works and good luck,

-blazed

[no1zson]

I do not know how to reply to this. You both seem to indicate that the problem lies in my ADD button action event, but that works fine.

It is not until I coded my PREV button action event that the problem occurs.

Both my nstock and itemno fields are in fact intergers, and my application works without flaw until I coded this PREV button. Does that not indicate a probelm with the PREV button code?

    private void btnPrevActionPerformed(ActionEvent evt)
        {
            // Grab Previous cd 
            CdwArtist newCD = (CdwArtist) listModel.get( currCD-- );
            newCD.setArtist(artistField.getText());
            newCD.setName(cdNameField.getText());    
            newCD.setItemno(Integer.parseInt(itemField.getText()));
            newCD.setNstock(Integer.parseInt(nstockField.getText()));
            newCD.setPrice(Float.parseFloat(priceField.getText()));        
 
            }// end PREV

All this button should do is take the information from the previous cd and put it back into my text fields for viewing.

It works fine when I enter the information into the fields, hit ADD and enter it into my JList.

[JosAH]

I do not know how to reply to this. You both seem to indicate that the problem lies in my ADD button action event, but that works fine.

It is not until I coded my PREV button action event that the problem occurs.

Both my nstock and itemno fields are in fact intergers, and my application works without flaw until I coded this PREV button. Does that not indicate a probelm with the PREV button code?

    private void btnPrevActionPerformed(ActionEvent evt)
        {
            // Grab Previous cd 
            CdwArtist newCD = (CdwArtist) listModel.get( currCD-- );
            newCD.setArtist(artistField.getText());
            newCD.setName(cdNameField.getText());    
            newCD.setItemno(Integer.parseInt(itemField.getText()));
            newCD.setNstock(Integer.parseInt(nstockField.getText()));
            newCD.setPrice(Float.parseFloat(priceField.getText()));        
 
            }// end PREV

All this button should do is take the information from the previous cd and put it back into my text fields for viewing.

It works fine when I enter the information into the fields, hit ADD and enter it into my JList.

You also use that same 'add' method in line 154 or so; as a matter of fact you
use that method for every action when whatever button is pressed. I'm afraid it's
a copy/paste thingy ;-)

kind regards,

Jos

[no1zson]

You are right, I am a beginner but that is just dumb on my part.
Copy/paste is exactly what I did and did not catch the error until you pointed it out. I wanted to work through one button at a time, so did not change the names when I did it because the new ones were not coded yet and it would error out.

I have however now changed the PREV button, and although the errors have moved down the chain a bit (I am at least in the right button now) they still point to errors with the same lines of code.

// PREVIOUS
        btnPrev.setText("Previous");
        btnPrev.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnPrevActionPerformed(evt);
            }
        });
        getContentPane().add(btnPrev);

Would the method types be different pulling information from the JList than they were going in? If it were an INT going in, it would be an INT coming back out would it not? The field is coded as such, so I would think nothing would change there. I thought I just had a syntax issue, but it is looking like a bigger problem ... no?

[JosAH]

You are right, I am a beginner but that is just dumb on my part.
Copy/paste is exactly what I did and did not catch the error until you pointed it out. I wanted to work through one button at a time, so did not change the names when I did it because the new ones were not coded yet and it would error out.

I have however now changed the PREV button, and although the errors have moved down the chain a bit (I am at least in the right button now) they still point to errors with the same lines of code.

// PREVIOUS
        btnPrev.setText("Previous");
        btnPrev.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent evt)
            {
                btnPrevActionPerformed(evt);
            }
        });
        getContentPane().add(btnPrev);

Would the method types be different pulling information from the JList than they were going in? If it were an INT going in, it would be an INT coming back out would it not? The field is coded as such, so I would think nothing would change there. I thought I just had a syntax issue, but it is looking like a bigger problem ... no?

Well, as far as I can see your btnPrevActionPe rformed method suffers from that
same copy/paste virus too: i.e. it too tries to parse an Integer from a JTextField.

I think you should design your prev/next/add/whatever actions first before you
attempt to implement anything at all.

kind regards,

Jos

[no1zson]

That is the crux of my problem, this is my design, this is what I sat down and came up with.
I have never done this before, so each step I take is the first in that direction, I do not know any other way to do this.
I understand what you are saying, (I think)

newCD.setItemno(Integer.parseInt(itemField.getText()));
            newCD.setNstock(Integer.parseInt(nstockField.getText()));
            newCD.setPrice(Float.parseFloat(priceField.getText()));

are all parsing integers, but getting text ....if this is the problem, (which I do not doubt what you say), but why would this work in my ADD button but not here?

[JosAH]

That is the crux of my problem, this is my design, this is what I sat down and came up with.
I have never done this before, so each step I take is the first in that direction, I do not know any other way to do this.
I understand what you are saying, (I think)

newCD.setItemno(Integer.parseInt(itemField.getText()));
            newCD.setNstock(Integer.parseInt(nstockField.getText()));
            newCD.setPrice(Float.parseFloat(priceField.getText()));

are all parsing integers, but getting text ....if this is the problem, (which I do not doubt what you say), but why would this work in my ADD button but not here?

Shouldn't that 'prev' button read 'delete'? From what I see from your code you
want to delete that CD from your inventory. Deleting a CD is easy: just remove
it from your JList model and revalidate the display of it.

kind regards,

Jos

[no1zson]

No. The PREV button should pull in the previous record.
If you see a flaw in my code that does not indicate this please point it out because I do not.

The DELETE button will delete a record, but I have not even started on that buttun yet.
I put the architecture in the code so that I could see it as a reminder of everything I want to accomplish this week. It is one of several buttons I want to code before Friday.
Add was first, it works.
Prev is next, it does not work.
Next, Delete, Search, Modify, First and Last are all to come ....