GUI array information cycler help please

Question

I currently have a program that has 3 classes. Basically one class is the main and has some information hard coded that it submits to one of the other classes. The second class takes that information, formats it and sends it to the third class. The third class creates an array, takes the information from the second class and has a display method that the main can call to display the information.
The program basically spews out all the information in the array in a specific format. The array elements contain strings, ints and doubles. The third class also calculates some things that are displayed with the display method in main.
What I need to do is create a third class. This class needs to make a GUI to display the information. I currently have the programs display method display the information in a GUI but I need it to display each element one at a time with a NEXT and PREVIOUS button. The next button needs to go to the next array element and the previous button obviously needs to go back to the array element.
Here is the code.
//  Inventory Program
//  Created June 20, 2007
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Inventory4 {
    public static void main(String[] args) {
        CD cd;
        Inventory inventory = new Inventory();
        cd = new CDWithGenre(16, "Disney Hits", 11, 13.01f, "Soundtrack");
        inventory.add(cd);
        cd = new CDWithGenre(12, "The Clash", 10, 19.99f, "Classic Rock");
        inventory.add(cd);
        cd = new CDWithGenre(45, "Dixie Chiks", 18, 10.87f, "Country");
        inventory.add(cd);
        cd = new CDWithGenre(32, "The Cure", 62, 25.76f, "Alternative");
        inventory.add(cd);
        cd = new CDWithGenre(18, "MS Office", 27, 99.27f, "None");
        inventory.add(cd);
        inventory.display();    
    } //End main method
} //End Inventory4 class
     /* Defines data from main as CD data and formats it. Calculates value of a title multiplied by its stock.
      Creates compareTo method to be used by Arrays.sort when sorting in alphabetical order. */
class CD implements Comparable{
    //Declares the variables as protected so only this class and subclasses can act on them
    protected int cdSku;        
    protected String cdName;               
    protected int cdCopies;
    protected double cdPrice;
    protected String genre;
    //Constructor
    CD(int cdSku, String cdName, int cdCopies, double cdPrice, String genre) {
        this.cdSku    = cdSku;
        this.cdName   = cdName;
        this.cdCopies = cdCopies;
        this.cdPrice  = cdPrice;
        this.genre = genre;
    // This method tells the sort method what is to be sorted     
    public int compareTo(Object o)
        return cdName.compareTo(((CD) o).getName());
    // Calculates the total value of the copies of a CD
    public double totalValue() {
        return cdCopies * cdPrice;
    // Tells the caller the title
    public String getName() {
        return cdName;       
    //Displays the information stored by the constructor
    public String toString() {
        return String.format("SKU=%2d   Name=%-20s   Stock=%3d   Price=$%6.2f   Value=$%,8.2f",
                              cdSku, cdName, cdCopies, cdPrice, totalValue());
} // end CD class    
     //Class used to add items to the inventory, display output for the inventory and sort the inventory
class Inventory {
    private CD[] cds;
    private int nCount;
     // Creates array cds[] with 10 element spaces
    Inventory() {
        cds = new CD[10];
        nCount = 0;
     // Used by main to input a CD object into the array cds[]
    public void add(CD cd) {
        cds[nCount] = cd;
        ++nCount;
        sort();               
     //Displays the arrays contents element by element into a GUI pane
       public void display() {
        JTextArea textArea = new JTextArea();
        textArea.append("\nThere are " + nCount + " CD titles in the collection\n\n");
        for (int i = 0; i < nCount; i++)
            textArea.append(cds[i]+"\n");
        textArea.append("\nTotal value of the inventory is "+new java.text.DecimalFormat("$0.00").format(totalValue())+"\n\n");
        JFrame invFrame = new JFrame();
        invFrame.getContentPane().add(new JScrollPane(textArea));
        invFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        invFrame.pack();
        invFrame.setLocationRelativeTo(null);
        invFrame.setVisible(true);
     // Steps through the array adding the totalValue for each CD to "total"
    public double totalValue() {
        double total = 0;
        double restock = 0;
        for (int i = 0; i < nCount; i++)
            total += cds.totalValue();                
return total;
     //Method used to sort the array by the the name of the CD
private void sort() {
     Arrays.sort(cds, 0, nCount);
} // end Inventory class
// Subclass of CD. Creates new output string to be used, adds a restocking fee calculation and genre catagory to be displayed.
class CDWithGenre extends CD {
     String genre;
     CDWithGenre(int cdSku, String cdName, int cdCopies, double cdPrice, String genre) {
super(cdSku, cdName, cdCopies, cdPrice, genre);
this.cdName = cdName;
          this.cdCopies = cdCopies;
this.cdPrice = cdPrice;
this.genre = genre;
// Calculates restocking fee based on previous data.
public double restockFee() {
     double total = 0;
     double restock = 0;
     total = cdCopies * cdPrice;
     restock = total * .05;
return restock;
// New output method overrides superclass's output method with new data and format.
     public String toString() {
          return String.format("SKU: %2d     Genre: %-12s     Name: %-20s     \nPrice: $%6.2f Value: $%,8.2f Stock: %3d      Restocking Fee: $%6.2f\n",
cdSku, genre , cdName, cdPrice, totalValue(), cdCopies, restockFee());
}// Ends CDWithGenre class

Answer 1

Hey Michael,
I edited the code to add some more features but I am having some errors. Can you help again?
Here is the code
The additional buttons are for features I need to add. The commented part that says save need to save to a certain location.
But the problem I am having is with the previous and next buttons. I need them to loop so when Next reaches the end of the array it needs to go to the first element again and keep on rolling thru. The previous needs to roll back from element 0 to the end again.
This works when the program is not stopped on the last or first element. If I press the last button then press next, it errors. If I press the first button and press previous, it errors.
I also need to add an icon
Let me know what you think. Thanks a bunch
class InventoryGUI
  Inventory inventory;
  int displayElement = 0;
  public InventoryGUI(Inventory inv)
    inventory = inv;
  public void buildGUI()
    final JTextArea textArea = new JTextArea(inventory.display(displayElement));
    final JButton prevBtn = new JButton("Previous"); 
    final JButton nextBtn = new JButton("Next");   
    final JButton lastBtn = new JButton("Last");
    final JButton firstBtn = new JButton("First");
    final JButton addBtn = new JButton("Add"); 
    final JButton modifyBtn = new JButton("Modify");   
    final JButton searchBtn = new JButton("Search");
    final JButton deleteBtn = new JButton("Delete");
    final JButton saveBtn = new JButton("Save");
    ImageIcon icon = new ImageIcon("images/icon.jpg");  
    JLabel label1 = new JLabel(icon);
    JPanel panel = new JPanel(new GridLayout(2,4));
    panel.add(firstBtn); panel.add(nextBtn); panel.add(prevBtn); panel.add(lastBtn);
    panel.add(addBtn); panel.add(modifyBtn); panel.add(searchBtn); panel.add(deleteBtn);
    //panel.add(saveBtn);
    JFrame invFrame = new JFrame();   
    invFrame.getContentPane().add(new JScrollPane(textArea),BorderLayout.CENTER);
    invFrame.getContentPane().add(panel,BorderLayout.SOUTH);
    invFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    invFrame.pack();
    invFrame.setSize(500,200);
    invFrame.setTitle("Inventory Manager");
    invFrame.setLocationRelativeTo(null);
    invFrame.setVisible(true);
    prevBtn.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        nextBtn.setEnabled(true);
        displayElement--;
        textArea.setText(inventory.display(displayElement));
        if(displayElement <= 0) displayElement = 5;
    nextBtn.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        prevBtn.setEnabled(true);
        displayElement++;
        textArea.setText(inventory.display(displayElement));
        if(displayElement >= inventory.nCount-1) displayElement = -1;
    firstBtn.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        firstBtn.setEnabled(true);
        displayElement = 0;
        textArea.setText(inventory.display(displayElement));
    lastBtn.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        lastBtn.setEnabled(true);
        displayElement = inventory.nCount-1;
        textArea.setText(inventory.display(displayElement));
}