Thread: Arrays, JButton, and Action Listener

Hi all,

I have this homework assignment that I'm having trouble with. I'm to create a shopping cart with a JCombo box that offers the buyer four items to choose from and quantity. The issue I'm having is programming the "Buy Button". I need it to keep a running tally of items selected for purchase. For example, if I select Item 1 from the JCombcoBox and click buy, then select item 2 and a different quantity and click buy it keeps a running total of both item 1 and item 2 etc. I'm not sure what to place in JButtonActionPerformed to accomplish this. It needs to output what I bought to the JTextArea as well as keep a running total. Also, how do I program the clear button? I dropped a JButton on the JFrameForm and add an action listener to it.

Here's what I have so far. I used a JFrameForm to create the GUI.

Can anyone point me in the right direction?

Here's the code I'm asking about:

    private void buyJButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           
        // TODO add your handling code here:
    }                                          
 
    private void clearJButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             
        // TODO add your handling code here:
    }                                            
 
    private void itemsJComboBoxItemStateChanged(java.awt.event.ItemEvent evt) {                                                
 
        int itemindex = itemsJComboBox.getSelectedIndex();
 
        priceJTextField.setText(String.valueOf(prices[itemindex]));
 
 
    }

And here's all my code:

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
 
/**
 *
 * @author info3000-stu02
 */
public class ShoppingCart extends javax.swing.JFrame {
 
    /**
     * Creates new form ShoppingCart
     */
    public ShoppingCart() {
        initComponents();
    }
 
    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {
 
        jLabel1 = new javax.swing.JLabel();
        jScrollPane1 = new javax.swing.JScrollPane();
        itemsBoughtJTextArea = new javax.swing.JTextArea();
        itemsJComboBox = new javax.swing.JComboBox();
        buyJButton = new javax.swing.JButton();
        jLabel2 = new javax.swing.JLabel();
        jLabel3 = new javax.swing.JLabel();
        jLabel4 = new javax.swing.JLabel();
        quantityJTextField = new javax.swing.JTextField();
        priceJTextField = new javax.swing.JTextField();
        totalJTextField = new javax.swing.JTextField();
        clearJButton = new javax.swing.JButton();
 
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
 
        jLabel1.setText("Item Bought");
 
        itemsBoughtJTextArea.setEditable(false);
        itemsBoughtJTextArea.setColumns(20);
        itemsBoughtJTextArea.setRows(5);
        jScrollPane1.setViewportView(itemsBoughtJTextArea);
 
        itemsJComboBox.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" }));
        itemsJComboBox.addItemListener(new java.awt.event.ItemListener() {
            public void itemStateChanged(java.awt.event.ItemEvent evt) {
                itemsJComboBoxItemStateChanged(evt);
            }
        });
 
        buyJButton.setText("Buy");
        buyJButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                buyJButtonActionPerformed(evt);
            }
        });
 
        jLabel2.setText("Quantity");
 
        jLabel3.setText("Price");
 
        jLabel4.setText("Total");
 
        quantityJTextField.setHorizontalAlignment(javax.swing.JTextField.RIGHT);
        quantityJTextField.setText("0");
 
        priceJTextField.setEditable(false);
        priceJTextField.setHorizontalAlignment(javax.swing.JTextField.RIGHT);
 
        totalJTextField.setEditable(false);
        totalJTextField.setHorizontalAlignment(javax.swing.JTextField.RIGHT);
 
        clearJButton.setText("Clear");
        clearJButton.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                clearJButtonActionPerformed(evt);
            }
        });
 
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                    .addGroup(layout.createSequentialGroup()
                        .addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                        .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 172, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addGroup(layout.createSequentialGroup()
                                .addGap(18, 18, 18)
                                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                                    .addGroup(layout.createSequentialGroup()
                                        .addComponent(itemsJComboBox, javax.swing.GroupLayout.PREFERRED_SIZE, 129, javax.swing.GroupLayout.PREFERRED_SIZE)
                                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                                        .addComponent(priceJTextField, javax.swing.GroupLayout.PREFERRED_SIZE, 92, javax.swing.GroupLayout.PREFERRED_SIZE))
                                    .addGroup(layout.createSequentialGroup()
                                        .addComponent(buyJButton, javax.swing.GroupLayout.PREFERRED_SIZE, 78, javax.swing.GroupLayout.PREFERRED_SIZE)
                                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                                        .addComponent(clearJButton, javax.swing.GroupLayout.PREFERRED_SIZE, 92, javax.swing.GroupLayout.PREFERRED_SIZE))))
                            .addGroup(layout.createSequentialGroup()
                                .addGap(272, 272, 272)
                                .addComponent(jLabel4))))
                    .addGroup(javax.swing.GroupLayout.Alignment.LEADING, layout.createSequentialGroup()
                        .addGap(23, 23, 23)
                        .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 91, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGap(332, 332, 332)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addGroup(layout.createSequentialGroup()
                                .addGap(14, 14, 14)
                                .addComponent(jLabel2)
                                .addGap(102, 102, 102)
                                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                                    .addComponent(jLabel3)
                                    .addComponent(totalJTextField, javax.swing.GroupLayout.PREFERRED_SIZE, 52, javax.swing.GroupLayout.PREFERRED_SIZE)))
                            .addComponent(quantityJTextField, javax.swing.GroupLayout.PREFERRED_SIZE, 71, javax.swing.GroupLayout.PREFERRED_SIZE))))
                .addContainerGap(229, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addGap(35, 35, 35)
                        .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 27, javax.swing.GroupLayout.PREFERRED_SIZE))
                    .addGroup(layout.createSequentialGroup()
                        .addGap(33, 33, 33)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                            .addComponent(jLabel2)
                            .addComponent(jLabel3))))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 285, javax.swing.GroupLayout.PREFERRED_SIZE)
                    .addGroup(layout.createSequentialGroup()
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                            .addComponent(itemsJComboBox, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                                .addComponent(quantityJTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(priceJTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)))
                        .addGap(150, 150, 150)
                        .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                            .addComponent(jLabel4)
                            .addComponent(totalJTextField, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))))
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(buyJButton)
                    .addComponent(clearJButton))
                .addGap(102, 102, 102))
        );
 
        pack();
    }// </editor-fold>                        
 
    private void buyJButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           
        // TODO add your handling code here:
    }                                          
 
    private void clearJButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             
        // TODO add your handling code here:
    }                                            
 
    private void itemsJComboBoxItemStateChanged(java.awt.event.ItemEvent evt) {                                                
 
        int itemindex = itemsJComboBox.getSelectedIndex();
 
        priceJTextField.setText(String.valueOf(prices[itemindex]));
 
 
    }                                               
 
    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(ShoppingCart.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(ShoppingCart.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(ShoppingCart.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(ShoppingCart.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>
 
        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new ShoppingCart().setVisible(true);
            }
        });
    }
 
    private double prices[] = {1.25, 1.75, 2.93,5.45,2.09};
    // Variables declaration - do not modify                     
    private javax.swing.JButton buyJButton;
    private javax.swing.JButton clearJButton;
    private javax.swing.JTextArea itemsBoughtJTextArea;
    private javax.swing.JComboBox itemsJComboBox;
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel jLabel3;
    private javax.swing.JLabel jLabel4;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTextField priceJTextField;
    private javax.swing.JTextField quantityJTextField;
    private javax.swing.JTextField totalJTextField;
    // End of variables declaration                   
}

Ok....I've looked at it some more and I'm still not getting it.

What I need to do is have the buyJButton get the name of the item, price selected in the drop down menu (JComboBox) and multiply the quantity times the price of the item and write that to the totalJTextField as well as to the JTextArea. I've tried several things and I can't get it to work.

private void buyJButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           
 
        int itemindex = itemsJComboBox.getSelectedIndex();
 
        int total = itemsJComboBox.getSelectedIndex * quantity;

getSelectedIndex() returns the index of the selected item. In other words, the 5th item in the JComboBox might be 20.00. getSelectedIndex() returns '4' (the 5th item), not 20.00. Review the JComboBox methods to determine which method will return what you're after. Note the TYPE of the item returned so that you apply any necessary casting or parsing before trying to use it.

THank you. I've got it mostly figured out. The only problem I'm still having is writing to my itemsBoughtJTextArea. I want to write to it what has been bought. Also, I'm not sure where to start on coding my clearJButton to reset everything.

private void buyJButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           
 
        int itemindex = itemsJComboBox.getSelectedIndex();
 
        int quantity = Integer.parseInt(quantityJTextField.getText());
 
      totalJTextField.setText(String.valueOf(prices[itemindex] * quantity)); 
 
      itemsBoughtJTextArea.setText(itemsJComboBox());

Different components have different ways to clear them. If the component has a setText() method, you can clear by calling theComponent.setText( "" ); // empty quotes. If you've provided a blank item in your JComboBox list of items (usually at index 0), you can set the JComboBox to show index 0, or whatever index shows the blank item. Check the API for each component's methods to determine the appropriate method to do what you want.

Thanks, I got that working. Any thoughts on printing to the jTextArea the item name and purchase price?

I've tried this but it does not work:

itemsBoughtJTextArea.append("\n"+JComboBox.getSelectedIndex());

It prints 1. I'm guessing that's the item 1 in the index.

Yes, you're collecting and printing the selected index. You want the item at the index, not the index itself.