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Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:1031)
at java.awt.Container.add(Container.java:352)
at PaymentPanel.<init>(PaymentApp.java:75)
at PaymentFrame.<init>(PaymentApp.java:22)
at PaymentApp.main(PaymentApp.java:10)
My Code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class PaymentApp
{
public static void main(String[] args)
{
JFrame frame = new PaymentFrame();
frame.setVisible(true);
}
}
class PaymentFrame extends JFrame
{
public PaymentFrame()
{
setTitle("Payment Application");
setResizable(false);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new PaymentPanel();
this.add(panel);
this.pack();
centerWindow(this);
}
private void centerWindow(Window w)
{
Toolkit tk = Toolkit.getDefaultToolkit();
Dimension d = tk.getScreenSize();
setLocation((d.width-w.getWidth())/2, (d.height-w.getHeight())/2);
}
}
class PaymentPanel extends JPanel implements ActionListener
{
private JRadioButton creditCardRadioButton,
billCustomerRadioButton;
private JTextField cardNumberTextField;
private JLabel cardTypeLabel,
cardNumberLabel,
expirationDateLabel;
private JButton acceptButton,
exitButton;
private JComboBox year,
month;
private JCheckBox verifiedCheckBox;
private JList cardTypeList;
public PaymentPanel()
{
setLayout(new GridBagLayout());
Border loweredBorder = BorderFactory.createBevelBorder(BevelBorder.LOWERED);
// radio button panel
JPanel radioPanel = new JPanel();
ButtonGroup billingGroup = new ButtonGroup();
radioPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
radioPanel.setBorder(
BorderFactory.createTitledBorder(loweredBorder, "Billing:"));
// credit card radio button
creditCardRadioButton = new JRadioButton("Credit card", true);
creditCardRadioButton.addActionListener(this);
billingGroup.add(creditCardRadioButton);
radioPanel.add(billCustomerRadioButton);
// bill customer radio button
billCustomerRadioButton = new JRadioButton("Bill customer");
billCustomerRadioButton.addActionListener(this);
billingGroup.add(billCustomerRadioButton);
radioPanel.add(billCustomerRadioButton);
add(radioPanel, getConstraints(0,0,3,1, GridBagConstraints.WEST));
// card type label
cardTypeLabel = new JLabel("Card type:");
add(cardTypeLabel, getConstraints(0,1,1,1, GridBagConstraints.EAST));
// card type list
String[] cardNames
= {"Visa", "Master Card", "American Express", "Other"};
JList cardTypeList = new JList(cardNames);
cardTypeList.setFixedCellWidth(170);
cardTypeList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
cardTypeList.setVisibleRowCount(3);
JScrollPane cardTypeScrollPane = new JScrollPane(cardTypeList);
add(cardTypeScrollPane,
getConstraints(1,1,2,1, GridBagConstraints.WEST));
// card number label
cardNumberLabel = new JLabel("Card number:");
add(cardNumberLabel,
getConstraints(0,2,1,1, GridBagConstraints.EAST));
// card number text field
cardNumberTextField = new JTextField(15);
add(cardNumberTextField, getConstraints(1,2,2,1, GridBagConstraints.WEST));
// expiration date label
expirationDateLabel = new JLabel("Expiration date:");
add(expirationDateLabel, getConstraints(0,3,1,1, GridBagConstraints.EAST));
// month combo box
String[] months = { "January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November",
"December" };
JComboBox month = new JComboBox(months);
add(month, getConstraints(1,3,1,1, GridBagConstraints.WEST));
// year Combo Box
String[] years = { "2005", "2006", "2007", "2008", "2009", "2010" };
JComboBox year = new JComboBox();
add(year, getConstraints(2,3,1,1, GridBagConstraints.WEST));
// verified check box
verifiedCheckBox = new JCheckBox("Verified");
add(verifiedCheckBox,
getConstraints(1,4,1,1, GridBagConstraints.WEST));
// accept button
acceptButton = new JButton("Accept");
acceptButton.addActionListener(this);
add(acceptButton, getConstraints(1,5,1,1, GridBagConstraints.EAST));
// exit button
exitButton = new JButton("Exit");
exitButton.addActionListener(this);
add(exitButton, getConstraints(2,5,1,1, GridBagConstraints.CENTER));
}
//Method for setting gridbag constraints
private GridBagConstraints getConstraints(int gridx, int gridy,
int gridwidth, int gridheight, int anchor)
{
GridBagConstraints c = new GridBagConstraints();
c.insets = new Insets(5, 5, 5, 5);
c.ipadx = 0;
c.ipady = 0;
c.gridx = gridx;
c.gridy = gridy;
c.gridwidth = gridwidth;
c.gridheight = gridheight;
c.anchor = anchor;
return c;
}
public void actionPerformed(ActionEvent e)
{
Object source = e.getSource();
if (source == exitButton)
System.exit(0);
else if (source == acceptButton)
{
String msg = "";
if (creditCardRadioButton.isSelected())
{
msg = "Bill " + (String)cardTypeList.getSelectedValue() +
"\nNumber + " + cardNumberTextField.getText() +
"\nExpiration date: " +
(String)month.getSelectedItem() +
", " + (String)year.getSelectedItem();
if (verifiedCheckBox.isSelected())
msg+= "\nCard has been verified,";
else
msg+= "\nCard has not been verified.";
}
else
msg = "Customer will be billed.";
JOptionPane.showMessageDialog(this, msg);
cardTypeList.setSelectedIndex(0);
cardNumberTextField.setText("");
month.setSelectedIndex(0);
year.setSelectedIndex(0);
verifiedCheckBox.setSelected(false);
}
else if (source == creditCardRadioButton
|| source == billCustomerRadioButton)
{
if (creditCardRadioButton.isSelected())
enableCreditCardControls(true);
else if (billCustomerRadioButton.isSelected())
enableCreditCardControls(false);
}
}
private void enableCreditCardControls(boolean enable)
{
cardTypeLabel.setEnabled(enable);
cardTypeList.setEnabled(enable);
cardNumberLabel.setEnabled(enable);
cardNumberTextField.setEnabled(enable);
expirationDateLabel.setEnabled(enable);
month.setEnabled(enable);
year.setEnabled(enable);
verifiedCheckBox.setEnabled(enable);
}
}
Mod edit - Please
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