Hi, I've been staring at this for a long time and don't see the error, whenever I hit a number it gives me the error below the code:
import javax.swing.*;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JMenu;
import javax.swing.JPanel;
import javax.swing.JMenuItem;
import javax.swing.JTextField;
import java.awt.*;
import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.Color;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
public class Calculator extends JFrame
{
public static final int WIDTH = 500;
public static final int HEIGHT = 500;
private JPanel textPanel;
private JPanel numbersPanel;
private JPanel operandsPanel;
private JTextField textField;
private class MenuListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
textField.setText("0");
}
}
private class NumbersListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
String buttonString = e.getActionCommand();
if (buttonString.equals("1"))
textField.setText("1");
if (buttonString.equals("2"))
textField.setText("2");
if (buttonString.equals("3"))
textField.setText("3");
if (buttonString.equals("4"))
textField.setText("4");
if (buttonString.equals("5"))
textField.setText("5");
if (buttonString.equals("6"))
textField.setText("6");
if (buttonString.equals("7"))
textField.setText("7");
if (buttonString.equals("8"))
textField.setText("8");
if (buttonString.equals("9"))
textField.setText("9");
if (buttonString.equals("0"))
textField.setText("0");
}
}
private class OperandsListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
}
}
public static void main(String[] args)
{
Calculator gui = new Calculator();
gui.setVisible(true);
}
public Calculator()
{
super(); //invokes the JFrame constructor.
setSize(WIDTH,HEIGHT);
setTitle("Calculator");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //default exit on close
JMenu menu = new JMenu("Options");
JMenuItem clear = new JMenuItem("Clear");
clear.addActionListener(new MenuListener());
menu.add(clear);
JPanel textPanel = new JPanel();
JTextField textField = new JTextField("0", 20);
textPanel.add(textField);
JPanel numbersPanel = new JPanel();
numbersPanel.setLayout(new GridLayout(4,3));
JButton oneButton = new JButton("One");
oneButton.setBackground(Color.GRAY);
numbersPanel.add(oneButton);
oneButton.addActionListener(new NumbersListener());
JButton twoButton = new JButton("2");
twoButton.setBackground(Color.GRAY);
numbersPanel.add(twoButton);
twoButton.addActionListener(new NumbersListener());
JButton threeButton = new JButton("3");
threeButton.setBackground(Color.GRAY);
numbersPanel.add(threeButton);
threeButton.addActionListener(new NumbersListener());
JButton fourButton = new JButton("4");
fourButton.setBackground(Color.GRAY);
numbersPanel.add(fourButton);
fourButton.addActionListener(new NumbersListener());
JButton fiveButton = new JButton("5");
fiveButton.setBackground(Color.GRAY);
numbersPanel.add(fiveButton);
fiveButton.addActionListener(new NumbersListener());
JButton sixButton = new JButton("6");
sixButton.setBackground(Color.GRAY);
numbersPanel.add(sixButton);
sixButton.addActionListener(new NumbersListener());
JButton sevenButton = new JButton("7");
sevenButton.setBackground(Color.GRAY);
numbersPanel.add(sevenButton);
sevenButton.addActionListener(new NumbersListener());
JButton eightButton = new JButton("8");
eightButton.setBackground(Color.GRAY);
numbersPanel.add(eightButton);
eightButton.addActionListener(new NumbersListener());
JButton nineButton = new JButton("9");
nineButton.setBackground(Color.GRAY);
numbersPanel.add(nineButton);
nineButton.addActionListener(new NumbersListener());
JButton zeroButton = new JButton("0");
zeroButton.setBackground(Color.GRAY);
numbersPanel.add(zeroButton);
zeroButton.addActionListener(new NumbersListener());
JPanel operandsPanel = new JPanel();
operandsPanel.setLayout(new GridLayout(4,1));
JButton timesButton = new JButton("*");
operandsPanel.add(timesButton);
timesButton.setBackground(Color.LIGHT_GRAY);
timesButton.addActionListener(new OperandsListener());
JButton divideButton = new JButton("/");
operandsPanel.add(divideButton);
divideButton.setBackground(Color.LIGHT_GRAY);
divideButton.addActionListener(new OperandsListener());
JButton subtractButton = new JButton("-");
operandsPanel.add(subtractButton);
subtractButton.setBackground(Color.LIGHT_GRAY);
subtractButton.addActionListener(new OperandsListener());
JButton addButton = new JButton("+");
operandsPanel.add(addButton);
addButton.setBackground(Color.LIGHT_GRAY);
addButton.addActionListener(new OperandsListener());
add(textPanel, BorderLayout.NORTH);
add(numbersPanel, BorderLayout.CENTER);
add(operandsPanel, BorderLayout.EAST);
add(menu, BorderLayout.WEST);
}
}
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Calculator$NumbersListener.actionPerformed(Calculator.java:55)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6038)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3260)
at java.awt.Component.processEvent(Component.java:5803)
at java.awt.Container.processEvent(Container.java:2058)
at java.awt.Component.dispatchEventImpl(Component.java:4410)
at java.awt.Container.dispatchEventImpl(Container.java:2116)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
at java.awt.Container.dispatchEventImpl(Container.java:2102)
at java.awt.Window.dispatchEventImpl(Window.java:2429)
at java.awt.Component.dispatchEvent(Component.java:4240)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
