Help with GUI program

Question

Writing a program that uses menu options of ADD, SUBTRACT, MULTIPLY, and DIVIDE.
The user enters a number in a field labeled "Number 1" then enters a number in a field labeled "Number 2". The final field is labeled "Result"
Each of the menu options has an ActionEvent.
I'm having trouble with how to get the fields for Number 1 and Number 2 to display in the Result field when the user selects one of the menu options.
Here is the code with an ActionEvent started for "Add" but not finished since I neeed some advice from this point on....
Please disregard the other menu options, at this point I am just working on the math portion...
Cheers!
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Brown7 extends JFrame implements ActionListener
public static final int WIDTH = 400;
public static final int HEIGHT = 200;
private JTextField inputField, inputsecondField, resultField;
private double sum = 0;
private double difference = 0;
private double product = 0;
private double quotient = 0;
public Brown7()
setSize (WIDTH, HEIGHT);
addWindowListener(new WindowDestroyer());
setTitle ("Menu Demo");
Container contentPane = getContentPane();
contentPane.setLayout(new BorderLayout());
JPanel buttonPanel = new JPanel();
buttonPanel.setLayout(new FlowLayout());
JButton sumbutton = new JButton("Add");
sumbutton.addActionListener(this);
buttonPanel.add(sumbutton);
JButton subbutton = new JButton("Subtraction");
subbutton.addActionListener(this);
buttonPanel.add(subbutton);
JButton multbutton = new JButton("Multiply");
multbutton.addActionListener(this);
buttonPanel.add(multbutton);
JButton divbutton = new JButton("Divide");
divbutton.addActionListener(this);
buttonPanel.add(divbutton);
contentPane.add(buttonPanel, BorderLayout.SOUTH);
JPanel infoPanel = new JPanel();
infoPanel.setLayout(new FlowLayout());
JLabel nameLabel = new JLabel("Number 1");
infoPanel.add(nameLabel);
inputField = new JTextField("", 3);
infoPanel.add(inputField);
JLabel secondnameLabel = new JLabel("Number 2");
infoPanel.add(secondnameLabel);
inputsecondField = new JTextField("", 3);
infoPanel.add(inputsecondField);
JLabel resultLabel = new JLabel("Result");
infoPanel.add(resultLabel);
resultField = new JTextField("", 5);
infoPanel.add(resultField);
contentPane.add(infoPanel);
JMenuBar mBar = new JMenuBar();
setJMenuBar(mBar);
JMenu operationsMenu = new JMenu("Operations");
mBar.add(operationsMenu);
JMenuItem o;
o = new JMenuItem("Add");
o.addActionListener(this);
operationsMenu.add(o);
o = new JMenuItem("Subtract");
o.addActionListener(this);
operationsMenu.add(o);
o = new JMenuItem("Multiply");
o.addActionListener(this);
operationsMenu.add(o);
o = new JMenuItem("Divide");
o.addActionListener(this);
operationsMenu.add(o);
JMenu viewMenu = new JMenu("View");
mBar.add(viewMenu);
JMenuItem v;
v = new JMenuItem("Metal");
v.addActionListener(this);
viewMenu.add(v);
v = new JMenuItem("Motif");
v.addActionListener(this);
viewMenu.add(v);
v = new JMenuItem("Windows");
v.addActionListener(this);
viewMenu.add(v);
JMenu exitMenu = new JMenu("Exit");
mBar.add(exitMenu);
JMenuItem e;
e = new JMenuItem("Close");
e.addActionListener(this);
exitMenu.add(e);
public void actionPerformed(ActionEvent e)
if (e.getActionCommand().equals("Close"))
System.exit(0);
else if (e.getActionCommand().equals("Add"))
else
System.out.println("Error in Brown7 interface.");
public static void main(String[] args)
Brown7 gui = new Brown7();
gui.setVisible(true);

Answer 1

You can use a JOptionPane for the textfield input. Here I used a DocumentFilter (new in JDK1.4). It allows only specified characters to be entered and beeps for illegal characters. If you still want a message dialog you can add it in the document filter class with (or in place of) the Toolkit..beep call.
I also changed the variable result to a double and added a NumberFormat to allow formatting to only one decimal place for fractions (as a result of division) in resultField.
I gave a choice of YES_NO vs. YES_NO_CANCEL options in the exit dialog.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.text.NumberFormat;    // new
import javax.swing.text.*;        // new
public class BrownTest extends JFrame implements ActionListener
    public static final int WIDTH = 400;
    public static final int HEIGHT = 200;
    private JTextField inputField, inputsecondField, resultField;
    private double sum = 0;
    private double difference = 0;
    private double product = 0;
    private double quotient = 0;
    NumberFormat nf;
    JFrame frame = this;
    public BrownTest()
        nf = NumberFormat.getInstance();
        nf.setMaximumFractionDigits(1);
        setSize (WIDTH, HEIGHT);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setTitle ("Menu Demo");
        Container contentPane = getContentPane();
        contentPane.setLayout(new BorderLayout());
        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new FlowLayout());
        JButton sumbutton = new JButton("Add");
        sumbutton.addActionListener(this);
        buttonPanel.add(sumbutton);
        JButton subbutton = new JButton("Subtract");
        subbutton.addActionListener(this);
        buttonPanel.add(subbutton);
        JButton multbutton = new JButton("Multiply");
        multbutton.addActionListener(this);
        buttonPanel.add(multbutton);
        JButton divbutton = new JButton("Divide");
        divbutton.addActionListener(this);
        buttonPanel.add(divbutton);
        contentPane.add(buttonPanel, BorderLayout.SOUTH);
        JPanel infoPanel = new JPanel();
        infoPanel.setLayout(new FlowLayout());
        JLabel nameLabel = new JLabel("Number 1");
        infoPanel.add(nameLabel);
        inputField = new JTextField("", 3);
        infoPanel.add(inputField);
        JLabel secondnameLabel = new JLabel("Number 2");
        infoPanel.add(secondnameLabel);
        inputsecondField = new JTextField("", 3);
        infoPanel.add(inputsecondField);
        JLabel resultLabel = new JLabel("Result");
        infoPanel.add(resultLabel);
        resultField = new JTextField("", 5);
        infoPanel.add(resultField);
        // set document filter on textfield documents
        String integerDomain = "-.0123456789";
        FieldNumberFilter filter = new FieldNumberFilter(integerDomain);
        AbstractDocument doc = (AbstractDocument)inputField.getDocument();
        doc.setDocumentFilter(filter);
        doc = (AbstractDocument)inputsecondField.getDocument();
        doc.setDocumentFilter(filter);
        doc = (AbstractDocument)resultField.getDocument();
        doc.setDocumentFilter(filter);
        contentPane.add(infoPanel);
        JMenuBar mBar = new JMenuBar();
        setJMenuBar(mBar);
        JMenu operationsMenu = new JMenu("Operations");
        mBar.add(operationsMenu);
        JMenuItem o;
        o = new JMenuItem("Add");
        o.addActionListener(this);
        operationsMenu.add(o);
        o = new JMenuItem("Subtract");
        o.addActionListener(this);
        operationsMenu.add(o);
        o = new JMenuItem("Multiply");
        o.addActionListener(this);
        operationsMenu.add(o);
        o = new JMenuItem("Divide");
        o.addActionListener(this);
        operationsMenu.add(o);
        JMenu viewMenu = new JMenu("View");
        mBar.add(viewMenu);
        ViewMenuListener viewMenuListener = new ViewMenuListener();
        JMenuItem v;
        v = new JMenuItem("Metal");
        v.addActionListener(viewMenuListener);
        viewMenu.add(v);
        v = new JMenuItem("Motif");
        v.addActionListener(viewMenuListener);
        viewMenu.add(v);
        v = new JMenuItem("Windows");
        v.addActionListener(viewMenuListener);
        viewMenu.add(v);
        JMenu exitMenu = new JMenu("Exit");
        mBar.add(exitMenu);
        JMenuItem e;
        e = new JMenuItem("Close");
        e.addActionListener(this);
        exitMenu.add(e);
     * Listener for the Operations and Close menu items
    public void actionPerformed(ActionEvent e)
        String ac = e.getActionCommand();
        if (ac.equals("Close"))
            String message = "Are you sure you want to exit this program?";
            int returnVal = JOptionPane.showConfirmDialog(frame,
                                                          message,
                                                          "Exit Dialog",
            // either this */                             JOptionPane.YES_NO_OPTION,
            /* or this */                                 JOptionPane.YES_NO_CANCEL_OPTION,
                                                          JOptionPane.QUESTION_MESSAGE);
            if(returnVal == JOptionPane.CANCEL_OPTION ||
               returnVal == JOptionPane.CLOSED_OPTION)
                return;
            if(returnVal == JOptionPane.YES_OPTION)
                System.exit(0);
            if(returnVal == JOptionPane.NO_OPTION);
                frame.dispose();
        // read entered data
        String one = inputField.getText();
        String two = inputsecondField.getText();
        // if no entry, return
        if(one.equals("") || two.equals(""))
            return;
        // attempt to parse data
        double first, second;
        try
            first  = Double.parseDouble(one);
            second = Double.parseDouble(two);
        catch(NumberFormatException nfe)
            System.out.println(nfe.getMessage());
            return;
        // now we have good data, do calculations
        double result = 0;
        if (ac.equals("Add"))
            result = first + second;
        else if(ac.equals("Subtract"))
            result = first - second;
        else if(ac.equals("Multiply"))
            result = first * second;
        else if(ac.equals("Divide"))
            result = first / second;
        else
            System.out.println("Error in Brown7 interface.");
        resultField.setText(nf.format(result));
     * Listener for the View menu items
    private class ViewMenuListener implements ActionListener
        UIManager.LookAndFeelInfo[] info = UIManager.getInstalledLookAndFeels();
        public void actionPerformed(ActionEvent e)
            JMenuItem item = (JMenuItem)e.getSource();
            String ac = item.getActionCommand();
            String name = null;
            for(int i = 0; i < info.length; i++)
                if(info.getName().indexOf(ac) != -1)
name = info[i].getClassName();
if(name == null)
return;
try
UIManager.setLookAndFeel(name);
catch(ClassNotFoundException cnfe)
System.out.println(cnfe.getMessage());
catch(InstantiationException ie)
System.out.println(ie.getMessage());
catch(IllegalAccessException iae)
System.out.println(iae.getMessage());
catch(UnsupportedLookAndFeelException ulafe)
System.out.println(ulafe.getMessage());
SwingUtilities.updateComponentTreeUI(BrownTest.this);
public static void main(String[] args)
BrownTest gui = new BrownTest();
gui.setVisible(true);
* Document filter for input validation in textfields
class FieldNumberFilter extends DocumentFilter
String allowables;
public FieldNumberFilter(String legalCharacters) {
allowables = legalCharacters;
public void insertString(DocumentFilter.FilterBypass fb,
int offset,
String str,
AttributeSet attr) throws BadLocationException {
replace(fb, offset, 0, str, attr);
public void replace(DocumentFilter.FilterBypass fb,
int offset,
int length,
String str,
AttributeSet attrs) throws BadLocationException {
char[] source = str.toCharArray();
char[] result = new char[source.length];
int j = 0;
for(int i = 0; i < result.length; i++)
if(allowables.indexOf(source[i]) != -1)
result[j++] = source[i];
else
Toolkit.getDefaultToolkit().beep();
fb.replace(offset, length, new String(result, 0, j), attrs);