import java.awt.*;import java.awt.event.*;import javax.swing.*;import javax.swing.event.*;import javax.swing.text.*;import java.beans.PropertyChangeListener;import java.beans.PropertyChangeEvent;import java.text.*;/** * FormattedTextFieldDemo.java is a 1.4 example that * requires no other files. * * It implements a mortgage calculator that uses four * JFormattedTextFields. */public class FormattedTextFieldDemo extends JPanel                                    implements PropertyChangeListener {    //Values for the fields    private double amount = 100000;    private double rate = 7.5;  //7.5%    private int numPeriods = 30;    //Labels to identify the fields    private JLabel amountLabel;    private JLabel rateLabel;    private JLabel numPeriodsLabel;    private JLabel paymentLabel;    //Strings for the labels    private static String amountString = "Loan Amount: ";    private static String rateString = "APR (%): ";    private static String numPeriodsString = "Years: ";    private static String paymentString = "Monthly Payment: ";    //Fields for data entry    private JFormattedTextField amountField;    private JFormattedTextField rateField;    private JFormattedTextField numPeriodsField;    private JFormattedTextField paymentField;    //Formats to format and parse numbers    private NumberFormat amountFormat;    private NumberFormat percentFormat;    private NumberFormat paymentFormat;    public FormattedTextFieldDemo() {        super(new BorderLayout());        setUpFormats();        double payment = computePayment(amount,                                        rate,                                        numPeriods);        //Create the labels.        amountLabel = new JLabel(amountString);        rateLabel = new JLabel(rateString);        numPeriodsLabel = new JLabel(numPeriodsString);        paymentLabel = new JLabel(paymentString);        //Create the text fields and set them up.        amountField = new JFormattedTextField(amountFormat);        amountField.setValue(new Double(amount));        amountField.setColumns(10);        amountField.addPropertyChangeListener("value", this);        rateField = new JFormattedTextField(percentFormat);        rateField.setValue(new Double(rate));        rateField.setColumns(10);        rateField.addPropertyChangeListener("value", this);        numPeriodsField = new JFormattedTextField();        numPeriodsField.setValue(new Integer(numPeriods));        numPeriodsField.setColumns(10);        numPeriodsField.addPropertyChangeListener("value", this);        paymentField = new JFormattedTextField(paymentFormat);        paymentField.setValue(new Double(payment));        paymentField.setColumns(10);        paymentField.setEditable(false);        paymentField.setForeground(Color.red);        //Tell accessibility tools about label/textfield pairs.        amountLabel.setLabelFor(amountField);        rateLabel.setLabelFor(rateField);        numPeriodsLabel.setLabelFor(numPeriodsField);        paymentLabel.setLabelFor(paymentField);        //Lay out the labels in a panel.        JPanel labelPane = new JPanel(new GridLayout(0,1));        labelPane.add(amountLabel);        labelPane.add(rateLabel);        labelPane.add(numPeriodsLabel);        labelPane.add(paymentLabel);        //Layout the text fields in a panel.        JPanel fieldPane = new JPanel(new GridLayout(0,1));        fieldPane.add(amountField);        fieldPane.add(rateField);        fieldPane.add(numPeriodsField);        fieldPane.add(paymentField);        //Put the panels in this panel, labels on left,        //text fields on right.        setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));        add(labelPane, BorderLayout.CENTER);        add(fieldPane, BorderLayout.LINE_END);    }    /** Called when a field's "value" property changes. */    public void propertyChange(PropertyChangeEvent e) {        Object source = e.getSource();        if (source == amountField) {            amount = ((Number)amountField.getValue()).doubleValue();        } else if (source == rateField) {            rate = ((Number)rateField.getValue()).doubleValue();        } else if (source == numPeriodsField) {            numPeriods = ((Number)numPeriodsField.getValue()).intValue();        }        double payment = computePayment(amount, rate, numPeriods);        paymentField.setValue(new Double(payment));    }    /**     * Create the GUI and show it.  For thread safety,     * this method should be invoked from the     * event-dispatching thread.     */    private static void createAndShowGUI() {        //Make sure we have nice window decorations.        JFrame.setDefaultLookAndFeelDecorated(true);        //Create and set up the window.        JFrame frame = new JFrame("FormattedTextFieldDemo");        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        //Create and set up the content pane.        JComponent newContentPane = new FormattedTextFieldDemo();        newContentPane.setOpaque(true); //content panes must be opaque        frame.setContentPane(newContentPane);        //Display the window.        frame.pack();        frame.setVisible(true);    }    public static void main(String[] args) {        //Schedule a job for the event-dispatching thread:        //creating and showing this application's GUI.        javax.swing.SwingUtilities.invokeLater(new Runnable() {            public void run() {                createAndShowGUI();            }        });    }    //Compute the monthly payment based on the loan amount,    //APR, and length of loan.    double computePayment(double loanAmt, double rate, int numPeriods) {        double I, partial1, denominator, answer;        numPeriods *= 12;        //get number of months        if (rate > 0.01) {            I = rate / 100.0 / 12.0;         //get monthly rate from annual            partial1 = Math.pow((1 + I), (0.0 - numPeriods));            denominator = (1 - partial1) / I;        } else { //rate ~= 0            denominator = numPeriods;        }        answer = (-1 * loanAmt) / denominator;        return answer;    }    //Create and set up number formats. These objects also    //parse numbers input by user.    private void setUpFormats() {        amountFormat = NumberFormat.getNumberInstance();        percentFormat = NumberFormat.getNumberInstance();        percentFormat.setMinimumFractionDigits(3);        paymentFormat = NumberFormat.getCurrencyInstance();    }}