The date spinner is synchronized with the day, month, and year spinners in Spinn

Question

The date spinner is synchronized with the day, month, and year spinners in SpinnerModelEditorDemo.java.

import javax.swing.*;
import javax.swing.event.*;
import java.util.*;
import java.text.*;
import java.awt.*;

public class SpinnerModelEditorDemo extends JApplet {
// Create four spinners for date, day, month, and year
private JSpinner jspDate =
    new JSpinner(new SpinnerDateModel());
private JSpinner jspDay =
    new JSpinner(new SpinnerNumberModel(1, 1, 31, 1));
private String[] monthNames = new DateFormatSymbols().getMonths();
private JSpinner jspMonth = new JSpinner
    (new SpinnerListModel(Arrays.asList(monthNames).subList(0, 12)));
private JSpinner spinnerYear =
    new JSpinner(new SpinnerNumberModel(2004, 1, 3000, 1));

public SpinnerModelEditorDemo() {
    // Group labels
    JPanel panel1 = new JPanel();
    panel1.setLayout(new GridLayout(4, 1));
    panel1.add(new JLabel("Date"));
    panel1.add(new JLabel("Day"));
    panel1.add(new JLabel("Month"));
    panel1.add(new JLabel("Year"));

    // Group spinners
    JPanel panel2 = new JPanel();
    panel2.setLayout(new GridLayout(4, 1));
    panel2.add(jspDate);
    panel2.add(jspDay);
    panel2.add(jspMonth);
    panel2.add(spinnerYear);

    // Add spinner and label to the UI
    add(panel1, BorderLayout.WEST);
    add(panel2, BorderLayout.CENTER);

    // Set editor for date
    JSpinner.DateEditor dateEditor =
      new JSpinner.DateEditor(jspDate, "MMM dd, yyyy");
    jspDate.setEditor(dateEditor);

    // Set editor for year
    JSpinner.NumberEditor yearEditor =
      new JSpinner.NumberEditor(spinnerYear, "####");
    spinnerYear.setEditor(yearEditor);

    // Update date to synchronize with the day, month, and year
    updateDate();

    // Register and create a listener for jspDay
    jspDay.addChangeListener(new ChangeListener() {
      public void stateChanged(javax.swing.event.ChangeEvent e) {
        updateDate();
      }
    });

    // Register and create a listener for jspMonth
    jspMonth.addChangeListener(new ChangeListener() {
      public void stateChanged(javax.swing.event.ChangeEvent e) {
        updateDate();
      }
    });

    // Register and create a listener for spinnerYear
    spinnerYear.addChangeListener(new ChangeListener() {
      public void stateChanged(javax.swing.event.ChangeEvent e) {
        updateDate();
      }
    });
}

/** Update date spinner to synchronize with the other spinners */
private void updateDate() {
    // Get current month and year in int
    int month = ((SpinnerListModel)jspMonth.getModel()).
        getList().indexOf(jspMonth.getValue());
    int year = ((Integer)spinnerYear.getValue()).intValue();

    // Set a new maximum number of days for the new month and year
    SpinnerNumberModel numberModel =
      (SpinnerNumberModel)jspDay.getModel();
    numberModel.setMaximum(new Integer(maxDaysInMonth(year, month)));

    // Set a new current day if it exceeds the maximum
    if (((Integer)(numberModel.getValue())).intValue() >
        maxDaysInMonth(year, month))
      numberModel.setValue(new Integer(maxDaysInMonth(year, month)));

    // Get the current day
    int day = ((Integer)jspDay.getValue()).intValue();

    // Set a new date in the date spinner
    jspDate.setValue(
      new GregorianCalendar(year, month, day).getTime());
}

/** Return the maximum number of days in a month. For example,
    Feb 2004 has 29 days. */
private int maxDaysInMonth(int year, int month) {
    Calendar calendar = new GregorianCalendar(year, month, 1);
    return calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
}

public static void main(String[] args) {
    javax.swing.JFrame frame = new javax.swing.JFrame(
        "SpinnerModelEditorDemo");

    SpinnerModelEditorDemo applet = new SpinnerModelEditorDemo();

    // Add the applet instance to the frame
    frame.getContentPane().add(applet, java.awt.BorderLayout.CENTER);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    // Invoke init and start
    applet.init();
    applet.start();

    // Display the frame
    frame.pack();
    frame.setVisible(true);
}
}

Improve it to synchronize the day, month, and year spinners with the date spinner. In other words, when a new value is selected in the date spinner, the values in the day, month, and year spinners are updated accordingly.

Explanation / Answer

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