Question

I’m learning about change listeners and would like to find out why a part of my coding is not making a change listener fire when the user moves a slider.

Here is the listener. Everything is in the same method:

ChangeListener lst = new ChangeListener() {
    public void stateChanged(ChangeEvent e) {
        showDate();
    }
};

Here is some code that adds the listener:

m_slDay = new JSlider(JSlider.HORIZONTAL, 1, maxDays,
    m_calendar.get(Calendar.DAY_OF_MONTH));
m_slDay.setPaintLabels(true);
m_slDay.setMajorTickSpacing(5);
m_slDay.setMinorTickSpacing(1);
m_slDay.setPaintTicks(true);

// This line of code seems to work.  
m_slDay.addChangeListener(lst);

p = new JPanel();
p.setBorder(new TitledBorder(new EtchedBorder(), "Day"));
p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS));
p.add(Box.createRigidArea(RIGID_DIMENSION));
p.add(m_slDay);
p.add(Box.createRigidArea(RIGID_DIMENSION));
p1.add(p);

This code is based on the above chunk of code but nothing happens when the user moves the slider:

m_slDayOfWeek = new JSlider(JSlider.HORIZONTAL, 1, maxDaysOfTheWeek,
    m_calendar.get(Calendar.DAY_OF_WEEK));
m_slDayOfWeek.setPaintLabels(true);
m_slDayOfWeek.setMajorTickSpacing(1);
m_slDayOfWeek.setMinorTickSpacing(1);
m_slDayOfWeek.setPaintTicks(true);

// This one is not working and I'm not sure why it's happening.
m_slDayOfWeek.addChangeListener(lst);

p = new JPanel();
p.setBorder(new TitledBorder(new EtchedBorder(), "Day of Week"));
p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS));
p.add(Box.createRigidArea(RIGID_DIMENSION));
p.add(m_slDayOfWeek);
p.add(Box.createRigidArea(RIGID_DIMENSION));
p1.add(p);

Answer 1

Seems like there is something wrong in your code part, as pointed out in comments in your showDate() method, this thing works flawlessly in this code :

import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class SliderChangeEffect extends JFrame
{
    private JSlider slider;
    private int count = 0;
    private ChangeListener changeListener = new ChangeListener()
    {
        public void stateChanged(ChangeEvent ce)
        {
            System.out.println(count++);
        }
    };

    private void createAndDisplayGUI()
    {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationByPlatform(true);

        JPanel contentPane = new JPanel();
        contentPane.setOpaque(true);

        slider = new JSlider(0, 10, 5);
        slider.setMajorTickSpacing(2);
        slider.setMinorTickSpacing(1);
        slider.addChangeListener(changeListener);

        contentPane.add(slider);

        getContentPane().add(contentPane);
        pack();
        setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new SliderChangeEffect().createAndDisplayGUI();
            }
        });
    }
}