Rollover on JLabel which consists of image within grid layout?

Question

I have a code with grid layout and two JLabel images. I wan't some text to appear everytime I roll over each image. I am familiar on how to do this when the image is not a JLabel, but have searched all over the web to find how to do this while it is an unnamed JLabel. The two images I wan't to have, with separate roll over messages are:

ImageIcon(getClass().getResource("giraffe.png"));
            Icon windows = new ImageIcon(getClass().getResource("windows.png"));

Here is my code:

    public class giraffe implements ActionListener{


        public void actionPerformed(ActionEvent event) {


            JOptionPane.showMessageDialog(null,
                    "Press ok, and see the amazing giraffe outside a window!");

            JDialog giraffewindow = new JDialog();
            Icon giraffe = new ImageIcon(getClass().getResource("giraffe.png"));
            Icon windows = new ImageIcon(getClass().getResource("windows.png"));

            giraffewindow.setLayout(new GridLayout(1, 2, 0, 0));
            giraffewindow.add(new JLabel (windows));
            giraffewindow.add(new JLabel (giraffe));


            giraffewindow.pack();
            giraffewindow.setTitle("GIRAFFE!");
            giraffewindow.setVisible(true);
            giraffewindow.setDefaultCloseOperation(DISPOSE_ON_CLOSE);

            /*
             * I want to have a rollover on EACH IMAGE so that when they rollover the image you see different text.
             */

        }

Thank you so much for the time you are taking for reading this, I really appreciate the effort you are putting into helping a fellow programmer!

Answer 1

Start by having a look at How to Write a Mouse Listener.

Basically, you want to attach a MouseListener to each label and monitor the mouseEntered and mouseExited events, updating the label state as per your requirements

import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            try {
                JLabel left = new JLabel(new ImageIcon(ImageIO.read(...))));
                left.setVerticalTextPosition(JLabel.BOTTOM);
                left.setHorizontalTextPosition(JLabel.CENTER);
                left.setHorizontalAlignment(JLabel.CENTER);
                left.setVerticalAlignment(JLabel.CENTER);
                left.setText(" ");
                JLabel right = new JLabel(new ImageIcon(ImageIO.read(...))));
                right.setVerticalTextPosition(JLabel.BOTTOM);
                right.setHorizontalTextPosition(JLabel.CENTER);
                right.setHorizontalAlignment(JLabel.CENTER);
                right.setVerticalAlignment(JLabel.CENTER);
                right.setText(" ");

                setLayout(new GridLayout(1, 2));

                add(left);
                add(right);

                left.addMouseListener(new MouseAdapter() {
                    @Override
                    public void mouseEntered(MouseEvent e) {
                        left.setText("I'm on the left");
                    }

                    @Override
                    public void mouseExited(MouseEvent e) {
                        left.setText(" ");
                    }
                });
                right.addMouseListener(new MouseAdapter() {
                    @Override
                    public void mouseEntered(MouseEvent e) {
                        right.setText("I'm on the right");
                    }

                    @Override
                    public void mouseExited(MouseEvent e) {
                        right.setText(" ");
                    }
                });
            } catch (IOException exp) {
                exp.printStackTrace();
            }
        }

    }

}

You might also want to have a look at Reading/Loading an Image

Answer 2

You can also create a generic listener by doing something like:

ImageIcon giraffe = new ImageIcon(...);
giraffe.setDescription("Giraffe Description");

Then your listener might look something like:

MouseListener ml = new MouseAdapter()
{
    @Override
    public void mouseEntered(MouseEvent e)
    {
        JLabel label = (JLabel)e.getSource();
        ImageIcon icon = (ImageIcon)label;
        label.setText( icon.getDescription() );
    }

    @Override
    public void mouseExited(MouseEvent e)
    {
        JLabel label = (JLabel)e.getSource();
        label.setText(" ");
    }
}

And you add the listener to the label:

JLabel giraffeLabel = new JLabel( giraffe );
giraffe.addMouseListener( ml );

The same listener can be used for your other JLabel because the event code knows with component generated the event.