Java Thread : I want to fade in and out the image but when I compile the image is not shown

Question

This is my code please help and explain what I did wrong thank you very much. Also I am a bit confuse about Thread whether I did correctly way.

public class Fade extends JPanel implements Runnable {

    static Image image;
    private float alpha = 0f;
    static JFrame frame;

    public static void main(String[] args) throws IOException {

        image = new ImageIcon(ImageIO.read(new File("gummybear.jpg")))
                .getImage();

        frame = new JFrame("fade frame");
        frame.add(new Fade());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(image.getWidth(frame), image.getHeight(frame));
        // set picture in the center of screen
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);

        ExecutorService executor = Executors.newFixedThreadPool(1);
        Runnable fade = new Fade();
        executor.execute(fade);

        // executor.shutdown();

        // while (!executor.isTerminated()) {
        // }
        // System.out.println("Finished fade in / fade out threads");

    }

    public void run() {

        while (alpha < 1) {
            try {
                System.out.println(alpha);
                alpha += 0.1f;
                this.repaint();

                Thread.sleep(100);
            } catch (InterruptedException ex) {
                Logger.getLogger(Fader.class.getName()).log(Level.SEVERE, null,
                        ex);
            }

        }

    }

    @Override
    public void paintComponent(Graphics g) {

        super.paintComponent(g);

        Graphics2D g2d = (Graphics2D) g;

        // SRC_OVER: If pixels in the source and the destination overlap, only
        // the source
        // pixels outside of the overlapping area are rendered. The pixels in
        // the overlapping area are not changed.

        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER,
                alpha));

        g2d.drawImage(image, 0, 0, null);

        // Color c = new Color(255, 255, 255, alpha);

        // g2d.setColor(c);

        // g2d.fillRect(0, 0, image.getWidth(frame), image.getHeight(frame));

        System.out.println("repaint");

    }

}

...............

*"I am a bit confuse about Thread whether I did correctly way."* No. Better to use a Swing `Timer` when calling methods like `repaint()`. That would obey the EDT (Event Dispatch Thread) rule which says GUI updates should be performed on the EDT. General tips: 1) For better help sooner, post an [MCVE](http://stackoverflow.com/help/mcve) (Minimal Complete and Verifiable Example). 2) One way to get image(s) for an example is to hot-link to the images seen in [this answer](http://stackoverflow.com/a/19209651/418556). — Andrew Thompson, Apr 17 '14 at 15:13

cyberbrain · Answer 1 · 2014-04-17T13:59:08.537

Image Stuff

It looks to me that you want to add transparency to an image that was loaded from a JPG file. JPG files don't have an alpha channel (that is used for transparency), so this will not work.

You find a good example for working with transparency (and loading images from JPG) in the one of the Java tutorials: Drawing an Image

There you find a nice example with code that does nearly what you want: change the transparency of an image loaded from a JPG file. The difference is that the opacity value is taken from a slider control instead of a timed variable.

Threading Stuff

Edit: I just realized, that you are using Swing, an API that is not designed to be thread safe.

I just have to point you to the Java Tutorials How to Use Swing Timers and Concurrency in Swing then.

Neither the fact that JPG does not support transparency, not the fact that Swing is not thread-safe is in *any* way related to this question. — Marco13, Apr 17 '14 at 14:20

score 1 · Accepted Answer · answered Apr 17 '14 at 14:23

The problem is that you are not changing the alpha value. At least, not the alpha value of the Fade instance that you are showing:

// Here you are adding a "Fade" instance to the frame.
frame.add(new Fade());
...

// Here you are creating a NEW "Fade" instance. Only in 
// this instance, the alpha value will be affected
Runnable fade = new Fade();
executor.execute(fade);

Change this to

// Create a Fade instance and add it to the frame
Fade fade = new Fade();
frame.add(fade);
...

// Submit the SAME Fade instance to the executor
executor.execute(fade);

You'll also have to verify that the alpha value remains in [0,1], but this can be done with something like

alpha += 0.1f;
alpha = Math.min(1.0f, alpha);

Java Thread : I want to fade in and out the image but when I compile the image is not shown

2 Answers2

Image Stuff

Threading Stuff