Question

i have a mainFrame that contains panel. i want in this panel a thread that changes label image as long as the application is running…

when i created the panel that implements runnable, and then created an instance of this panel in the mainframe the application goes into infinite loop… my code as follows:

public mainFrame()
{
     BanerPanel baner = new BanerPanel();
     baner.run();
}

public class Banner_Panel extends JPanel implements Runnable {

    public Banner_Panel() {
        initComponents();
        imgPath = 2;
        imgLbl = new JLabel(new ImageIcon(getClass().getResource("/Photos/banner_4-01.png")));
        add(imgLbl);
        //run();
    }
    @Override
    public void run() {
        while(true)
        {
            try {
            while (true) {
                Thread.sleep(3000);
                switch(imgPath)
                {
                    case 1:
                        imgLbl.setIcon(new ImageIcon(getClass().getResource("/Photos/banner_4-01.png")));
                        imgPath = 2;
                        break;
                    case 2:
                        imgLbl.setIcon(new ImageIcon(getClass().getResource("/Photos/banner_1-01.png")));
                        imgPath = 3;
                        break;
                    case 3:
                        imgLbl.setIcon(new ImageIcon(getClass().getResource("/Photos/banner_2-01.png")));
                        imgPath = 4;
                        break;
                    case 4:
                        imgLbl.setIcon(new ImageIcon(getClass().getResource("/Photos/banner_3-01.png")));    
                        imgPath = 1;
                        break;
                }

            }
            } catch (InterruptedException iex) {}
        }
    }

Answer 1

• Don’t call JLabel#setIcon(...) in a background thread as this must be called on the Swing event thread or EDT. Instead, why not simply us a Swing Timer?
• Also, there’s no need to continually read in the image from the disk. Instead, read the images in once and place the ImageIcons in an array or ArrayList<ImageIcon> and simply iterate through the icons in your Swing Timer.
• Your code actually doesn’t use a background thread as you’re calling run() directly on your Runnable object which isn’t doing any threading at all. Please read the threading tutorial to see how to use Runnables and Threads (hint you call start() on the Thread).

For example

// LABEL_SWAP_TIMER_DELAY a constant int = 3000
javax.swing.Timer myTimer = new javax.swing.Timer(LABEL_SWAP_TIMER_DELAY, 
      new ActionListener(){
  private int timerCounter = 0;

  actionPerformed(ActionEvent e) {
    // iconArray is an array of ImageIcons that holds your four icons.
    imgLbl.setIcon(iconArray[timerCounter]);
    timerCounter++;
    timerCounter %= iconArray.length;
  }
});
myTimer.start();

For more, please check out the Swing Timer Tutorial.