Why am I getting this error: Exception in thread "AWT-EventQueue-0"?

Question

I am trying to create a flashing circle. I have got to the point where it changed once and then it throws and error Exception in thread "AWT-EventQueue-0 i have no idea why. can you help me? This is my code:

public class Final {
    private static JPanel contentPane;
    private static int cnt = 0;
    private static int counter =0;
    private static Color[] colours = {
        Color.ORANGE,
        Color.GRAY
    };

    public static void main(String args[]) {
        JFrame frame = new JFrame();
        frame.setSize(400, 525);
        frame.setLocationByPlatform(true);
        frame.setVisible(true);

        ActionListener actListner = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent event) {
                if (cnt == (colours.length)) {
                    cnt = 0;
                }
                frame.setBackground(colours[cnt++]);
                counter = cnt;
                System.out.println("Counter = "+cnt);
            }
        };

        contentPane = new JPanel() {
            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                g.setColor(colours[counter]);
                g.fillOval(160, 70, 50, 50);
            }
        };

        frame.add(contentPane);

        Timer timer = new Timer(500, actListner);
        timer.start();

    }
}

The full exception:

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: 2
    at Final$2.paintComponent(Final.java:56)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JComponent.paintToOffscreen(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
    at javax.swing.RepaintManager.paint(Unknown Source)
    at javax.swing.JComponent._paintImmediately(Unknown Source)
    at javax.swing.JComponent.paintImmediately(Unknown Source)
    at javax.swing.RepaintManager$4.run(Unknown Source)
    at javax.swing.RepaintManager$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.access$1300(Unknown Source)
    at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$400(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

"Exception in thread "AWT-EventQueue-0" You told us what thread the exception is in, but what is the exception itself? — nanofarad, Apr 19 '15 at 15:21
I already showed you how to increment the counter safely in your previous question! — Hovercraft Full Of Eels, Apr 19 '15 at 15:48

Hovercraft Full Of Eels · Answer 1 · 2015-04-19T15:47:17.030

1

You're incrementing your counter after checking its bounds, and then using it. Don't do that as that's the wrong order of things. Increment first, next check bounds and reset to 0 if need be, and only then use it.

// increment first, cnt++;, but not inline as you're doing it
cnt++; 
cnt %= colours.length; // mod it to make it 0 if greater than length
myColor = colours[cnt];  // then use it
repaint();

edited Apr 19 '15 at 15:47

answered Apr 19 '15 at 15:27

Hovercraft Full Of Eels

283,665
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373

score 0 · Answer 2 · answered Apr 19 '15 at 15:28

0

Simply change

if (cnt == (colours.length)){

to

if (cnt == (colours.length-1)){

answered Apr 19 '15 at 15:28

Blip

3,061
5
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50

it then doesnt reset to 0 after adding this. – user3077551 Apr 19 '15 at 15:32
are you saying this by seeing the output of line `System.out.println("Counter = "+cnt);`? – Blip Apr 19 '15 at 15:38
yea. but it just stays at one. i need it to cycle between 0-1 for it to cycle through the colors – user3077551 Apr 19 '15 at 15:53

Why am I getting this error: Exception in thread "AWT-EventQueue-0"?

2 Answers2