CODEWITHSUNDEEP
javamultithreadingswingtimernullpointerexception
The Answer
The Answer

Reputation: 279

Java Timer synchronize with GUI

I'm trying to do an incremental display of a Component because it takes too much time to make all the calculations. So i don't want to freeze the graphic interface i'd like to display my image ( a fractal ) every 2.3 seconds. The function which calculate all the points is compute. Before i want to make the incremental display this method was calculating all points. Now it only calculates 10000 points.

class FlameBuilderPreviewComponent:

Timer timer1=new Timer(1000,new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e) {
            // TODO Auto-generated method stub
            time=time+10000;
            fa= builder.build().compute(density,frame,getWidth(),getHeight(),accumulator);

        }

    });
    timer1.start();
    for (int z = 0; z <fa.height(); z++) {
        for (int j = 0; j < fa.width(); j++) {
            image.setRGB(j,z,fa.color(palette, background, j, fa.height()-1-z).asPackedRGB());
        }
    }
    g0.drawImage(image,0,0,null);
    if (time>density*getWidth()*getHeight()){
        timer1.stop();
    }

Then the other part of the program is the GUI interface, i put another timer this one is responsible of repainting the image.

class FlameMakerGUI :

    fBPC=new FlameBuilderPreviewComponent(builder, background, palette, r1, density);
    Timer timer = new Timer(2500,new ActionListener(){
        public void actionPerformed(ActionEvent e) {
            fBPC.repaint();
            System.out.println("titi");
        }       
    });
    timer.start();
    fractale.add(fBPC,BorderLayout.CENTER);

Then this is the error that the program show each time timer is executed:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at ch.epfl.flamemaker.gui.FlameBuilderPreviewComponent.paintComponent(FlameBuilderPreviewComponent.java:82)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1512)
    at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1443)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1236)
    at javax.swing.JComponent._paintImmediately(JComponent.java:5169)
    at javax.swing.JComponent.paintImmediately(JComponent.java:4980)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:796)
    at javax.swing.RepaintManager$3.run(RepaintManager.java:784)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:784)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:757)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:706)
    at javax.swing.RepaintManager.access$1000(RepaintManager.java:62)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1651)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:727)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:688)
    at java.awt.EventQueue$3.run(EventQueue.java:686)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:697)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

Thank you for helping

Upvotes: 0

Views: 1137

Answers (1)

0x6C38
0x6C38

Reputation: 7076

You are creating a action listener every second, that doesn't make any sense. You obviously do not understand how event listeners work or how the Timer class works.

Also, tasks on the EDT (event dispatch thread) must finish quickly; if they don't, unhandled events back up and the user interface becomes unresponsive

You need to use Swing Worker in order to archive proper concurrency.

From the Oracle website:

Swing consists of three kinds of threads:

  • Initial threads, the threads that execute initial application code.

  • The event dispatch thread, where all event-handling code is executed. Most code that interacts with the Swing framework must also execute on this thread.

  • Worker threads, also known as background threads, where time-consuming background tasks are executed.

Upvotes: 1

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