[JAVA2D] Why am I getting a null pointer exception when I try to get the drawGraphics from a BufferStrategy?

[Ken Warner]

Environment: Java 1.5.0.12; Win2K SP4

Every once in a while, if I stop or restart the applet at just the wrong time
I see the following exception.  Line marked Here >> is the last code executed
in my stuff.  I check to see if the BufferStrategy is null before trying to
get a new drawGraphics.  It never says it's null.

It's annoying.  I didn't begin to get these errors until I recoded to use
the canonical render loop for BufferStrategy.

java.lang.NullPointerException
       at sun.java2d.SunGraphics2D.<init>(SunGraphics2D.java:213)
       at 
sun.awt.image.SunVolatileImage.createGraphics(SunVolatileImage.java:174)
       at java.awt.image.VolatileImage.getGraphics(VolatileImage.java:224)
       at 
java.awt.Component$BltBufferStrategy.getDrawGraphics(Component.java:3563)
Here >> at pancyl.PanCylCanvas.newPixels(PanCylCanvas.java:243)
       at pancyl.PanCylProjector.interpolateBC(PanCylProjector.java:749)
       at 
pancyl.PanCylProjector.setImageParametersAndPixels(PanCylProjector.java:316)
       at pancyl.PanCylImageFetch.run(PanCylImageFetch.java:418)
       at java.lang.Thread.run(Thread.java:595)

   private void checkBufferStrategy()
   {
       if(bs == null)
       {
           System.err.println("BUFFER STRATEGY NULL...");
           this.createBufferStrategy(2);
           bs = this.getBufferStrategy();
       }

   }
   private boolean DRAWATT = false;
   public void newPixels()
   {
       //System.err.println("newPixels()...");
       try
       {
           checkBufferStrategy();
           do {
               do {
Exception here ->   bg = (Graphics2D)bs.getDrawGraphics();     //this is line 
243
                   //System.err.println("Get BufferGraphics...");
                   mis.newPixels(pixels, cm, 0, thisW);
                   bg.drawImage(canvasImage, 0, 0, thisW, thisH, this);
                   if(DRAWATT)
                       drawAttribution();
                   bg.dispose();
                   //System.err.println("Dispose BufferGraphics...");
               } while (bs.contentsRestored());
               bs.show();
           } while (bs.contentsLost());
       }
       catch (Exception ie)
       {
           ie.printStackTrace();
       }
       this.requestFocusInWindow();
   }

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