NullPointerException: component argument pData

Question

I keep getting this error message.
I am creating a screenManager, which sets a fullscreen displaymode based on the
available and compatible displaymodes on the system, and restores the original
displaymode upon exit. This is some new territory for me, and I have no idea where
and why this error appears. I'll post code if none can instantly tell what makes this
nullpointer exception appear.
Thanks,
Terje
java.lang.NullPointerException: component argument pData
at sun.awt.windows.Win32BackBufferSurfaceData.initSurface(Native Method)
at sun.awt.windows.Win32BackBufferSurfaceData.createData(Win32BackBuffer
SurfaceData.java:49)
at sun.awt.windows.Win32BackBuffer.createHWData(Win32BackBuffer.java:28)
at sun.awt.windows.WVolatileImage.initAcceleratedBackground(WVolatileIma
ge.java:100)
at sun.awt.windows.Win32BackBuffer.displayChanged(Win32BackBuffer.java:3
5)
at sun.awt.SunDisplayChanger.notifyListeners(SunDisplayChanger.java:102)
at sun.awt.Win32GraphicsEnvironment.displayChanged(Win32GraphicsEnvironm
ent.java:98)
at sun.awt.windows.WToolkit$4.run(WToolkit.java:734)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:178)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:454)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchTh
read.java:201)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)
Press any key to continue . . .

Answer 1

Well, I understand that much... The funny thing is the trace seems to be outside my code, and after running the application some more times, I occationally end up with the following message:
An unexpected exception has been detected in native code outside the VM.
Unexpected Signal : EXCEPTION_ACCESS_VIOLATION (0xc0000005) occurred at PC=0x2E57E76
Function=Java_sun_print_Win32PrintJob_endPrintRawData+0x1D42
Library=E:\j2sdk_nb\j2sdk1.4.2\jre\bin\awt.dll
followed by a list of all dynamic link libraries running.
This log is additionally written to a file.
Here is the code:
import java.awt.*;
import java.awt.image.*;
import javax.swing.JFrame;
public class MonsunScreenManager
     private GraphicsDevice gDevice = null;
     /** change this if you want a different bufferstrategy **/
     private static final int NUM_DISPLAY_BUFFERS = 2;
     private static MonsunScreenManager screenManager = new MonsunScreenManager();
     private MonsunScreenManager()
          GraphicsEnvironment env =
               GraphicsEnvironment.getLocalGraphicsEnvironment();
          gDevice = env.getDefaultScreenDevice();
     public static MonsunScreenManager getScreenManager()
          return screenManager;
     /** get compatible displaymodes of system **/
     public DisplayMode[] getCompatibleDisplayModes()
          return gDevice.getDisplayModes();
     /** get first compatible mode, or null if none are **/
     public DisplayMode getFirstCompatibleMode( DisplayMode modes[] )
          DisplayMode goodModes[] = gDevice.getDisplayModes();
          for(int i=0;i<modes.length;i++)
               for(int j=0;j<goodModes.length;j++)
                    if(displayModesMatch(modes,goodModes[j]))
                         return modes[i];
          return null;
     /** get current display mode **/
     public DisplayMode getCurrentDisplayMode()
          return gDevice.getDisplayMode();
     /* check if 2 display modes match. (same resolution, bit depth, and refresh
     * rate). if refresh rate is unknown, only the other two have to match. if bit
     * depth is multi, only the other two have to match.
     public boolean displayModesMatch( DisplayMode mode1, DisplayMode mode2 )
          if(     mode1.getWidth()      != mode2.getWidth()     ||
               mode1.getHeight()     != mode2.getHeight())
               return false;
          if(     mode1.getBitDepth()     !=     DisplayMode.BIT_DEPTH_MULTI     &&
               mode2.getBitDepth()     !=     DisplayMode.BIT_DEPTH_MULTI     &&
               mode1.getBitDepth()     !=     mode2.getBitDepth())
               return false;
          if(     mode1.getRefreshRate()     !=     DisplayMode.REFRESH_RATE_UNKNOWN     &&
               mode2.getRefreshRate()     !=     DisplayMode.REFRESH_RATE_UNKNOWN     &&
               mode1.getRefreshRate()     !=     mode2.getRefreshRate())
               return false;
          return true;
     /** changes to fullscreen mode. **/
     public void setFullScreen(DisplayMode displayMode)
          JFrame myDisplay = new JFrame();
          myDisplay.setUndecorated(true);
          myDisplay.setIgnoreRepaint(true);
          myDisplay.setResizable(false);
          gDevice.setFullScreenWindow(myDisplay);
          if(displayMode!=null && gDevice.isDisplayChangeSupported())
               try
                    gDevice.setDisplayMode(displayMode);
               catch(IllegalArgumentException e)
                    System.out.println("Boo?");
          myDisplay.createBufferStrategy(NUM_DISPLAY_BUFFERS);
     /** get the graphical context for the display **/
     public Graphics2D getGraphics()
          Window myWindow = gDevice.getFullScreenWindow();
          if(myWindow!=null)
               BufferStrategy bufferStrat = myWindow.getBufferStrategy();
               return (Graphics2D)bufferStrat.getDrawGraphics();
          return null;
     /** updates the display **/
     public void updateScreen()
          Window myWindow = gDevice.getFullScreenWindow();
          if(myWindow!=null)
               BufferStrategy bufferStrat = myWindow.getBufferStrategy();
               if(bufferStrat.contentsLost())
                    bufferStrat.show();
          // sync display! should be an "option", since it takes time??
          Toolkit.getDefaultToolkit().sync();
     /** returns the window used in fullscreen, or null if not in fullscreen! **/
     public Window getFullScreenWindow()
          return gDevice.getFullScreenWindow();
     /** returns width of window, or 0 if not in fullscreen mode **/
     public int getWidth()
          Window myWindow = getFullScreenWindow();
          if(myWindow!=null)
               return myWindow.getWidth();
          return 0;
     /** returns height of window, or 0 if not in fullscreen mode **/
     public int getHeight()
          Window myWindow = getFullScreenWindow();
          if(myWindow!=null)
               return myWindow.getHeight();
          return 0;
     /** restores the screen's display mode **/
     public void restoreScreen()
          Window myWindow = getFullScreenWindow();
          if(myWindow!=null)
               myWindow.dispose();
          gDevice.setFullScreenWindow(null);
     /** creates an image compatible with the current displaymode **/
     public BufferedImage createCompatibleImage(int dWidth,int dHeight, int dTrans)
          Window myWindow = getFullScreenWindow();
          if(myWindow!=null)
               GraphicsConfiguration gC = myWindow.getGraphicsConfiguration();
               return gC.createCompatibleImage(dWidth,dHeight,dTrans);
          return null;