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Message:

Creating an image using java

Posted by Ramu on November 02, 2001 at 8:55 AM

>
> I've been trying to get rid of NullPointerEx. here for about 2 days!
> First it came up at createImage() which was returning Null.
> Adding a call to show() solved that one but, there is now
> a NullPointerEx. at drawImage(). I got it working once! This code
> seems to work fine under Windows, but not Solaris.

> Cheers,
> Adam.

>
> public void draw(Graphics g)
> { //set screen colours
> Color bg = Color.white;
> Color fg = Color.blue;
> Color cartColor = new Color(0,20,255);
> Color poleColor = new Color(100,100,0);
> Color arrowColor = new Color(255,255,0);
> Color trackColor = new Color(100,100,50);

> //get window size
> Dimension d = size();
> //System.out.println( d );

> // actual screen position of cart
> int posx=(int)(d.width/2-sim.x*pixelspermeter);
> int posy=(d.height/2-cartheight);
>
> //Create the offscreen graphics context, if no good one exists.
> if((offGraphics==null)
> || (d.width!=offDimension.width)
> || (d.height!=offDimension.height) ) {

> show(); // needed to stop NullPointerEx. from createImage
> offDimension = d;

> offImage = createImage(d.width, d.height); // returning null ??

> if( offImage == null ) System.out.println( "offImage == null" );
> //System.out.println(offImage);
> System.out.println( "\n*** 1 ***" );
> offGraphics = offImage.getGraphics();
> if( offGraphics == null ) System.out.println( "offGraphics == null" );
> System.out.println( "*** 2 ***" );
> }

> //Erase the previous image.
> offGraphics.clearRect(0, 0, d.width, d.height);

> //... drawing to offGraphics ...
>
> //Last thing: Paint the image onto the screen.
> System.out.println( "------------>" );
> boolean b = g.drawImage(offImage, 0, 0, this);
> System.out.println( "drawImage = "+b );
> }//draw