Null Pointer Exception in getGraphics() for BufferedImage?

开发者_Go百科public void saveImage(String path){
    BufferedImage image = (BufferedImage) createImage(500, 500);
    Graphics gImage = image.getGraphics(); //<<<<<<<<--- exception
    paint(gImage);
    image = image.getSubimage(0,0,500,500);     
    try {
        ImageIO.write(image, "png", new File(path+".png"));
    }
    catch (Exception e){}
}

Where is the problem ??

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Apparently the method createImage(int, int) is returning null. The reason is explained in the documentation:

Returns:
an off-screen drawable image, which can be used for double buffering. The return value may be null if the component is not displayable. This will always happen if GraphicsEnvironment.isHeadless() returns true.

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Your NPE is probably not coming from getGraphics but from trying to dereference a null image variable. If your component is not displayable, createImage returns null.