java - BufferedImage 的 getGraphics() 中出现空指针异常？

Question

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){}
}

问题出在哪里？

Answer 1

显然，方法 createImage(int, int) 返回 null。原因在documentation中有解释。 :

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.