New to Java

I've been having a problem with the getGraphics() method in my code throwing Null Pointer Exceptions, as early on in the code graphics are taken from an image and loaded into a variable, and as there are currently no graphics in the image, getGraphics() returns null. Of course, when I try to run this, Java doesn't like it.

public class myPanel extends JPanel
{
	private Image img;
	private Graphics g1;

	public myPanel() { // all instances must be prepared
		x1 = 300;
		y1 = 300;
		img = createImage(x1, y1); 		
		g1 = img.getGraphics();	
		run();
	}

	public void run() {
		makeGraphics();
	}

	public void paint(Graphics g) {
		update(g); 
	}
	
	public void update(Graphics g) {
		g.drawImage(img, 0, 0, this);
	}
	
	private void makeGraphics() { 
		int x, y;
			
		for (x = 0; x < x1; x++) {
			for (y = 0; y < y1; y++) {
				g1.drawLine(x, y, x + 1, y);			
			}
		}
	}
	
}

This is a completely stripped down version of the code, so don't worry if it looks a bit pointless. I'm just wondering if there is a way to get round this getGraphics() problem? I read an article yesterday which said not to use it at all!

Looking at the code myself, I don't totally understand how the g1 image gets painted, and because I'm converting this from an Applet to a JPanel I'm not entirely sure if the methods run in the correct order.

I understand Applets have init(), start(), stop() and destroy() methods. What would be the JPanel equivalent of these, and when do these methods run?

Thanks for any help you can give.