import java.awt.*;

public class ConcentricCircles {

	public static Color getRandomColor() {
		int r = (int)(Math.random() * 256);
		int g = (int)(Math.random() * 256);
		int b = (int)(Math.random() * 256);
		return new Color(r,g,b);
	}

	public static void concentricCircles(
		Graphics2D g, int nCircles, int width, int height)
		throws InterruptedException {
		int left = 0;
		int top = 0;
		int w = width;
		int h = height;
		int wAdjust = width/nCircles;
		int hAdjust = height/nCircles;
		// top-left offsets are 1/2 the circle size adjustment
		int leftAdjust = width/(nCircles*2);
		int topAdjust = height/(nCircles*2);
		for (int n = 0; n < nCircles; n++) {
			g.setColor(Color.BLACK);
			g.drawRect(left, top, w, h);
			g.setColor(getRandomColor());
			g.fillOval(left, top, w, h);
			Thread.sleep(1000);
			// Comment out each of the 4 lines below one-at-a-time
			// to see what each of them does.
			left += leftAdjust;
			top += topAdjust;
			w -= wAdjust;
			h -= hAdjust;
		}
	}

	public static void main(String[] args)
		throws InterruptedException {
		DrawingPanel dp = new DrawingPanel(400, 600);
		dp.setBackground(Color.WHITE);
		Graphics2D g = dp.getGraphics();
		concentricCircles(g, 10, dp.getWidth(), dp.getHeight());
	}

}