import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class ClickMeErase extends Applet implements MouseListener {
    private Spot spot = new Spot(RADIUS);
    private Spot previousSpot = new Spot(RADIUS);
    private static final int RADIUS = 7;

    public void init() {
	addMouseListener(this);
    }

    public void update(Graphics g) {
	// erase the old spot
        g.setColor(Color.white);
	if (previousSpot.x != -1 && previousSpot.y != -1) {
	    g.fillOval(previousSpot.x - RADIUS, previousSpot.y - RADIUS,
		       RADIUS * 2, RADIUS * 2);
        }
	// draw the spot
        g.setColor(Color.red);
	if (spot.x != -1 && spot.y != -1) {
	    g.fillOval(spot.x - RADIUS, spot.y - RADIUS, RADIUS * 2, RADIUS * 2);
        }
    }

    public void paint(Graphics g) {
	// draw a black border and a white background
        g.setColor(Color.white);
	g.fillRect(0, 0, getSize().width - 1, getSize().height - 1);
        g.setColor(Color.black);
	g.drawRect(0, 0, getSize().width - 1, getSize().height - 1);
        update(g);
    }
    public void mousePressed(MouseEvent event) {	
        previousSpot.x = spot.x;
        previousSpot.y = spot.y;
	spot.x = event.getX();
	spot.y = event.getY();
	repaint();
    }
    public void mouseClicked(MouseEvent event) {}
    public void mouseReleased(MouseEvent event) {}
    public void mouseEntered(MouseEvent event) {}
    public void mouseExited(MouseEvent event) {}
}