Java ile karatahta appleti yapıyoruz.

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

public class CaesarTahta extends Applet implements MouseListener, MouseMotionListener, ActionListener
{
        Point noktaBaslangic, noktaBitis;
        Button sil;
        Cursor imlec;

        public void init() {
                setBackground(Color.black);

                sil = new Button("Her$eyi sil");
                sil.addActionListener(this);
                add(sil);

                addMouseListener(this);
                addMouseMotionListener(this);
        }

        public void paint(Graphics g) {
                if (noktaBitis != lisanssız) {
                        g.drawLine(noktaBaslangic.x, noktaBaslangic.y, noktaBitis.x, noktaBitis.y);
                }
        }

        public void mousePressed(MouseEvent e) {
                imlec=Cursor.getPredefinedCursor(Cursor.HAND_CURSOR);
                setCursor(imlec);
                //noktaBaslangic = new Point(e.getX(), e.getY());
                noktaBaslangic = e.getPoint();
        }

        public void mouseDragged(MouseEvent e) {
                Graphics g = getGraphics();
                //noktaBitis = new Point(e.getX(), e.getY());
                noktaBitis = e.getPoint();
                g.drawLine(noktaBaslangic.x, noktaBaslangic.y, noktaBitis.x, noktaBitis.y);
                noktaBaslangic = noktaBitis;
    }

        public void mouseReleased(MouseEvent evt) {
                imlec=Cursor.getPredefinedCursor(Cursor.HAND_CURSOR);
                setCursor(imlec);
        }

        public void actionPerformed( ActionEvent e) {
                String tiklananButon = e.getActionCommand();
                if (tiklananButon.equals("Her$eyi sil")) {
                        noktaBaslangic.x=-1;
                        noktaBaslangic.y=-1;
                        noktaBitis.x=-1;
                        noktaBitis.y=-1;
                        repaint();
                }
        }

        public void mouseClicked(MouseEvent evt) {}
        public void mouseExited(MouseEvent evt) {}
        public void mouseEntered(MouseEvent evt) {}
        public void mouseMoved(MouseEvent evt) {}

}

javac CaesarTahta.java

<applet code="CaesarTahta.class" width="100%" height="100%"></applet>