import java.awt.*;
import java.awt.event.*;

public class Mauskugel extends Frame {

    MousePositionTracker mt = new MousePositionTracker();
    int x=50,y=50;


    public Mauskugel() {
        this.setSize(500,500);
        this.setVisible(true);
        addMouseMotionListener(mt);

        this.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e)
            {System.exit(0);}
        });

        while (true) {
            if ((mt.getX()>50)&&(mt.getX()<150)&&(mt.getY()>50)&&(mt.getY()<150)) {
                run();
            }
        }
    }

    public void run() {
        while (true) {
            x=mt.getX()-12;
            y=mt.getY()-12;
            repaint();

            try {
                Thread.sleep(0,1);
            } catch (Exception e) {};
        }

    }

    public void paint (Graphics g) {
        g.setColor(Color.blue);
        g.fillOval(x,y,100,100);
    }

}