Mouse Event in Applet in Java

import java.awt.*;
import java.applet.*;
import java.awt.event.*;
//<applet code="circle.class" width=200 height=300></applet>
public class circle extends Applet
{
int x,y;
public void init()
{
 add a=new add();
 addMouseListener(a);
}
 public void paint(Graphics g)
{
g.fillOval(x,y,30,30);
}
class add implements MouseListener
{
public void mouseClicked(MouseEvent e)
{
}
public void mouseEntered(MouseEvent e)
{
x=e.getX();
y=e.getY();
repaint();
}
public void mouseReleased(MouseEvent e){}
public void mousePressed(MouseEvent e){}
public void mouseExited(MouseEvent e){

}
}
}