Disegno di un cerchio

import java.awt.event.*;
import java .awt.*;
import javax.swing.*;
public class TestaCerchio {
public static void main(String Args[]){
Cerchio c1=new Cerchio();
JFrame f1=new JFrame("Cerchio");
f1.setSize(500,500);
f1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f1.add(BorderLayout.CENTER,c1);
f1.setVisible(true);
}
}

import java.awt.event.*;
import java .awt.*;
import javax.swing.*;
public class Cerchio extends JPanel implements MouseListener {
private int x1;
private int y1;
private int x2;
private int y2;
private double raggio=0;
private int raggioCast=0;
private int conta=0;
public Cerchio(){
addMouseListener(this);
}
@Override public void mouseClicked(MouseEvent e){

}
@Override public void mouseEntered(MouseEvent e){

}
@Override public void mouseExited(MouseEvent e){

}
@Override public void mousePressed(MouseEvent e){
int x=e.getX();
int y=e.getY();
conta++;
if(conta==1){
x1=x;
y1=y;
}
if(conta==2){
x2=x;
y2=y;
double differenza1=x1-x2;
double differenza2=y1-y2;
raggio=Math.sqrt(Math.pow(differenza1,2)+(differenza2));
System.out.println(raggio);
raggioCast=(int)raggio;
System.out.println(raggioCast);
conta=0;
repaint();
}
}
@Override public void mouseReleased(MouseEvent e){

}
@Override public void paintComponent(Graphics g){
g.setColor(Color.BLUE);
g.drawOval(x1, y1, raggioCast, raggioCast);
}
}