简单画图的请教

jyc8778

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
import java.awt.geom.*;
public class line
{
public static void main(String[] args)
{
CreatFrame frame=new CreatFrame();
frame.setDefaultCloseOperation(3);
frame.setVisible(true);
frame.setResizable(false);
}
}
class CreatFrame extends JFrame
{
public CreatFrame()
{
setTitle("测试");
setSize(X,Y);

CreatPanel panel=new CreatPanel();
Container contentPane=getContentPane();
contentPane.add(panel);
}
public static final int X=320;
public static final int Y=240;
}
class CreatPanel extends JPanel  
{
public double sX;
public double sY;
public double Ex;
public double Ey;
public CreatPanel()
{
addMouseListener(new MouseAdapter()
{
public void mousePressed(MouseEvent e)
{
sX=e.getX();
sY=e.getY();
//System.out.println(sX+":"+sY);
}
public void mouseReleased(MouseEvent e)
{
Ex=e.getX();
Ey=e.getY();
//System.out.println(Ex+":"+Ey);
}
});
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2=(Graphics2D)g;
g2.setColor(Color.RED);
Line2D line=new Line2D.Double(sX,sY,Ex,Ey);
System.out.println(sX+":"+sY);
g2.draw(line);
}
}

编译没错误，为什么运行时候画不出来呢？