怎么在java里画出小圆点

怎么在java里画出小圆点

package test;

import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Toolkit;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class PaintDemo extends JFrame{


private static final long serialVersionUID = -95348909224392777L;
JPanel c=canvas();
public PaintDemo(){
this.setTitle("Small point paint test");
int w=300,h=300;
this.setSize(w, h);
Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
this.setSize(w,h);
this.setLocation(screenSize.width / 2 - w / 2,
screenSize.height / 2 - h / 2);
this.setLayout(null);

this.add(this.c);
this.c.setBounds(0, 0, 300, 300);
this.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
dispose();
System.exit(0);
}
});

this.setVisible(true);
}
public JPanel canvas() {
JPanel panel = new JPanel() {
private static final long serialVersionUID = 1L;

@Override
public void paint(Graphics g) {
super.paint(g);
g.fillOval(100, 100, 100, 100);
}
};
return panel;
}


public static void main(String[] args) {
new PaintDemo();
}

}