Swing的一个问题

[queen_et]

按照下边这段代码，屏幕上应该显示出一个窗口，里面有HelloJava的字样。但实际运行时只显示以窗口，没有HelloJava的字样，问题在哪？
import java.awt.Graphics;

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import java.awt.Color;

/*
* Created on 2004-4-23
*
* TODO To change the template for this generated file go to
* Window - Preferences - Java - Code Generation - Code and Comments
*/
/**
* @author Administrator
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Generation - Code and Comments
*/
public class HelloJava extends JComponent {
public static void main(String[] args) {
JFrame f = new JFrame("HelloJava ");
f.setSize(300,500);
f.getContentPane().add(new HelloJava());
f.setVisible(true);
JOptionPane.showMessageDialog(null,"Hello Java");
}
/* (non-Javadoc)
* @see javax.swing.JComponent#printComponent(java.awt.Graphics)
*/
protected void printComponent(Graphics g) {
// TODO Auto-generated method stub
g.drawString("Hello Java!",125,125);
g.setColor(new Color(102,203,232));
}
}

[wolfsquare]

printComponent - > paintComponent

[rainboy20024]

printComponent - > paintComponent

super.paintComponent(g);