Java Swing - 如何扩展以创建JLabel，以显示具有下划线文本的URL标签，并且可点击

//The contents of this file are subject to the Mozilla Public License Version 1.1
//(the "License"); you may not use this file except in compliance with the 
//License. You may obtain a copy of the License at http://www.mozilla.org/MPL/
//
//Software distributed under the License is distributed on an "AS IS" basis,
//WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License 
//for the specific language governing rights and
//limitations under the License.
//
//The Original Code is "The Columba Project"
//
//The Initial Developers of the Original Code are Frederik Dietz and Timo Stich.
//Portions created by Frederik Dietz and Timo Stich are Copyright (C) 2003. 
//
//All Rights Reserved.

import java.awt.Color;
import java.awt.Cursor;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.event.MouseEvent;
import java.net.URL;

import javax.swing.JLabel;
import javax.swing.JOptionPane;

public class Main {
  public static void main(String[] args) throws Exception {
    URLLabel label = new URLLabel(new URL("http://w3cschool.cn"));

    JOptionPane.showMessageDialog(null, label);

  }
}
 class URLLabel extends JLabel {

  boolean entered = false;

  boolean mousehover;

  public URLLabel(URL url) {
    this(url, url.toString());
  }

  public URLLabel(URL url, String str) {
    super(str);

    setForeground(Color.blue);
    mousehover = false;

  }

  public void mouseEntered(MouseEvent e) {
    setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
    entered = true;

    if (mousehover) {
      repaint();
    }
  }

  public void mouseExited(MouseEvent e) {
    setCursor(Cursor.getDefaultCursor());
    entered = false;

    if (mousehover) {
      repaint();
    }
  }

  public void mousePressed(MouseEvent e) {
  }

  public void mouseReleased(MouseEvent e) {
  }

  public void paint(Graphics g) {
    super.paint(g);

    if (entered || !mousehover) {
      Rectangle r = g.getClipBounds();

      g.drawLine(0, r.height - this.getFontMetrics(this.getFont()).getDescent(), this
          .getFontMetrics(this.getFont()).stringWidth(this.getText()), r.height
          - this.getFontMetrics(this.getFont()).getDescent());
    }
  }
}