Re: java.lang.NullPointerException

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import javax.swing.*;

public class ResourceTest
{
   public static void main(String[] args)
   {
      ResourceTestFrame frame = new ResourceTestFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setVisible(true);
   }
}

/**
   Un frame con un pannello che ha componenti che mostrano
   accesso alle risorse da un file JAR.
*/
class ResourceTestFrame extends JFrame
{
   public ResourceTestFrame()
   {
      setTitle("ResourceTest");
      setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
      setContentPane(new AboutPanel());
   }

   public static final int DEFAULT_WIDTH = 300;
   public static final int DEFAULT_HEIGHT = 300;
}

/**
   Un pannello con un'area di testo e un pulsante "About". Premendo
   il pulsante si riempie l'area di testo con un testo da una risorsa.
*/
class AboutPanel extends JPanel
{
   public AboutPanel()
   {
      setLayout(new BorderLayout());

      // aggiunge area di testo
      textArea = new JTextArea();
      add(new JScrollPane(textArea), BorderLayout.CENTER);

      // aggiunge pulsante About
      URL aboutURL = AboutPanel.class.getResource("about.gif");
      
      System.out.println(aboutURL);
      
      
      JButton aboutButton = new JButton("About",
         new ImageIcon(aboutURL));
      aboutButton.addActionListener(new AboutAction());
      add(aboutButton, BorderLayout.SOUTH);
   }

   private JTextArea textArea;

   private class AboutAction implements ActionListener
   {
      public void actionPerformed(ActionEvent event)
      {
         try
         {
            // legge testo da risorse nell'area di testo
            InputStream in = AboutPanel.class.
               getResourceAsStream("about.txt");
            BufferedReader reader = new BufferedReader(new
               InputStreamReader(in));
            String line;
            while ((line = reader.readLine()) != null)
               textArea.append(line + "\n");
         }
         catch(IOException exception)
         {
            exception.printStackTrace();
         }
      }
   }
}