My listing program can't execute normally, Please HELP me

Question

Hello,
I am in trouble, this is my listing program:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.text.*;
import javax.swing.event.*;
import javax.swing.border.*;
class Server extends JFrame implements DocumentListener, ActionListener
     private JPanel panel1;
private JPanel panel2;
private JTextField field1;
private JTextField field2;
private JTextField field3;
private JLabel label1;
private JLabel label2;
private JLabel label3;
     private JButton button1;
private JButton button2;
private JOptionPane pane1;
     public Server()
          super("Server");
          setTitle( "Port" );
          setSize( 640, 480 );
          setBackground( Color.gray );
          JPanel topPanel     = new JPanel();
          topPanel.setLayout(new GridLayout(2,2));     
          getContentPane().add( topPanel );
          panel1.setLayout(null);
          panel2.setLayout(null);
          /* --- Panel Message Server --- */
          // Components
          JTextField field1 = new JTextField();
          field1.setBounds(150,40,100,25);
          field1.setFocusAccelerator('a');
          panel1.add(field1);
          JLabel label1 = new JLabel("Port Number:");
          label1.setBounds(60, 40, 260, 20);
          label1.setLabelFor(field1);
          label1.setDisplayedMnemonic('A');
          panel1.add(label1);
          Border etched;
          etched = BorderFactory.createEtchedBorder();
     TitledBorder title;
     title = BorderFactory.createTitledBorder(etched, "Message Server");
title.setTitleJustification(TitledBorder.LEFT);
panel1.setBorder(title);
topPanel.add(panel1);
          /* --- Panel Radius Server --- */
          // Components
          JTextField field2 = new JTextField();
field2.setBounds(170, 40, 100, 25);
field2.setFocusAccelerator('b');
          panel2.add(field2);
          JLabel label2 = new JLabel("Authorized Port:");
          label2.setBounds(60, 40, 260, 20);
          label2.setLabelFor(field2);
          label2.setDisplayedMnemonic('B');
          panel2.add(label2);
          JTextField field3 = new JTextField(10);
          field3.setBounds(170, 80, 100, 25);
          field3.setFocusAccelerator('c');                         
panel2.add(field3);
          JLabel label3 = new JLabel("Account Port:");
          label3.setBounds(60, 80, 260, 20);     
          label3.setLabelFor(field3);
          label3.setDisplayedMnemonic('C');
          panel2.add(label3);
Border etched2;
          etched2 = BorderFactory.createEtchedBorder();
     TitledBorder title2;
     title2 = BorderFactory.createTitledBorder(etched2, "Radius Server");
title2.setTitleJustification(TitledBorder.LEFT);
panel2.setBorder(title2);
topPanel.add(panel2);
          /* --- Button components --- */
          JPanel leftcolumn3 = new JPanel();
          leftcolumn3.add(button1);
          button1.setEnabled(false);
          JPanel rightcolumn3 = new JPanel();
          rightcolumn3.add(button2);
          JPanel ButtonPanel = new JPanel();
          //ButtonPanel.setLayout(new BorderLayout());
          ButtonPanel.add(button1);
          ButtonPanel.add(button2);
          topPanel.add(ButtonPanel);
     // Add a document listener to the first field
          Document document =     field1.getDocument();
          document.addDocumentListener( this );
     // Handle keyboard accelerators
     public void     actionPerformed( ActionEvent e )
          // Get the source of the action event
          JLabel label = (JLabel)e.getSource();
          // Give the associated component the focus
          Component fieldComponent = label.getLabelFor();
          fieldComponent.requestFocus();
     // Handle insertions into the text field
     public void     insertUpdate( DocumentEvent event )
          String     sString     = field1.getText();
          try     
               int     iValue = Integer.parseInt( sString );
               button1.setEnabled( true );
          catch( NumberFormatException e )
               JOptionPane.showMessageDialog(pane1,
"Invalid password. Try again.",
"Error Message",
JOptionPane.ERROR_MESSAGE);
     // Handle deletions     from the text field
     public void removeUpdate( DocumentEvent event )
          // Prevent the user     from entering a blank field
          if(     field1.getText().length() == 0 )
               button1.setEnabled( false );
          else
               // Do the same error checking as insertUpdate()
               insertUpdate( event );
     // Handle changes to the text field
     public void changedUpdate( DocumentEvent event )
          // Nothing to do here
     public static void main( String args[] )
          // Create an instance of the test application
          Server window     = new Server();
          window.setVisible( true );
If I execute this file will appear command like:
" Exception in thread "main" java.lang.NullPointerException
at server.<init><server.java:39>
at server.main<server.java:188> "
Would you help me? please get out me from this problem.
thank's

Answer 1

If I execute this file will appear command like:
" Exception in thread "main"
java.lang.NullPointerException
at server.<init><server.java:39></server>
at server.main<server.java:188></server> "The first thing you need to do is take a look at line 39 in server.java. This is where you are getting your NullPointerException. At a guess I'd say its the following line
panel1.setLayout(null);You don't appear to be assigning any value to panel1 before trying to call a method on it.
Col