Updating GUI

Question

Hello Techies,
How can i update my gui.
My gui is having 2 combo boxes , one text field and one button. when i click on button the request must go to the TCP server and receive the responses from TCPServer.
My problem is that when i first click on Button,the request is going to the TCP and getting reply.
I will get continuous responses from TCP server.
I am getting first response from the server.
Second response I am getting the following error.
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
     at javax.swing.JComponent.getComponentGraphics(Unknown Source)
     at javax.swing.JComponent.paint(Unknown Source)
     at javax.swing.JComponent.update(Unknown Source)
     at testForSwing1$4.run(testForSwing1.java:475)
     at java.awt.event.InvocationEvent.dispatch(Unknown Source)
     at java.awt.EventQueue.dispatchEvent(Unknown Source)
     at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)
     at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
     at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
     at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
     at java.awt.EventDispatchThread.run(Unknown Source)Here is my Code
import java.awt.Component;
import java.awt.Container;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GraphicsConfigTemplate;
import java.awt.GraphicsConfiguration;
import java.awt.Image;
import java.awt.Label;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.lang.reflect.InvocationTargetException;
import java.net.Socket;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;
import javax.swing.plaf.ComponentUI;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
public class testForSwing1 extends JPanel implements ActionListener {
    public static Socket socket ;
       JTextField textField;
       JComboBox exchangeComboBox;
       JComboBox fieldsComboBox;
       JButton button;
        public testForSwing1(List List, List )
     super();
     // TODO Auto-generated constructor stub
     JLabel exchLabel = new JLabel("xxxName");
     xxxComboBox = new JComboBox(List.toArray());
     add(xxxLabel);
     add(xxxComboBox);
                      xxxComboBox.addActionListener(this);
     out = outStream;
     in = inStream;
     JLabel fieldLabel = new JLabel("yyy");
     fieldsComboBox = new JComboBox(fieldsList.toArray());
     add(fieldLabel);
     add(fieldsComboBox);
     fieldsComboBox.addActionListener(this);
     textField = new JTextField(15);
     add(textField);
     button = new JButton("clickMe");
     button.addActionListener(this);
     add(button);
     public void actionPerformed(final ActionEvent ae)
     final  JButton ts = (JButton)ae.getSource();
     if ((ae.getActionCommand().equalsIgnoreCase("clickMe"))) {
     //try
     Runnable tcpConnection = new Runnable()
     public void run()
              try
                    out = new DataOutputStream(socket.getOutputStream());
                      in = new DataInputStream(socket.getInputStream());
                                                                                      out.writeBytes(ram);                               
              out.writeByte('\n');
                                                                 while(socket.getInputStream()!= null)
         System.out.println("echo: " + in.readLine());
         update( grap );
catch (IOException ioe) {
                     System.out.println("IOException"+ioe.getMessage());
                                             SwingUtilities.invokeLater(tcpConnection);
                              break outt;
      * @param args
     public static void main(String[] args) {
          // TODO Auto-generated method stub
          //List list1InMainMethod = new ArrayList();
          //List list2InMainMethod = new ArrayList();
              try {
               File sourceXmlFile = new File(args[0]);
               File fidsXmlFile = new File(args[1]);
               DocumentBuilderFactory dbFactory = DocumentBuilderFactory
                         .newInstance();
                socket = new Socket("test",90);
     createAndShowGUI(xxxFile, yyyFile);
          } catch (ParserConfigurationException pce) {
               // TODO: handle exception
               System.out.println("ParserConfiguration exception"
                         + pce.getMessage());
          } catch (SAXException saxe) {
               // TODO: handle exception
               System.out.println("SAXException" + saxe.getMessage());
          } catch (IOException ioe) {
               // TODO: handle exception
               System.out.println("IOExceptionxxxx" + ioe.getMessage());
public static Graphics grap;
     public static void createAndShowGUI(List list1InCreateAndShowGUI,
               List list2InCreateAndShowGUI,DataOutputStream out,DataInputStream in) {
          // Make sure we have nice window decorations.
          //try
          JFrame.setDefaultLookAndFeelDecorated(true);
          // Create and set up the window.
          JFrame frame = new JFrame("ComboBoxDemo");
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     JComponent newContentPane = new testForSwing1(list1InCreateAndShowGUI,
                    list2InCreateAndShowGUI,out,in);
          newContentPane.setOpaque(true); // content panes must be opaque
          //grap = newContentPane.getGraphics();
          frame.setContentPane(newContentPane);
          // Display the window.
          frame.pack();
          frame.setVisible(true);
}I had posted only GUI coding only..
SwingUtilities.invokeLater(new Runnable()
                   public void run()
                                    try
                                          out = new DataOutputStream(socket.getOutputStream());
                                          in = new DataInputStream(socket.getInputStream());
                                          //Change
                                         out.writeBytes(s);                               
                                          out.writeByte('\n');
                                          //change over
                                        while(socket.getInputStream()!= null)
                                       System.out.println("echo: " + in.readLine());
                                       Object c = in.readLine();
                                       update(grap);
                                    catch (IOException ioe) {
                                             // TODO: handle exception
                                         System.out.println("IOException"+ioe.getMessage());
          I am getting nullpointer exception in update(grap);
If i dont use this update(grap) my gui is going to block.
How can i solve this problem. Plz guide me. I had stucked here very long time back.
Thanks(Inadvance),
ramu.

Answer 1

Hello camie,
The above problem is working fine when i create thread for each request.
when i use nio,instead of threading, the gui is not responding i.e going to be stucked.
I am using nio , since the response from the Server which is appearing in the console is sometimes is machine code, some times some of the characters in the response is missing.
Here is my code.
public class JabberClient1
      testForSwing1 tfs1 = new testForSwing1();
      public void connect(String s,testForSwing1 tfs,SocketChannel  scc,Selector see)throws IOException
           SocketChannel sc = scc;
           Selector sel = see;
          String str = s;
           tfs1=tfs;
          try 
                  int i = 0;
      // Because of the asynchronous nature you do not know
      // when reading and writing is done, hence you need to
      // keep track of this, boolean written is used to
      // alternate between read and write. Whatever is written
      // is echoed and should be read.
      // boolean done is used to check when to break out of
      // the loop
      boolean written = false, done = false;
      String encoding = System.getProperty("file.encoding");
      Charset cs = Charset.forName(encoding);
      ByteBuffer buf = ByteBuffer.allocate(1024);
        while(!done) {
        sel.select();
        Iterator it = sel.selectedKeys().iterator();
          while(it.hasNext()) {
          SelectionKey key = (SelectionKey)it.next();
          it.remove();
          tfs1.repaint();
          sc = (SocketChannel)key.channel();
          if(key.isConnectable() && !sc.isConnected()) {
               System.out.println("is connected");
            InetAddress addr = InetAddress.getByName(null);
          if(key.isReadable() ) {
            if(sc.read((ByteBuffer)buf.clear()) > 0) {
                                  System.out.println("is reading()");
                 String response = cs.decode(
                (ByteBuffer) buf.flip()).toString();
              System.out.print(response);
              if(response.indexOf("END") != -1)
              done = true;
              tfs1.repaint();
          if(key.isWritable() &&!written ) {
               System.out.println("is writting");
             System.out.println("string length"+s.length()); 
            if(i < s.length())
                 sc.write(ByteBuffer.wrap(new String(s+ '\n').getBytes()));
            else if(i == s.length())
                 sc.write(ByteBuffer.wrap(new String("END\n").getBytes()));
            written = true;
          tfs1.repaint();
            i++;
    } finally {
      sc.close();
      sel.close();
  in my testForSwing1.java program
  public static void main(String[] args)
            sc = SocketChannel.open();
            sel = Selector.open();
            sc.connect(new InetSocketAddress("localhost", 7890));
            sc.configureBlocking(false);
            sc.register(sel, SelectionKey.OP_READ |
                                   SelectionKey.OP_WRITE  |  SelectionKey.OP_CONNECT);
JabberClient1 jc= new JabberClient1();
System.out.println("sxxxxxxx"+s);
try
     jc.connect(s,tfs,sc,sel);
catch (IOException e)
     System.out.println("ioexception"+e.getMessage());
              Second code which i had placed is not complete.
my gui is not respondin when the i want to second request.
plz guide me.....
regards,
ramu.