PaintChat GUI thread issue using Swing

Question

Hi there, I'm making a paintchat program for fun and have gotten it to work locally but now I would like to add the networking parts in. I have a function like this in a class called Util:
public static NewscastMessage sendMessage(NewscastMessage message, int srcID, IPeerDescriptor dstPeer) {
System.out.println("sending message");
NewscastMessage replyMessage = null;
String errorMessage = null;
try {
Socket socket = new Socket(dstPeer.getAddress(), dstPeer.getPortNumber());
socket.setSoTimeout(5 * 1000); // timeout to 30 seconds
ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
out.writeObject(message);
replyMessage = (NewscastMessage)in.readObject();
out.close();
in.close();
socket.close();
return replyMessage;
} catch (ConnectException ex) {
Logger.getLogger(PeerClient.class.getName()).log(Level.SEVERE, ex.getMessage());
errorMessage = ex.getMessage();
} catch (SocketTimeoutException ex) {
Logger.getLogger(PeerClient.class.getName()).log(Level.SEVERE, ex.getMessage());
errorMessage = ex.getMessage();
} catch (IOException ex) {
Logger.getLogger(PeerClient.class.getName()).log(Level.SEVERE, ex.getMessage());
errorMessage = ex.getMessage();
} catch (ClassNotFoundException ex) {
Logger.getLogger(PeerClient.class.getName()).log(Level.SEVERE, ex.getMessage());
errorMessage = ex.getMessage();
} catch (RuntimeException ex) {
Logger.getLogger(PeerClient.class.getName()).log(Level.SEVERE, ex.getMessage());
errorMessage = ex.getMessage();
return new NewscastError(srcID, "While trying to send a message to the Peer with id [ " +
dstPeer.getId() + " ] that has the ip address " + dstPeer.getAddress() + ". \nException on peer " + srcID + ": " + errorMessage);
Essentially when a user types a message into a text field and presses enter, I catch the event and append the text into a text area locally then afterwards I'd like to send this message to a peer via Util.sendMessage. When it gets to this sending part, this error occurs:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
I thought it might be some issues with the event lock and surrounded the call to sendMessage with a synchronize block and didn't work. Any ideas? Thanks in advance.

Answer 1

Sorry forgot to attach the later part:
private void sendTextToDestination(String text){
// send via socket
synchronized (this) {
IPeerDescriptor dst = _peer.getPartialView().getOwnerPeerDescriptor();
NewscastText message = new NewscastText(_peer.getPortNumber(), text);
NewscastMessage replyMessage = null;
replyMessage = Util.sendMessage((NewscastMessage) message, _peer.getPortNumber(), dst);
private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {                                           
String newline = "\n";
String text = jTextField1.getText();
jTextArea1.append(text + newline);
jTextField1.selectAll(); // after pressing enter, highlight text
//Make sure the new text is visible, even if there
//was a selection in the text area.
jTextArea1.setCaretPosition(jTextArea1.getDocument().getLength());
synchronized(this){
sendTextToDestination(text); -------> this is where the error occurs
}