Java How to Program Fourth Edition - DCC

Chapter 17 Networking 1051
244 // when received, display new messages in messageArea
245 public void messageReceived( String from, String message )
246 {
247 // append message using MessageDisplayer and
248 // invokeLater, ensuring thread-safe access messageArea
249 SwingUtilities.invokeLater(
250 new MessageDisplayer( from, message ) );
251
252 } // end method messageReceived
253
254 } // end MyMessageListener inner class
255
256 // MessageDisplayer displays a new messaage by
257 // appending the message to the messageArea JTextArea. This
258 // Runnable object should be executed only on the Event
259 // thread, because it modifies a live Swing component.
260 private class MessageDisplayer implements Runnable {
261
262 private String fromUser;
263 private String messageBody;
264
265 // MessageDisplayer constructor
266 public MessageDisplayer( String from, String body )
267 {
268 fromUser = from;
269 messageBody = body;
270 }
271
272 // display new message in messageArea
273 public void run()
274 {
275 // append new message
276 messageArea.append( "\n" + fromUser + "> " +
277 messageBody );
278
279 // move caret to end of messageArea to ensure new
280 // message is visible on screen
281 messageArea.setCaretPosition(
282 messageArea.getText().length() );
283 }
284
285 } // end MessageDisplayer inner class
286 }
Fig. Fig. Fig. 17.20 17.20 ClientGUI subclass of JFrame for presenting a GUI for viewing and
sending chat messages (part 6 of 6).
ClientGUI uses a MessageManager (line 41) to handle all communication with
the chat server. Recall that MessageManager is an interface and therefore allows ClientGUI
to use any MessageManager implementation without the need to change any
code in ClientGUI. Class ClientGUI also uses a MessageListener (line 44) to
receive incoming messages from the MessageManager.
The ClientGUI constructor (lines 47–183) takes as an argument the Message-
Manager for communicating with DeitelMessengerServer. Line 52 sets the Cli-