Simple Chat Client

package chat;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;

/**
* Here's a chat client (meant for two way or group chatting).
* It has two threads so it can simultaneously read
* what the server sends it, and can write and send to the server.
* Not included is the server code, which handles another client or group of clients.
* The server receives everything sent by the clients, and then sends it to every client
* to be written (which is why you see what you just said).
* It's very simple, and sort of the base of text communication over a server.
* It employs the java.net.Socket class, which uses the TCP protocol (meaning that 100% of
* packets are received in the order in which they were sent).
* @author amiller
*
*/
public class ChatClient {
 //address and port information for all users
 private static final int PORT = 1445;
 private static final String SERVER_ADDRESS = "chatAddress";

 private Socket socket;
 private String userName;
 private boolean isConnected;

 public ChatClient(String usrName) throws UnknownHostException, IOException{
     //string to identify user
     userName = usrName;
     //establish the connection and start the threads
     establishConnection();
 }

 public void establishConnection() throws UnknownHostException, IOException{
     //establishes communication with the server
     socket = new Socket(SERVER_ADDRESS, PORT);
     isConnected = true;
 
     Writer writeThread = new Writer();
     Reader readThread = new Reader();
 
     //this starts the reading and the writing.
     writeThread.start();
     readThread.start();
 }

 /**
  * To break from the while loops and kill the
  * reader and writer threads
  */
 public void disconnect(){
     isConnected = false;
 }

 private class Reader extends Thread {
     //reads from the socket connection
     private BufferedReader reader;
     public Reader() throws IOException{
         reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
     }
     public void run(){
         String lineFromServer;
         while(isConnected){
             lineFromServer = null;
             try {
                 lineFromServer = reader.readLine();
             } catch (IOException e) {
                 e.printStackTrace();
             }
             if(lineFromServer != null)
                 System.out.println(lineFromServer);
         }
     }
 
 }
 private class Writer extends Thread {
     //writes to socket
     private PrintWriter writer;
     //listens to the local computer's keyboard
     private BufferedReader reader;

     public Writer() throws IOException{
         writer = new PrintWriter(socket.getOutputStream(), true);
         reader = new BufferedReader(new InputStreamReader(System.in));
     }
     /**
      * This thread is constantly listening for the user's input (locally)
      * When the user has entered a line, it writes it to the socket
      * that has established a connection
      */    
     public void run(){
         while(isConnected){
             try {
                 String line = reader.readLine();
                 if(line != null)
                     writer.println(userName + ": " + line);
             } catch(Exception e){
                 e.printStackTrace();
             }
         }
     }
 }

}