Passing a variable from one thread to another

Question

Hi. I'm trying to produce a chat program in Java but need to pass a variable between two threads. I have included a snipet of the code.
import java.io.*;
import java.net.*;
class IndividualConnection extends Thread
     public Socket clientSocket;
     String userName = "";
     public IndividualConnection(Socket connectingSocket)
          clientSocket = connectingSocket;
public login(String name)
userName = name;
     public void messageUser(Socket socket, String msg)
          try
               Socket newSocket = new Socket("192.168.0.162",5163);     
               DataOutputStream outToServer = new DataOutputStream(socket.getOutputStream());
               outToServer.writeBytes(msg + '\n');     
          catch(Exception e)
               System.out.println("The connection with the client has been closed.");
               this.stop();
public void run()
     Socket global = clientSocket;
// etc etc
A number of threads are created based on code similar to the above. Each thread communicates to a different client on the chat program. However, I want to be able to send messages between the clients.
Each thread has a method called messageUser(Socket socket, String msg). I should (hopefully) be able to send a message to anyone using the prog if I can access their socket. The problem is that the socket objects for each client is held in the clients own thread. I have tried writing some code to find the Socket object in another thread but to no success. The code I am trying is shown below.
     public Socket findContact(String name)
          ThreadGroup currentGroup = Thread.currentThread().getThreadGroup();
          int numThreads = currentGroup.activeCount();
          Thread[] listOfThreads = new Thread[numThreads];
          currentGroup.enumerate(listOfThreads);
          for (int i = 0; i < numThreads; i++)
               String threadName = listOfThreads.getName();
               if (threadName.compareTo(name) == 0)
               //     Socket tempSocket = threadName[i].getClass().getField(clientSocket);
          return tempSocket;
The line I have commented out does not work. Please could someone tell me how to carry out this task. I have spent many hours trying to solve this but am not able to. The chat server is nearly complete now. I just need to find a way of obtaining another threads socket.
I hope the problem is comprehensible. I have found it difficult to explain clearly. Many thanks.

Answer 1

Really simple, inelegant solution:
class MyThread extends Thread {
Socket socket;
MyThread( Socket s ) { socket = s; }
public Socket getSocket() { return socket; }
}Better: create a master object that includes an array
of sockets. Each time you create a Thread, update the
master object's list of sockets with a reference to
each Thread's socket. Under the current memory model, the socket field should be declared volatile. The proposed new memory model will guarantee that this will work if the socket field is declared final.
Sylvia.