Once the scanner thread is over a new frame is opened, with the results of
the scan.

Anyway, if I don't call the join() method on the main thread or if I don't
make a while loop until the scanner thread is over the scanning process
stops immediately, often without reporting any result.

The actual code is something like this:

// The main class:
public void actionPerformed(ActionEvent e)  {
 if (e.getActionCommand() == "Scan" )  {
   Thread t = new Scan();
   t.start();

   try  {
     t.join();
   }

   catch (InterruptedException e)  {}

   // Or: while (t.isAlive())  Thread.yield();

// And this is the method run() in the "Scan" class:

public void run()  {
 curPos=0;
 int ports[] = new int[PORT_NUM];

 for (int i=0; i<PORT_NUM; i++)  {
   try  {
     Socket s = new Socket(host_name,i);

     if (!s.isClosed())  {
       ports[curPos]=i;
       curPos++;
     }
   }

   catch (IOException e)  {}
   ........

And then it prints the results of the scan (the open ports now stored in
the array "ports") in a JTable or something like that. But using join() or
yield() causes the main frame to "freeze" until the scanner thread is
over, and I just wanted to know if there's a way to keep it alive while
the scan is in progress...thanks for the help.