Java thread overlap

Question

I'm having some trouble having more than 1 thread in the code. I get the error:

java.net.BindException: Address already in use: JVM_Bind
Exception in thread "Thread-0" java.lang.NullPointerException

Here is my code:

   public static void main( String args[] )
    {

    Thread t1 = new Thread(new server(1));
   t1.start();  

  Thread t2 = new Thread(new server(2));
   t2.start();  
   }

When the thread t2 code is commented out then it works fine.

Not too sure why I get that error, it doesn't make sense to me. Any help would be appreciated.

Answer 1

You have to change your port for the second ServerSocket instance, since only one ServerSocket can be bound to the same port at the same time.

I suggest to improve your server class with something like this:

public class server {
  private static int port = 5000;

  public server(int yourParameter) {
    /*...*/
    service = new ServerSocket(port++);
    /*...*/
  }
}

This code will allow your servers to be bound to an always increasing port, starting from 5000.