Question

What would this statement do:

ServerSocket ss=new ServerSocket(4646);

Please explain in layman terms.

Answer 1

The statement effectively tells the JVM to listen on port specified (4646) for incoming connections. By itself it doesn’t mean anything since you will have to take incoming connections to that port and use them to build normal Socket objects that will be then used for ingoing/outgoing data.

You could say that the ServerSocket is the object through which real TCP sockets between clients and the server are created. When you create it, the JVM hooks to the operating system telling it to dispatch connections that arrive on that port to your program.

What you typically do is something like:

public AcceptThread extends Thread {
  public void run() {
    ServerSocket ss = new ServerSocket(4646);
    while (true) {
      Socket newConnection = ss.accept();
      ClientThread thread = new ClientThread(newConnection);
      thread.start();
    }
  }
}

So that you will accept incoming connections and open a thread for them.