What could be causing this socket not to find a port?

Question

I am trying to create a server that receives UDP packets and responds with UDP messages. However, I can't seem to get it to bind to a port. Here's my constructor for the class:

public UDPServer() throws IOException {
    myGUI = new ServerGUI();
    myClientList = new ArrayList<ClientInfo>();
    DatagramChannel channel = DatagramChannel.open();
    mySocket = channel.socket();

    //mySocket = new DatagramSocket(null);      
    //mySocket.setReuseAddress(true);
    //mySocket.bind(new InetSocketAddress("localhost", Constants.SERVER_PORT_NUM));

    myPortNum = mySocket.getPort();
    myIP = mySocket.getInetAddress();
    System.out.println(myPortNum + "   " + myIP.toString());
}

I have tried both the channel method and the commented out method, and I even used this method to try and find an open port:

private DatagramSocket createNewSocket() throws IOException {
    for (int i = Constants.MIN_PORT_NUM; i < Constants.MAX_PORT_NUM; i++){
        try {
            System.out.println(i);
            return new DatagramSocket(i);
        } catch (IOException e){
            continue; // try next port
        }
    }

    throw new IOException("No free port found");
}

But I've had no luck so far. The portNum keeps coming up as -1 and the IP is null. Any ideas what could be going on here?

EDIT: When I run the following in debug mode and scroll over mySocket to see what values it contains, it says that:

bound = true
closed = false
connectedAddress = null
connectedPort = -1

But when I run mySocket.getLocalPort(), it returns a valid port number. What's going on here?

Here's the code:

public UDPServer() throws IOException {
    myGUI = new ServerGUI();
    myClientList = new ArrayList<ClientInfo>();

    mySocket = new DatagramSocket(Constants.SERVER_PORT_NUM);
    mySocket.setReuseAddress(true);

    myPortNum = mySocket.getLocalPort();
    myIP = mySocket.getInetAddress();
    System.out.println(mySocket);
}

Answer 1

You don't need to do this. Just create it with the non-args constructor, or specify port zero. The system will allocate a free port for you.