java - null DatagramSocket in RTS server puzzling me


I am back to my RTS in Java. I was persuaded against using Python. I am doing initial client-server connections in TCP Sockets for reliability. Once a client notifies the server in TCP, a serverClient class is instantiated on the server to mange the communication between that client and the server. I have incorporated your advice as much as possible.

It is intended for each serverClient to communicate with the actual client over UDP.
For some baffling reason, the DatagramSocket on the serverClient never gets made, in , line 31. Its port is -1 - in the printf
I cant proceed until that is fixed.

The code is below. The server is on its own machine, along with its serverClients that it makes, and the DRWclient clients are on their own machines.

Any pointers?

Who is Participating?
krakatoaConnect With a Mentor Commented:
This illustrates how things work with DatagramSockets:


class DatagramPeer  {
        private DatagramSocket au_Send;
        static DatagramPeer dgp;
        private int port = 30314; // pop this into the DatagramSocket constructor to see diff effect

        DatagramPeer() {

            try {

                au_Send = new DatagramSocket(); // like this, the System allocates a port.

	System.out.println("DatagramPeer's socket is at address : "+this.au_Send.getLocalSocketAddress());
            } catch (SocketException exSocket) {

public static void main(String[] args){

dgp = new DatagramPeer();
PeerClass pc = new PeerClass(dgp.au_Send.getLocalSocketAddress());


static class PeerClass{

private DatagramSocket dgs;

PeerClass(SocketAddress sa){
		dgs = new DatagramSocket();dgs.connect(sa);
		System.out.println("dgs is "+dgs.isConnected()+" connected.");
		System.out.println("This inner PeerClass's socket is NOW connected, on port "+dgs.getPort());
		System.out.println("The DatagramPeer's socket is NOT connected, and so returns "+dgp.au_Send.getPort()+" for the port.");

	catch(Exception ep){ep.printStackTrace();}

	System.out.println("PeerClass is connected to remote socket at : "+dgs.getRemoteSocketAddress());
	System.out.println("PeerClass's own local socket is at address : "+dgs.getLocalSocketAddress());
	System.out.println("But now DatagramPeer's socket is connected too, and so returns "+dgp.au_Send.getPort());



Open in new window

mccarlIT Business Systems Analyst / Software DeveloperCommented:
For some baffling reason, the DatagramSocket on the serverClient never gets made, in , line 31
It's not so baffling, because it IS actually getting made, the fact that you can call .getPort() on it in the print statement means that the object is getting made.

However, you are creating the DatagramSocket "unbound" and I'm guessing what you actually mean to do is something like this...
UDPsocket = new DatagramSocket(UDPPORT);

Open in new window

ie. you have to pass the port to it that it should be listening on.
Why have you only got a DatagramSocket on one side of the connection?
7 new features that'll make your work life better

It’s our mission to create a product that solves the huge challenges you face at work every day. In case you missed it, here are 7 delightful things we've added recently to monday to make it even more awesome.

getPort() returns a port only if the UDP socket is connected. What you are looking for most likely is


which will return the port as part of the SocketAddress field.
beavoidAuthor Commented:
I like what I see. Works well!

but how much longer am I going to get away with programming this all on one machine ! !


It seems to work adequately with 2 clients. Will that very soon just become a disaster with  > 2 clients?
Can I do dev with 2 client engines on my PC; and the server on my Macbook? I can make this gameplay initially just a Jframe of 800x800, to move letters around, so that each window is in perfect synch . . until the network looks solid?

That's a much broader question of course, and we - I at least - am not familiar with the rest of your model to pass any comment. But on the face of it, having another machine dedicated to serving sounds like the better option. Maybe others here can be more helpful on this subject.
beavoidAuthor Commented:
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.