CODEWITHSUNDEEP
javasockets
CmdrSharp
CmdrSharp

Reputation: 1070

While loop not continuing - socket

Okay, so I'm creating a rather simple java application, which will eventually turn into an online 2-player texas hold'em game. Right now, I'm trying to send some simple messages over network to make sure the basic functionality is working. I am however stuck.

I've got two methods in a class. One for the serverside (or really a hybrid between a client and a server), and one for the clientside. They connect together fine. As I made this, I noticed that when I connected, they both spammed their default messages (right now being "CLIENT: Started" and "SERVER: Started" back and forth to eachother. I figured this was because the string containing that information was never emptied, and so they never knew when to stop transmitting it. I then made sure that after sending the message, that variable was nulled, and a check was made to see if it was null before sending. Here's where it went wrong though! After doing that, they won't send more than one message at all. They send their respective welcome messages, but anything I try to transmit after that is ignored. It's almost like if the while-loop for the server/client stops.

So, I have two public variable declared in the class. These contain any message the server or client wishes to send.

public static String serverCommand = null;

public static String clientCommand = null;

They are null by default, but changed during runtime in the GUI-part. The server loop looks like this:

                while(true)
                {
                    if((receive = receiveStream.readLine()) != null)
                    {
                        System.out.println(receive);
                    }
                    if(serverCommand != null)
                    {
                        printer.println(serverCommand);
                        printer.flush();
                        Network.serverCommand = null;
                    }
                }

And the client while loop like this:

                while(true)
                {
                    if(Network.clientCommand != null)
                    {
                        printer.println(clientCommand);
                        printer.flush();
                        Network.clientCommand = null;
                    }

                    if((receive = receiveStream.readLine()) != null)
                    {
                        System.out.println(receive);
                    }
                }

However, as mentioned - after Network.clientCommand is set to null the first time around, it never again sends any messages, even though Network.clientCommand changes due to user input during runtime.

I'll post two links to the complete sourcecode of the client/server-part of this below, as they're a bit too big to paste here.

LINK: http://hastebin.com/oqotirufic.java

Does anyone here have any idea what's happening, and how should I think when trying to fix/get around it? I'll add that my experience with both Java and network programming is very limited.

EDIT

I'll add the part of the GUI which acccesses/changes the variables. http://hastebin.com/upadayuwug.java

Upvotes: 0

Views: 882

Answers (1)

Dan Getz
Dan Getz

Reputation: 9137

Of course after Network.clientCommand is null, nothing more is sent — that's what you told it to do:

if((receive = receiveStream.readLine()) != null)
{
    System.out.println(receive);
}

According to the JavaDoc, readLine() returns

A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached

Not "null if there's a pause in transmission". If it hasn't yet seen a full line, or the end of the stream (socket disconnection), well, then it's not done yet. It waits until it gets the full line of input before it goes to the next line of your code.

But how do you know if you should wait for a message to come in, or send out the next one? You can't. You can't depend on when or if anything will arrive from the other side.

What happens when both sides have nothing to send? They both start waiting to receive. What happens when one side gets something new to send? Well, once it receives something, it'll send it. But that never happens!

What you can do, is call readLine() in a separate thread. See the JavaDocs for Thread and the Java Tutorial Lesson "Concurrency". And if you're using Swing for your GUI, also see the Java Tutorial Lesson "Concurrency in Swing".

Upvotes: 2

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