Java developers

I know there are plenty of tutorials and such on JBoss out there. In fact, you could say there are to many.
Any suggestions on some decent ones? I'm looking for one that isn't to basic but is not too advanced either. It would be used to educate a group of developers who have never used JBoss, or J2EE either?

Consider an instant message GUI (note: this is not exactly what i'm writing, but the best description I can give). There is an input box for typing messages to another computer (JTextField) and an output field for recieving (JTextArea).

The problem I'm having is that my theory on writing this started with the idea that someone would send a message, and then recieve a message, which obviously is not that case, as sometimes you'll send 4 messages before you recieve one, and vice versa. If I let the program "hang" until it recieves a message it locks up the GUI until it recieves said message, making it impossible to input anything. Is there any way around this, specifically two seperate chunks of code running at the same time, allowing two seperate things to be happening?

I've tried googling, but this isn't the easiest thing to describe in a short string.

I know this may well be an inanely noob question to ask but here goes:

I have a Canvas class object declared which contains an overridden "paint()" method.
Within that paint method I need to make lines which will be positioned according to the member values of objects stored in an array.

The Canvas object is declared within the application class, and instantiated in the initialization of the application.
The objects in the array and which contain the values needed by the paint() method are also declared within the application class, and instantiated in the initialization of the application.

Yet somehow I can't make the object members of the array "resolveable". There's just no way eclipse will let me make the two work together. Something to do with variable or object scope.

I hope you have some help available on this as to what I've done wrong or what's wrong with my thinking/knowledge.

Thanks,
Dom