Add a simple 3 second timer to my Java source code

This is about as simple of a project as you'll find. I would like you to take my java source code and add a timer which runs every 3 seconds. Very simple! I will add some other source code inside the timer, but all I need you to do is physically create the timer and add it. The source code I have has been attached. It's an NES emulator written in java. It's several .java script files. Since I am very new to Java, I will need you to place something inside of the timer so that I can compile the source code and see that it's working (a message box or text on the screen or something).