Wait and Notify
A tutorial on wait and notify; low-level thread synchronization methods in Java that allow you to avoid having vile process-consuming polling loops in your code. Code on caveofprogramming.com. Wait and notify allow you to have sleeping threads that are woken up by other threads. "Why, exactly what I've been looking for!" I hear you say. Yes, even people who don't program in Java can enjoy using these fantastic methods. OK, maybe that's going a bit far.