wait vs. yield?

I've looked at this: http://bit.ly/9GqZoT but still have some
doubts... I'm implementing a thread pool containing multiple threads,
which are created when the application starts, and then they hang
around waiting to be given a job to do. It involves a loop as follows
or similar:

while (true) {
  while (job == null)
    // wait
  // and then do the job:
  job.run();
  job = null; // the job is done
}

Another method exist to submit the job to this pool thread. It means a
method which perform the assignment:
job = new SomeJobToDo();

The problem is how to perform the "wait" operation. For just poor
esthetic reasons I prefer using the Thread.yield() or eg.
Thread.sleep(500) method. But examples I found in the Internet tend to
use another object (let's say lock) and its Object.wait() method. This
causes that the Object.notify() method must be invoked after ordering
the job (the assignment).

My questions:
1) Which one of these two basic methods is better and, which is more
important for my, WHY?
2) What is better: using sleep or yield in the first method?