在Java ScheduledExecutorService和FutureTask上寻求清晰度

I'm just starting to look into Futures and the ScheduledExecutorService in Java, and I'm wondering why my Callable isn't running on the schedule I've indicated. In this sample code, the callable runs once, but the app never completes, nor does the task run again, which is what I expected to happen (I'm sure the problem is with my expectation).I'm just starting to look into Futures and the