Enthuware

The exam has questions that require you to know valid states but it is not clear whether invalid is considered a state or not.

Agreed that the API docs are not clear on this topic. But for the record, Oracle's official tutorial docs do list it as three states:

A watch key has a state. At any given time, its state might be one of the following:

• Ready indicates that the key is ready to accept events. When first created, a key is in the ready state.
• Signaled indicates that one or more events are queued. Once the key has been signaled, it is no longer in the ready state until the reset method is invoked.
• Invalid indicates that the key is no longer active. This state happens when one of the following events occurs:
  • ◦ The process explicitly cancels the key by using the cancel method.
    ◦ The directory becomes inaccessible.
    ◦ The watch service is closed.

https://docs.oracle.com/javase/tutorial ... ml#process

From the look of it I think I would be inclined to count it as one if the question were to come up.

That is a good point. We will leave it open so that other readers may make their own informed decision.
-Paul.