About Question enthuware.ocpjp.ii.v11.2.1256 :

[sheldon_si]

An ExecutorService that can schedule commands to run after a given delay, or to execute periodically. The schedule methods create tasks with various delays and return a task object that can be used to cancel or check execution. The scheduleAtFixedRate and scheduleWithFixedDelay methods create and execute tasks that run periodically until cancelled.

there is a typing error on ExecutorService, it should be ScheduledExecutorService according to the description you have provided.

[admin]

No, it is not an error. This comment is for ScheduledExecutorService and is written under that heading. ScheduledExecutorService is an ExecutorService. That is why, the comment starts that way.