OCP Java Concurrency 4

Question 1

Which `Phaser` method allows a thread to arrive at a phase and deregister itself from future phases?

Accepted Answer

arriveAndDeregister()

Answer

`arriveAndDeregister()` records arrival and reduces the registered party count, so the thread no longer participates in subsequent phases.

Question 2

What distinguishes `ScheduledThreadPoolExecutor` from a regular `ThreadPoolExecutor`?

Accepted Answer

It can schedule commands to run after a delay or periodically

Answer

`ScheduledThreadPoolExecutor` adds the ability to schedule tasks with fixed-delay, fixed-rate, or one-shot delay execution.

Question 3

When using `synchronized` on an instance method, which object is used as the monitor lock?

Accepted Answer

The instance (`this`) on which the method is called

Answer

An instance `synchronized` method acquires the intrinsic lock on `this`, the object the method is invoked on.

Question 4

Which scenario can cause a `ConcurrentModificationException` in a non-concurrent collection?

Accepted Answer

Modifying a collection while iterating over it with a for-each loop

Answer

Structurally modifying a collection outside of the iterator's own `remove()` during iteration triggers a `ConcurrentModificationException`.

Question 5

What is the key difference between `ReentrantLock` and `ReentrantReadWriteLock`?

Accepted Answer

ReadWriteLock allows multiple concurrent readers but only one writer at a time

Answer

`ReentrantReadWriteLock` separates read and write locks, allowing concurrent reads but exclusive writes for better throughput in read-heavy workloads.

(OCP) Oracle Certified Professional Practice Test

(OCP) Oracle Certified Professional Practice Test

OCP Java Concurrency 4