OCP Java Concurrency 2

Question 1

Which method of the `CountDownLatch` class blocks the calling thread until the count reaches zero?

Accepted Answer

await()

Answer

`await()` blocks the current thread until the latch's count reaches zero, while `countDown()` decrements the count.

Question 2

What happens when a thread calls `CyclicBarrier.await()` and it is the last thread to arrive at the barrier?

Accepted Answer

It triggers the optional barrier action and releases all waiting threads

Answer

The last thread to call `await()` optionally runs the barrier action, then all waiting threads are released.

Question 3

Which `ExecutorService` method submits a `Callable` and returns a `Future` representing the pending result?

Accepted Answer

submit(Callable)

Answer

`submit(Callable)` accepts a `Callable` and returns a `Future<T>` that can be used to retrieve the result.

Question 4

What is the purpose of the `volatile` keyword in Java concurrency?

Accepted Answer

Ensures visibility of variable changes across threads without atomicity guarantees

Answer

`volatile` guarantees that reads/writes go directly to main memory, ensuring visibility, but does not provide atomicity for compound operations.

Question 5

Which class in `java.util.concurrent` provides a resizable-array implementation of a blocking queue?

Accepted Answer

LinkedBlockingQueue

Answer

`LinkedBlockingQueue` is backed by linked nodes and can optionally be bounded, while `ArrayBlockingQueue` uses a fixed-size array.

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