1Z0-819 Exception Handling & Concurrency 5

Question 1

Which statement about the Error class hierarchy is correct?

Accepted Answer

Error extends Throwable directly

Answer

Error extends Throwable directly (not Exception), and errors like OutOfMemoryError and StackOverflowError represent serious JVM-level problems.

Question 2

What does CountDownLatch.await() do when the count reaches zero?

Accepted Answer

It unblocks all waiting threads

Answer

When countDown() reduces the latch's count to zero, all threads blocked on await() are released simultaneously.

Question 3

Which exception is thrown when you call Future.get() on a cancelled task?

Accepted Answer

CancellationException

Answer

Calling get() on a Future that was cancelled via cancel(true) causes CancellationException to be thrown.

Question 4

What is the effect of calling Thread.interrupt() on a thread that is currently sleeping?

Accepted Answer

The thread's sleep is interrupted and InterruptedException is thrown

Answer

Interrupting a sleeping thread causes the sleep to terminate early by throwing InterruptedException and clearing the thread's interrupt status.

Question 5

Which method of Semaphore acquires a permit, blocking until one is available?

Accepted Answer

Semaphore.acquire()

Answer

Semaphore.acquire() decrements the permit count, blocking if no permits are available until another thread calls release().

(1Z0-819) Oracle Java SE 11 Developer Practice Test