Exception Handling & Concurrency Flashcards

Which statement about the Error class hierarchy is correct?

Answer: Error extends Throwable directly

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

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

Answer: It unblocks all waiting threads

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

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

Answer: CancellationException

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

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

Answer: The thread's sleep is interrupted and InterruptedException is thrown

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

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

Answer: Semaphore.acquire()

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

What is the behavior of a FixedThreadPool created with Executors.newFixedThreadPool(3) when a 4th task is submitted while all 3 threads are busy?

Answer: The task is queued in an unbounded LinkedBlockingQueue

newFixedThreadPool uses an unbounded LinkedBlockingQueue, so excess tasks wait in the queue rather than being rejected or creating new threads.

Which exception type should you catch to handle both IOException and RuntimeException in a single catch block without multi-catch syntax?

Answer: Exception

Both IOException and RuntimeException extend Exception, so catching Exception covers both, though it also catches other exception subtypes.