Java Multithreading Objective Questions and Answers - Set 2

Test your skills in Java multithreading with carefully curated objective questions including output-based MCQs. Ideal for interview preparation and mastering concurrency concepts such as synchronization, executors, locks, atomic variables, deadlocks, and performance tuning. This is part 2 of the series.

Practice Java Multithreading MCQs with Detailed Explanations

Answer at least 12 questions to submit and verify answers.

16 What is a livelock? High

Threads are blocked forever

Threads are dead but CPU is idle

Threads keep changing state but make no progress

Threads are waiting on I/O

17 Which method can interrupt a thread? Medium

interrupt()

stop()

yield()

notify()

18 What is the effect of calling notify()? Medium

All waiting threads are woken up

One arbitrary waiting thread is woken up

The current thread sleeps

The monitor is released permanently

19 Which is true about volatile writes? High

They are atomic for all operations

They establish a happens-before relationship

They block other threads

They guarantee mutual exclusion

20 What is the purpose of CountDownLatch? Medium

Limit concurrent threads

Coordinate threads by waiting for a count to reach zero

Provide mutual exclusion

Schedule tasks periodically

21 Which is best for limiting concurrent access to a resource? Medium

Semaphore

CountDownLatch

CyclicBarrier

Future

22 What is a ForkJoinPool optimized for? High

Long-running blocking I/O tasks

CPU-bound recursive divide-and-conquer tasks

Single-thread execution

Scheduled tasks

23 Which method submits a task and returns a Future? Medium

execute()

submit()

invoke()

run()

24 What happens if two threads call join() on each other? High

Both terminate normally

Deadlock

One thread yields

RuntimeException

25 Which collection is thread-safe without external synchronization? Medium

ArrayList

CopyOnWriteArrayList

HashMap

LinkedList

26 Which problem is caused by instruction reordering? High

Race condition

Visibility issues

Deadlock

Starvation

27 What is the default behavior of ReentrantLock? Medium

Fair locking

Unfair locking

Read-write locking

Spin locking

28 Which construct allows multiple readers but single writer? Medium

synchronized

ReentrantLock

ReadWriteLock

Semaphore

29 What is thread starvation? Medium

Thread consumes too much CPU

Thread never gets CPU due to scheduling or locks

Thread is blocked forever

Thread is waiting on I/O

30 What is the output? int x = 0; Thread t1 = new Thread(() -> x++); Thread t2 = new Thread(() -> x++); t1.start(); t2.start(); Thread.sleep(100); System.out.println(x); High

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