Java Multithreading Objective Questions with Answers

Practice Java Multithreading MCQs with Detailed Explanations

Answer at least 12 questions to submit and verify answers.

1 Which statement about Thread.start() is correct? Easy

It directly executes run() on the current thread

It creates a new OS thread and then calls run()

It executes run() asynchronously without creating a new thread

It blocks until run() completes

2 What is the effect of calling Thread.sleep(0)? Medium

The thread sleeps forever

The thread yields execution to other threads of same priority

The thread is terminated

The thread goes into WAITING state

3 Which of the following guarantees visibility across threads without locking? Medium

synchronized

volatile

ReentrantLock

ThreadLocal

4 What happens if wait() is called without owning the object's monitor? Medium

The thread waits normally

IllegalMonitorStateException is thrown

The thread yields

The call is ignored

5 Which ExecutorService is best suited for short-lived asynchronous tasks? Medium

newSingleThreadExecutor()

newFixedThreadPool(1)

newCachedThreadPool()

newScheduledThreadPool(1)

6 Which situation can cause a deadlock? Medium

Two threads competing for CPU

Two threads holding locks in opposite order

One thread sleeping

One thread waiting on I/O

7 Which class provides atomic operations without synchronization? Medium

AtomicInteger

Integer

LongAdder

ThreadLocal

8 What is the main benefit of using LongAdder over AtomicLong? High

Lower memory usage

Better performance under high contention

Stronger consistency

Faster single-threaded performance

9 What state is a thread in after calling wait()? Medium

RUNNABLE

WAITING

TIMED_WAITING

BLOCKED

10 Which method ensures all previously submitted tasks are completed before returning? Medium

shutdown()

shutdownNow()

awaitTermination()

close()

11 Which is true about synchronized blocks? Medium

They lock the entire class always

They lock only the current thread

They lock a specific monitor object

They are reentrant only for static methods

12 What does ThreadLocal provide? Medium

Shared variable across threads

Thread-confined variables

Atomic operations

Lock-free synchronization

13 Which is NOT a benefit of using Executors? Medium

Thread reuse

Task queueing

Better resource management

Guaranteed task execution order across multiple threads

14 What happens if a thread throws an unchecked exception? Medium

JVM terminates

The thread dies and exception is sent to uncaught handler

All threads stop

The exception is ignored

15 Which mechanism supports fairness in locking? High