75+ Java Multithreading Interview Questions & Answers (2025 Basic to Advanced)

Multithreading and concurrency are among the toughest topics in Java interviews and also the most important. If you’re preparing for a Java developer role in 2025, chances are your interviewer will grill you on threads, synchronization, deadlocks, parallelism, and the latest features like Completable Future and Virtual Threads.

But here’s the problem: most resources online are either too shallow (just definitions) or outdated (ignoring new Java concurrency features). That’s why we created this ultimate guide with 75+ Java multithreading interview questions and detailed answers carefully structured into basic, intermediate, and advanced sections.

Whether you’re refreshing fundamentals, tackling real-world concurrency scenarios, or showcasing knowledge of Project Loom, this guide will help you:

Master tricky multithreading concepts with examples and best practices.
Avoid common pitfalls like race conditions, deadlocks, and thread leaks.
Stand out in interviews by explaining not just what but why and how.

By the end, you won’t just memorize answers you’ll gain the confidence to handle any multithreading question thrown your way.

Table of Contents

Basic-Level Java Multithreading Interview Questions

These are the fundamental questions every interviewer expects you to know. They test whether you understand the core building blocks of Java threads and concurrency.

What is multithreading in Java?

Multithreading is the ability of a program to execute multiple threads simultaneously, enabling parallelism and efficient CPU utilization.

Thread → smallest unit of execution inside a process.
Multithreading allows different parts of a program (e.g., UI updates, background tasks, network calls) to run concurrently.
In Java, threads share the same heap memory of a process but maintain their own stack.

Benefits:

Better CPU utilization
Responsiveness in applications
Enables asynchronous programming

Pitfalls:

Race conditions, deadlocks, synchronization overhead

What is the difference between a process and a thread?

Process: An independent program with its own memory space.
Thread: A lightweight unit of execution within a process, sharing the process memory but maintaining its own stack.

Key differences:

Process is heavyweight; thread is lightweight.
Inter-process communication is costly; inter-thread communication is easier.
Context switching between processes is slower than between threads.

How can you create a thread in Java?

Java provides multiple ways:

Extending Thread class

class MyThread extends Thread {
    public void run() {
        System.out.println("Thread running");
    }
}
new MyThread().start();

Implementing Runnable interface

class MyTask implements Runnable {
    public void run() {
        System.out.println("Runnable running");
    }
}
new Thread(new MyTask()).start();

Using Callable with Future

Callable<Integer> task = () -> 42;
Future<Integer> result = Executors.newSingleThreadExecutor().submit(task);

Using Executors framework → recommended for production.

What is the lifecycle of a thread in Java?

Java threads go through the following states (Thread.State):

NEW → Created but not started.
RUNNABLE → Eligible to run but waiting for CPU scheduling.
RUNNING → Actively executing on CPU.
BLOCKED → Waiting for a monitor lock.
WAITING → Waiting indefinitely until notified.
TIMED_WAITING → Waiting for a limited time (sleep, join with timeout).
TERMINATED → Completed execution.

What happens if you call `run()` instead of `start()`?

start() → Creates a new thread and executes run() inside it.
run() → Executes in the current thread like a normal method call, no new thread is created.

Interview trap: Many candidates incorrectly say both are the same – be clear that start() is essential for true concurrency.

What is the difference between `Runnable` and `Callable`?

Runnable → run() returns no result, cannot throw checked exceptions.
Callable → call() returns a result and can throw checked exceptions.

When to use?

Use Runnable for fire-and-forget tasks.
Use Callable when you need a return value or error handling.

What is the `synchronized` keyword used for?

synchronized ensures that only one thread at a time can access a critical section.

Example:

public synchronized void increment() {
    counter++;
}

Guarantees:

Mutual exclusion → Only one thread executes at a time.
Visibility → Changes are visible to other threads after lock release.

What is the difference between `synchronized` method and synchronized block?

Synchronized method → Locks the entire method (on this or class object for static).
Synchronized block → Locks only the specified section of code.

Best practice: Use synchronized blocks for fine-grained locking to reduce contention.

What is a race condition?

A race condition occurs when multiple threads access and modify shared data simultaneously, and the final result depends on the timing of execution.

Example:

count++; // not atomic

Two threads might read, increment, and write back incorrect values.

Solution: Use synchronization, AtomicInteger, or locks.

What is `volatile` in Java?

Ensures visibility: all reads/writes go directly to main memory.
Prevents instruction reordering.
Does not guarantee atomicity.

Example use:

volatile boolean running = true;

Used for flags and state indicators, not compound operations.

What is the difference between `wait()`, `sleep()`, and `join()`?

wait() → Releases lock, waits for notification (notify()/notifyAll()).
sleep() → Pauses thread for specified time, does not release lock.
join() → Current thread waits until another thread finishes.

What is thread priority in Java?

Every thread has a priority (1–10). Higher priority threads are scheduled before lower priority ones, but scheduling is JVM/OS dependent.

Tip: Don’t rely on thread priority for correctness; use proper synchronization.

What is the difference between `isAlive()` and `join()`?

isAlive() → Returns true if thread has started and not finished.
join() → Blocks current thread until the target thread finishes.

What is the difference between daemon and user threads?

User thread → Keeps JVM alive until all user threads finish.
Daemon thread → Background threads (e.g., GC). JVM exits when only daemon threads remain.

Example:

Thread t = new Thread(task);
t.setDaemon(true);

What is thread safety?

A class is thread-safe if multiple threads can access it simultaneously without breaking invariants or producing incorrect results.

Examples:

Thread-safe: Vector, ConcurrentHashMap
Not thread-safe: ArrayList, HashMap

What are thread pools in Java?

A thread pool is a collection of worker threads managed by ExecutorService.

Benefits:

Reuse threads → avoid overhead
Control concurrency
Better resource management

Example:

ExecutorService pool = Executors.newFixedThreadPool(5);
pool.submit(() -> System.out.println("Task running"));

What is deadlock in Java?

Deadlock occurs when two or more threads wait indefinitely for locks held by each other.

Example scenario:

Thread A locks resource1, waits for resource2
Thread B locks resource2, waits for resource1

Solution strategies:

Acquire locks in consistent order
Use tryLock() with timeout
Minimize nested locks

What is livelock?

Livelock occurs when threads are not blocked, but keep changing state in response to each other, and no progress is made.

Example: Two threads repeatedly yielding to each other.

What is thread starvation?

Starvation happens when a thread never gets CPU time or resources because higher-priority threads dominate.

Fix:

Use fair locks (new ReentrantLock(true))
Avoid priority misuse

What is the difference between concurrency and parallelism?

Concurrency → Multiple tasks progress overlapping in time, but not necessarily simultaneously.
Parallelism → Tasks execute at the same time (true parallel execution on multi-core CPUs).

What is context switching in multithreading?

Context switching is when the CPU switches from one thread to another, saving the current thread’s state and loading another’s.

Lightweight compared to processes, but still costly if excessive.

What are thread groups?

Thread groups are used to manage multiple threads as a group.

ThreadGroup group = new ThreadGroup("MyGroup");
Thread t = new Thread(group, task);

Rarely used today, but still part of Java API.

What is `Thread.yield()`?

A hint to the scheduler that the thread is willing to yield CPU.
Does not guarantee immediate switch – depends on JVM/OS.

What are the differences between `notify()` and `notifyAll()`?

notify() → Wakes one waiting thread.
notifyAll() → Wakes all waiting threads.

Tip: Use notifyAll() to avoid missed notifications and starvation.

Why should we avoid using `Thread.stop()`?

It abruptly terminates a thread without releasing locks → causes inconsistent state.
Deprecated and unsafe.
Better alternative: use a volatile flag or interruption mechanism.

Intermediate-Level Java Multithreading Interview Questions

These questions go beyond the basics and test whether you can design and reason about concurrency in real-world Java applications.

What are the drawbacks of creating a new thread for each task?

Creating a new thread for every task seems simple but is inefficient:

High overhead → Thread creation consumes memory and OS resources.
Context switching cost → Too many threads degrade performance.
Unbounded growth → Can exhaust memory or CPU.
Lack of control → No easy way to throttle tasks.

Best practice: Use thread pools (ExecutorService) to manage tasks efficiently.

What is the Executor framework in Java?

The Executor framework decouples task submission from thread management.

Executor → Interface with execute(Runnable task)
ExecutorService → Extends Executor, adds lifecycle management (submit, shutdown)
Executors → Factory methods to create thread pools

Example:

ExecutorService executor = Executors.newFixedThreadPool(5);
executor.submit(() -> System.out.println("Task running"));
executor.shutdown();

This improves scalability and avoids manual thread handling.

What is the difference between `submit()` and `execute()` in ExecutorService?

execute(Runnable) → Returns void. Fire-and-forget.
submit(Runnable/Callable) → Returns a Future that can hold a result or exception.

When to use?

Use execute for tasks that don’t need a result.
Use submit when you need a return value or exception handling.

What is a Future in Java?

Future represents the result of an asynchronous computation.

Key methods:

get() → Waits for result
isDone() → Checks if computation finished
cancel() → Attempts to cancel task

Limitation: Future blocks on get() and lacks chaining.
Solution: Use CompletableFuture for more advanced composition.

What is a CompletableFuture?

CompletableFuture (Java 8) is an advanced Future that supports:

Asynchronous execution (supplyAsync, runAsync)
Chaining (thenApply, thenAccept, thenRun)
Combining multiple futures (allOf, anyOf)
Exception handling (exceptionally, handle)

Example:

CompletableFuture.supplyAsync(() -> "Hello")
    .thenApply(s -> s + " World")
    .thenAccept(System.out::println);

What is a ReentrantLock?

ReentrantLock is an explicit lock with more capabilities than synchronized:

Can try lock (tryLock())
Supports fair locking (new ReentrantLock(true))
Allows interruptible lock acquisition
Provides Condition variables for fine-grained waiting

Example:

ReentrantLock lock = new ReentrantLock();
lock.lock();
try {
   // critical section
} finally {
   lock.unlock();
}

What is the difference between `synchronized` and `ReentrantLock`?

synchronized → Implicit, simple, automatic release, less flexible.
ReentrantLock → Explicit, must release manually, supports timeout, fairness, and multiple condition queues.

Rule of thumb: Use synchronized for simplicity, ReentrantLock for advanced control.

What are ReadWriteLocks?

ReadWriteLock allows multiple threads to read simultaneously but only one writer at a time.

ReentrantReadWriteLock → common implementation
Improves performance in read-heavy workloads

Example:

ReadWriteLock rwLock = new ReentrantReadWriteLock();
rwLock.readLock().lock();
try {
   // multiple readers allowed
} finally {
   rwLock.readLock().unlock();
}

What is StampedLock?

StampedLock (Java 8) is a lock that supports:

Read lock
Write lock
Optimistic read → read without blocking, then validate

Optimistic reads reduce contention in read-mostly scenarios.

What are atomic classes in Java?

Located in java.util.concurrent.atomic, these classes provide lock-free, thread-safe operations using CAS (Compare-And-Swap).

Examples:

AtomicInteger → incrementAndGet()
AtomicReference<T> → compareAndSet(expected, update)

They are faster than synchronization for simple variable updates.

What is CAS (Compare-And-Swap)?

CAS is a low-level atomic instruction:

Reads current value
Compares it with expected value
If equal → updates with new value
Else → retries

CAS avoids locks and enables non-blocking algorithms.

What is a BlockingQueue?

BlockingQueue is a thread-safe queue that blocks producers if full and consumers if empty.

Implementations:

ArrayBlockingQueue
LinkedBlockingQueue
PriorityBlockingQueue

Example:

BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(10);
queue.put(1);  // blocks if full
int val = queue.take(); // blocks if empty

How do you implement Producer-Consumer in Java?

Using BlockingQueue (preferred):

BlockingQueue<Integer> queue = new LinkedBlockingQueue<>(10);

// Producer
executor.submit(() -> {
    queue.put(42);
});

// Consumer
executor.submit(() -> {
    System.out.println(queue.take());
});

This avoids manual wait()/notify() complexity.

What is the difference between `ConcurrentHashMap` and `HashMap`?

HashMap → Not thread-safe, can cause corruption in multithreaded environments.
ConcurrentHashMap → Thread-safe, uses lock striping for scalability, allows concurrent reads and updates.

What is CopyOnWriteArrayList?

A thread-safe variant of ArrayList.
On modification, it creates a new copy of the underlying array.
Ideal for read-heavy workloads with infrequent writes.

Downside: High memory cost for frequent writes.

What is ThreadLocal in Java?

ThreadLocal<T> provides thread-specific variables. Each thread gets its own copy.

Use cases:

Per-thread context (e.g., database connections, user sessions)
Avoid passing variables across multiple layers

Caution: Must call remove() to prevent memory leaks in thread pools.

What is the difference between `notify()` and `notifyAll()`?

notify() → Wakes a single waiting thread
notifyAll() → Wakes all waiting threads

Best practice: Use notifyAll() to avoid missed signals.

What is a Semaphore?

A Semaphore controls access to resources via permits.

Example:

Semaphore sem = new Semaphore(3); // 3 permits
sem.acquire();  // acquire permit
try {
   // critical section
} finally {
   sem.release();
}

Useful for limiting concurrent access (e.g., DB connections).

What is a CountDownLatch?

CountDownLatch allows one or more threads to wait until a set of operations complete.

Example:

CountDownLatch latch = new CountDownLatch(3);
executor.submit(() -> { task(); latch.countDown(); });
latch.await(); // waits until count reaches zero

What is a CyclicBarrier?

CyclicBarrier allows a group of threads to wait for each other at a barrier point.

Unlike CountDownLatch, it can be reused.
Useful in parallel algorithms (e.g., matrix computations).

What is Phaser in Java?

Phaser is a flexible synchronization barrier that supports multiple phases.

Dynamic registration of parties
More powerful than CyclicBarrier

What is the difference between CountDownLatch and CyclicBarrier?

CountDownLatch → One-time use, threads wait for others to finish.
CyclicBarrier → Reusable, threads wait for each other to reach the barrier.

What is ExecutorService shutdown?

shutdown() → Graceful shutdown, no new tasks accepted.
shutdownNow() → Attempts to stop running tasks immediately.
awaitTermination(timeout) → Waits for tasks to finish after shutdown.

What is ForkJoinPool?

Designed for divide-and-conquer tasks (work-stealing).
Splits large tasks into subtasks (fork), then merges results (join).
Used internally in parallelStream().

What are parallel streams in Java 8?

Streams that divide workload across multiple threads using ForkJoinPool.
Example:

list.parallelStream()
    .map(String::toUpperCase)
    .forEach(System.out::println);

Great for data-parallel operations but avoid for I/O-bound tasks.

Advanced & Scenario-Based Java Multithreading Interview Questions

This section focuses on real-world challenges, tricky scenarios, modern Java features (CompletableFuture, Virtual Threads, etc.), and debugging concurrency issues.

How do you detect and debug deadlocks in Java?

Deadlocks can be detected by analyzing thread dumps:

Use jstack <pid> or kill -3 <pid> (Linux) to capture thread dump.
Look for threads in BLOCKED state waiting for locks.
IDEs and tools like VisualVM or JConsole can also highlight deadlocks.

Programmatic detection:

ThreadMXBean bean = ManagementFactory.getThreadMXBean();
long[] ids = bean.findDeadlockedThreads();

What strategies help prevent deadlocks?

Lock ordering → Acquire locks in a consistent global order.
Timeouts → Use tryLock(timeout) instead of blocking.
Minimize lock scope → Reduce time spent holding locks.
Use higher-level constructs → ConcurrentHashMap, BlockingQueue.

What is livelock and how do you handle it?

In livelock, threads are not blocked but keep retrying and preventing each other’s progress.
Example: Two threads repeatedly yielding to avoid collision.
Solution: Add randomness, backoff strategies, or proper coordination.

What is starvation and how do you prevent it?

Starvation happens when a thread never gets CPU or resources.
Causes: unfair locks, high-priority threads dominating.
Fix: Use fair locks (new ReentrantLock(true)) or avoid priority misuse.

What is the Java Memory Model (JMM)?

The JMM defines how threads interact through memory:

Rules for visibility, ordering, and atomicity.
Guarantees via volatile, synchronized, and final fields.
Defines happens-before relationships.

Example: A volatile write happens-before subsequent reads.

What is happens-before in Java concurrency?

If operation A happens-before operation B, then:

A’s effects are visible to B.
No reordering across A and B.

Examples:

Unlock → happens-before → subsequent lock on the same monitor.
Thread start → happens-before → run() execution.
Thread completion → happens-before → join().

What is false sharing in multithreading?

Occurs when multiple threads update independent variables that reside in the same CPU cache line.
Causes performance degradation due to cache invalidations.
Fix: Use padding (@Contended annotation in Java 8+).

What is lock contention and how do you reduce it?

Lock contention happens when multiple threads compete for the same lock.

Solutions:

Reduce synchronized blocks.
Use fine-grained locks.
Use concurrent data structures.
Consider lock-free algorithms.

What are non-blocking algorithms?

Algorithms that use CAS (Compare-And-Swap) instead of locks.
Lock-free → At least one thread always makes progress.
Wait-free → All threads make progress in bounded steps.

Examples:

ConcurrentLinkedQueue
AtomicInteger

How does Java handle thread interruption?

interrupt() → sets the thread’s interrupted flag.
Thread checks Thread.interrupted() or throws InterruptedException if blocking.

Best practice: Always restore the interrupt status when catching InterruptedException:

catch (InterruptedException e) {
   Thread.currentThread().interrupt();
}

How would you implement a thread-safe Singleton?

Using double-checked locking:

class Singleton {
    private static volatile Singleton instance;
    private Singleton() {}
    public static Singleton getInstance() {
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null) instance = new Singleton();
            }
        }
        return instance;
    }
}

volatile prevents reordering issues.

How do you safely stop a thread in Java?

Don’t use Thread.stop().
Use a volatile flag:

volatile boolean running = true;
public void run() {
   while (running) { /* work */ }
}

Or use interruption with Thread.interrupt().

How would you implement Producer-Consumer without BlockingQueue?

Using wait/notify:

class Buffer {
   private Queue<Integer> queue = new LinkedList<>();
   private int capacity = 10;

   public synchronized void produce(int val) throws InterruptedException {
      while (queue.size() == capacity) wait();
      queue.add(val);
      notifyAll();
   }

   public synchronized int consume() throws InterruptedException {
      while (queue.isEmpty()) wait();
      int val = queue.remove();
      notifyAll();
      return val;
   }
}

What are Fork/Join tasks and when do you use them?

Fork/Join splits tasks into subtasks, runs them in parallel, then merges results.
Suitable for divide-and-conquer problems.
Example: parallel sum of array using RecursiveTask.

How does work-stealing in ForkJoinPool work?

Idle threads steal tasks from busy threads’ queues.
Improves load balancing.
Reduces bottlenecks in recursive parallelism.

How do parallel streams work internally?

Backed by ForkJoinPool.commonPool().
Automatically splits data into chunks.
Tasks run in parallel across threads.

Caution: Not ideal for I/O tasks or small collections due to overhead.

How would you design a system to fetch results from multiple APIs concurrently?

Using CompletableFuture:

CompletableFuture<String> api1 = fetchAsync("url1");
CompletableFuture<String> api2 = fetchAsync("url2");

CompletableFuture.allOf(api1, api2)
    .thenApply(v -> api1.join() + api2.join())
    .thenAccept(System.out::println);

Supports parallel execution, fallback handling, and composition.

How do you set timeouts in concurrent tasks?

future.get(timeout, TimeUnit.SECONDS)
CompletableFuture.orTimeout() (Java 9+)
ExecutorService.invokeAny() with timeout.

What are virtual threads in Project Loom?

Introduced in Java 21.
Lightweight threads scheduled by JVM, not OS.
Millions of virtual threads possible.
Simplifies concurrency by allowing blocking calls without heavy cost.

How do virtual threads differ from platform threads?

Platform threads → one-to-one mapping with OS threads.
Virtual threads → multiplexed on fewer carrier threads.
Virtual threads are cheap to create, block, and manage.

How do you migrate existing code to virtual threads?

Replace thread pools with Executors.newVirtualThreadPerTaskExecutor().
Avoid thread-local leaks.
Ensure blocking operations are compatible (JVM handles most).

How would you debug performance issues in a multithreaded app?

Capture thread dumps.
Analyze lock contention with JFR/JMC.
Use profiling tools (VisualVM, YourKit).
Measure queue wait times, task execution times.
Look for excessive context switching.

How do you design for scalability in multithreaded systems?

Use non-blocking structures (ConcurrentLinkedQueue).
Use partitioning (sharding) to reduce contention.
Apply backpressure mechanisms.
Avoid global locks; use fine-grained or lock-free approaches.

What is reactive programming and how does it compare to multithreading?

Reactive programming is event-driven, asynchronous, non-blocking.
Uses reactive libraries (Reactor, RxJava, Flow API).
Scales better than blocking threads for I/O-heavy systems.

What concurrency improvements came in recent Java versions?

Java 8 → CompletableFuture, StampedLock, parallel streams.
Java 9 → Flow API (reactive streams).
Java 21 → Virtual threads (Project Loom).

Tips to Ace Java Multithreading Interviews

Mastering answers is only half the battle – how you present and think aloud during interviews makes a huge difference. Here are pro tips:

Explain trade-offs → Don’t just give an API name, explain why you’d use ReentrantLock over synchronized.
Draw diagrams → For race conditions, deadlocks, and thread states, use whiteboard sketches if asked.
Show awareness of modern Java → Mention CompletableFuture, Flow API, Virtual Threads. Interviewers love candidates who stay current.
Talk about pitfalls → Example: “Using volatile ensures visibility but not atomicity, so for compound operations I’d use AtomicInteger or locks.”
Think about performance → Mention contention, false sharing, scalability under load.
Use real-world scenarios → Example: “In a web server, I’d use a cached thread pool to handle variable requests efficiently.”

Common Mistakes Candidates Make

Confusing run() vs start() – forgetting that start() creates a new thread.
Overusing synchronized – leading to contention and bottlenecks.
Ignoring interruption – not restoring interrupt status in catch.
ThreadLocal leaks – forgetting to remove() in thread pools.
Using deprecated methods (Thread.stop(), suspend()).
Forgetting happens-before rules – explaining concurrency without memory visibility.
Overreliance on parallel streams – without considering workload type (CPU vs I/O).

Advanced Resources for Mastery

If you want to go beyond interview prep and build true concurrency expertise, explore:

[Java Concurrency in Practice – Brian Goetz] (industry bible)
Official Java Concurrency Tutorial (Oracle Docs)
Baeldung’s Concurrency Articles
JCStress – for testing concurrency correctness
Blogs on Project Loom (Virtual Threads)

Related Java Interview Guides

Conclusion

Multithreading in Java is not just an interview topic – it’s the backbone of high-performance, scalable systems. Interviewers use it to test not just coding ability, but your system design thinking, debugging skills, and real-world problem-solving.

By practicing these 75+ Java multithreading interview questions and answers, you’ve:

Strengthened your fundamentals (thread lifecycle, synchronization, race conditions).
Learned intermediate concepts (Executor framework, concurrency utilities, atomic classes).
Tackled advanced, scenario-based challenges (deadlocks, ForkJoinPool, CompletableFuture, Virtual Threads).

The key takeaway: don’t just memorize. Think in terms of why, how, trade-offs, and best practices. That’s what separates a good candidate from a great one.

FAQ

Is Java multithreading still relevant in 2025?

Yes. Even with Virtual Threads (Project Loom), understanding traditional threading, locks, and concurrency pitfalls remains critical for interviews and production systems.

What’s the best way to prepare for Java multithreading interviews?

Practice writing code (producer-consumer, deadlock detection), study the Java Memory Model, and understand new features like CompletableFuture and Virtual Threads.

What is the toughest multithreading interview question?

Usually scenario-based: designing a thread-safe system, debugging deadlocks from a thread dump, or explaining the happens-before rules with examples.

Do I need to know Project Loom for interviews?

Yes – especially in 2025. Even if companies haven’t adopted it fully, showing awareness of Virtual Threads demonstrates that you stay updated.

Basic-Level Java Multithreading Interview Questions

What is multithreading in Java?

What is the difference between a process and a thread?

How can you create a thread in Java?

What is the lifecycle of a thread in Java?

What happens if you call run() instead of start()?

What is the difference between Runnable and Callable?

What is the synchronized keyword used for?

What is the difference between synchronized method and synchronized block?

What is a race condition?

What is volatile in Java?

What is the difference between wait(), sleep(), and join()?

What is thread priority in Java?

What is the difference between isAlive() and join()?

What is the difference between daemon and user threads?

What is thread safety?

What are thread pools in Java?

What is deadlock in Java?

What is livelock?

What is thread starvation?

What is the difference between concurrency and parallelism?

What is context switching in multithreading?

What are thread groups?

What is Thread.yield()?

What are the differences between notify() and notifyAll()?

Why should we avoid using Thread.stop()?

Intermediate-Level Java Multithreading Interview Questions

What are the drawbacks of creating a new thread for each task?

What is the Executor framework in Java?

What is the difference between submit() and execute() in ExecutorService?

What is a Future in Java?

What is a CompletableFuture?

What is a ReentrantLock?

What is the difference between synchronized and ReentrantLock?

What are ReadWriteLocks?

What is StampedLock?

What are atomic classes in Java?

What is CAS (Compare-And-Swap)?

What is a BlockingQueue?

How do you implement Producer-Consumer in Java?

What is the difference between ConcurrentHashMap and HashMap?

What is CopyOnWriteArrayList?

What is ThreadLocal in Java?

What is the difference between notify() and notifyAll()?

What is a Semaphore?

What is a CountDownLatch?

What is a CyclicBarrier?

What is Phaser in Java?

What is the difference between CountDownLatch and CyclicBarrier?

What is ExecutorService shutdown?

What is ForkJoinPool?

What are parallel streams in Java 8?

Advanced & Scenario-Based Java Multithreading Interview Questions

How do you detect and debug deadlocks in Java?

What strategies help prevent deadlocks?

What is livelock and how do you handle it?

What is starvation and how do you prevent it?

What is the Java Memory Model (JMM)?

What is happens-before in Java concurrency?

What is false sharing in multithreading?

What is lock contention and how do you reduce it?

What are non-blocking algorithms?

How does Java handle thread interruption?

How would you implement a thread-safe Singleton?

How do you safely stop a thread in Java?

How would you implement Producer-Consumer without BlockingQueue?

What are Fork/Join tasks and when do you use them?

How does work-stealing in ForkJoinPool work?

How do parallel streams work internally?

How would you design a system to fetch results from multiple APIs concurrently?

How do you set timeouts in concurrent tasks?

What are virtual threads in Project Loom?

How do virtual threads differ from platform threads?

How do you migrate existing code to virtual threads?

How would you debug performance issues in a multithreaded app?

How do you design for scalability in multithreaded systems?

What is reactive programming and how does it compare to multithreading?

What concurrency improvements came in recent Java versions?

Tips to Ace Java Multithreading Interviews

Common Mistakes Candidates Make

What happens if you call `run()` instead of `start()`?

What is the difference between `Runnable` and `Callable`?

What is the `synchronized` keyword used for?

What is the difference between `synchronized` method and synchronized block?

What is `volatile` in Java?

What is the difference between `wait()`, `sleep()`, and `join()`?

What is the difference between `isAlive()` and `join()`?

What is `Thread.yield()`?

What are the differences between `notify()` and `notifyAll()`?

Why should we avoid using `Thread.stop()`?

What is the difference between `submit()` and `execute()` in ExecutorService?

What is the difference between `synchronized` and `ReentrantLock`?

What is the difference between `ConcurrentHashMap` and `HashMap`?

What is the difference between `notify()` and `notifyAll()`?