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Home / Interview Subjects / Java Multithreading
WithoutBook LIVE Mock Interviews Java Multithreading Related interview subjects: 39

Interview Questions and Answers

Know the top Java Multithreading interview questions and answers for freshers and experienced candidates to prepare for job interviews.

Total 30 questions Interview Questions and Answers

The Best LIVE Mock Interview - You should go through before interview

Know the top Java Multithreading interview questions and answers for freshers and experienced candidates to prepare for job interviews.

Interview Questions and Answers

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Experienced / Expert level questions & answers

Ques 1

What is deadlock in multithreading?

Deadlock is a situation where two or more threads are blocked forever, waiting for each other to release the locks.

Example:

Thread 1 locks resource A and waits for resource B. Thread 2 locks resource B and waits for resource A.
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Ques 2

Explain the concept of the wait-notify mechanism.

The wait-notify mechanism is used for inter-thread communication, where one thread can signal the other that a certain condition has been met.

Example:

Using wait(), notify(), and notifyAll() methods in synchronized blocks.
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Ques 3

How does the join() method work in Java?

The join() method is used to wait for a thread to die. It causes the current thread to pause execution until the specified thread completes its execution.

Example:

Thread anotherThread = new Thread(() -> { 
/* Thread logic */ }); 
anotherThread.start(); 
anotherThread.join();
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Ques 4

Explain the concept of a race condition.

A race condition occurs when two or more threads access shared data concurrently, and the final outcome depends on the order of execution.

Example:

When two threads increment a shared counter without proper synchronization.
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Ques 5

What is the ReentrantLock class in Java?

The ReentrantLock class is a part of the java.util.concurrent package and provides a flexible locking mechanism with the ability to interrupt a thread that is waiting for the lock.

Example:

ReentrantLock lock = new ReentrantLock(); 
lock.lock(); 
try { /* Critical section */ } 
finally { lock.unlock(); }
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Ques 6

Explain the concept of the producer-consumer problem in multithreading.

The producer-consumer problem involves two types of threads: producers that produce data and consumers that consume the data. The challenge is to synchronize their activities.

Example:

Using a shared buffer and synchronization mechanisms to ensure proper communication between producers and consumers.
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Ques 7

Explain the concept of thread dumping.

Thread dumping involves generating a snapshot of all the threads' current state and stack traces. It is useful for diagnosing performance or deadlock issues.

Example:

In Java, you can use tools like jstack or VisualVM to generate thread dumps.
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Ques 8

Explain the concept of the happens-before relationship in Java.

The happens-before relationship is a partial ordering of memory operations in Java. It ensures that the result of one operation is visible to another, providing a consistent view of shared data among threads.

Example:

Using synchronized blocks establishes a happens-before relationship.
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Ques 9

What is the purpose of the Phaser class in Java?

The Phaser class in Java provides a more flexible alternative to the CountDownLatch and CyclicBarrier for synchronizing threads. It supports dynamic registration of threads and phase advancement.

Example:

Phaser phaser = new Phaser(); 
phaser.register(); // Register the current thread
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Ques 10

What is the purpose of the Exchanger class in Java?

The Exchanger class provides a synchronization point at which threads can pair and swap elements within pairs. Each thread presents some object on entry to the exchange method, matches with a partner thread, and receives its partner's object on return.

Example:

Exchanger exchanger = new Exchanger<>();
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Ques 11

Explain the concept of the ForkJoinPool in Java.

The ForkJoinPool is a special-purpose ExecutorService designed for parallelizing divide-and-conquer algorithms. It is particularly useful for recursive tasks with multiple subtasks.

Example:

RecursiveTask and RecursiveAction are classes commonly used with ForkJoinPool.
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