Top 40+ Multithreading interview questions

In this tutorial, we will look into some of the most commonly asked Multithreading interview questions.

To learn about Multithreading, you can check here.

Multithreading interview questions in java

1. What is Concurrency in java?
   • This is one of the most commonly asked Multithreading interview questions in java, Concurrency refers to the ability to carry out multiple tasks simultaneously. In Java, concurrency refers to the program’s ability to run multiple threads or processes concurrently; threads are lightweight processes that share memory space while running at the same time – this ability makes Java an incredibly powerful programming language.
2. Why we need multithreading?
   • Multithreading is a technique used to improve the performance of a program by allowing it to execute multiple tasks simultaneously. This technique is especially useful in situations where the program needs to perform multiple tasks at the same time, such as in server applications, where multiple clients may be accessing the same resources simultaneously.
   • By using multithreading, a program can utilize the available resources efficiently and reduce the time taken to complete the tasks. This not only improves the performance of the program but also enhances the user experience by reducing the response time.
   • In summary, we need multithreading to improve the performance of a program and utilize the available resources efficiently. It is a powerful technique that allows a program to execute multiple tasks simultaneously and reduce the time taken to complete the tasks.
3. Explain the Advantages we get with multithreading.
   • This is one of the most commonly asked Multithreading interview questions in java, Multithreading is an efficient method that offers numerous advantages over single-threaded programs. Multithreading benefits may include:
   • Increased Performance: Multithreading can greatly enhance a program’s performance by allowing it to execute multiple tasks at the same time, effectively using available resources while shortening completion times of tasks.
   • Multithreading Increases Responsiveness: Multithreading can significantly enhance a program’s responsiveness by enabling it to respond more rapidly to user input while performing other tasks in the background, thus improving user experience and decreasing perceived response times.
   • Resource Sharing: Multithreading can enable multiple threads to share resources such as memory and CPU more efficiently, thus decreasing resource use while increasing program scalability.
   • Modular Design: Multithreading allows a program to be designed modularly, with each thread performing its own specific function – making the code simpler to comprehend and maintain.
   • Multithreading provides programs with an option for performing asynchronous processing, in which one thread continues processing while waiting for input/output operations to complete; this can increase efficiency overall and boost program effectiveness.
4. Explain the Disadvantages with multithreading.
   • Complex Programming: Multithreading adds complexity to programming a program, necessitating careful coordination among threads, synchronization of data and management of shared resources – which can be challenging and error-prone tasks.
   • Race Conditions: Multithreading can create race conditions, in which multiple threads accessing and updating a resource simultaneously create unpredictable behavior and data corruption.
   • Deadlocks: Multithreading can lead to deadlocks, where two or more threads are waiting on each other for resources that must be released before proceeding with their task – potentially freezing up your program and leading to its shutdown.
   • Increased Overhead: Multithreading can add unnecessary overhead to a program, including thread synchronization and communication between threads; this can reduce performance overall.
   • Debugging and Testing: Debugging multithreaded programs is often difficult due to race conditions or deadlocks preventing reproduction and isolation of issues.
5. What are the different ways to create a thread?
   • This is one of the most commonly asked Multithreading interview questions in java, Extension of the Thread Class: Extending the Thread class involves creating a subclass and overriding its run() method with code that will execute when starting a thread. When starting up this new thread, its subclass needs to be instantiated and its start() method must be called upon for activation.
   • Implementing the Runnable interface: To implement this interface, one needs to create a class which implements it, providing an implementation for its run() method and then instantiating that class as an argument to a Thread constructor, then calling its start() method on that thread object in order to start it running.
   • Both methods for creating threads offer their own set of advantages and disadvantages. Extending the Thread class gives more control over its behavior by giving access to methods like getName(), setPriority() and interrupt(); however, this may cause inheritance problems as an object subclassed from Thread cannot inherit from any other class. Checkout code here.
   • Implementing the Runnable interface provides greater flexibility, as classes that implement this interface may also implement other interfaces or inherit from a superclass. However, doing so requires an additional object be created and passed as an argument to Thread constructor.
   • For more please refer to our thread tutorial
6. What is deadlock in java?
7. How to resolve deadlock in java?
8. Write a code to generate deadlock in java.
9. What is race condition in java ?
10. Difference between calling wait() and sleep() method.
11. Explain Thread pooling in multithreading.
12. What is synchronization in java?
13. Explain shutdown hook in multithreading.
14. Explain context switching in java.
15. What is Blocking Queue in java ?
16. Difference between synchronized method and synchronized block
17. What is volatile in java ?
18. How to stop a thread in java?
19. What is Blocking Queue?
20. Explain Thread Local in java ?
21. What is producer, consumer problem in java?
22. Explain how threads communicates with each other.
23. Difference between Cyclic Barrier and Countdown Latch?
24. What is ReentrantLock in java ?
25. What is read write lock ? Explain its benefits.
26. Difference between Thread and process in java.
27. When to use Runnable vs Thread ?
28. Difference between run() and start() method.
29. Difference between Runnable and callable in java?
30. What is volatile in java?
31. What happens when an exception occurs in thread ?
32. How do you check if a thread holds a lock or not ?
33. What is executor framework in java?
34. What is the difference between invokeAndWait and invokeLater in java?
35. How do you take thread dump in java ?
36. What is busy spin in multithreading?
37. What is fork-join framework in java ?
38. Difference between process and thread
39. What are the advantages of executor service in java
40. What is Completable in java?
41. How do you create a completable future in java?
42. What is asynchronous communication in java ?
43. Can you explain what “Completion Stage” means in the context of CompletableFuture?
44. What is blocking and non-blocking calls ?
45. What is the use of isDone() method in CompletableFuture.
46. Can you explain the difference between supplyAsync() and runAsync() ?