5 Java Concurrency Interview Questions (Answers And Tips)

Updated 2 March 2023

Java concurrency is a feature of Java that allows developers or programmers to run multiple programs in parallel and ensure high performance. During a software developer or programmer interview, hiring managers may ask technical and in-depth questions to evaluate your knowledge of Java concurrency. Reviewing such questions and learning how to answer them can help you increase your chances of securing a job. In this article, we discuss a list of Java concurrency interview questions along with sample answers and provide tips to help you prepare for your interview.

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Java Concurrency Interview Questions With Sample Answers

Here are some Java concurrency interview questions with example answers you can use as a guide when creating your own:

1. What is the difference between a thread and a process?

Interviewers may ask this question to analyse your basic computer science knowledge. Threads and processes are independent execution sequences that may relate to each other. While answering this question, focus on responding in a clear, concise and factual way.

Example answer: A thread is a lightweight unit of execution within the process. The process itself is a heavyweight unit of execution with its own space and system resources memory. Threads and processes are alike in that they are both independent execution sequences. In simple terms, a thread is a segment of a process, and a process is a program undergoing execution. Executing a thread often requires fewer resources than executing a process.

2. Can you describe multithreading and its uses?

This question can help interviewers test your basic knowledge and understanding of multithreading and its benefits. In your answer, explain how to use multithreading to improve the performance of Java applications. Consider highlighting examples where you used this method in your previous work.

Example: You can create multithreading in Java by using the thread class and companion interface, with its message and runnable. It is possible to understand multithreading by using a Java virtual machine to allow the execution of multiple threads concurrently. There are various benefits of multithreading in Java concurrency, including improving an application's performance and responsiveness. It is also helpful for utilising multiple CPU cores, reducing idle time and performing multiple tasks simultaneously.

3. What do you know about race conditions in multithreading?

Hiring managers may ask this question to determine if you are aware of race conditions and their characteristics. A race condition in multithreading is a situation where multiple threads access and modify the same shared resource. While answering this question, consider keeping your response informative and to the point. You may also elaborate on race conditions with the help of examples.

Example answer: Race conditions in multithreading are concurrency bugs that occur because the program operates with parallel execution, using multiple threads simultaneously. The risk of race conditions is higher in Java because it is a multi-threading programming language. To prevent race conditions from occurring, it is helpful to locate their root cause. An example of race conditions can be banking transactions, where two threads are trying to withdraw money from the same account simultaneously.

4. What is synchronisation in Java and how can you achieve it?

This question can help interviewers assess your knowledge of this topic. Synchronisation in Java is a process that can help control multiple thread access to shared resources. While answering, consider highlighting your experience with synchronisation in Java and its applications.

Example answer: Synchronisation is a process or mechanism in Java that ensures only one thread at a time is responsible for executing key sections of code. You can achieve synchronisation in Java by applying a synchronised keyword to a block of code. You can also use the java.util.concurrent.locks package. This results in providing synchronisation mechanisms that are more advanced.

5. What do you know about interthread communication?

During your interview, you can expect questions, such as this, that probe your knowledge and skills as a software developer. Interthread communication helps synchronised threads communicate with each other. While answering this question, explain the meaning of interthread communication in Java and how it can be useful.

Example answer: Interthread communication in Java refers to the mechanism in which threads synchronise and communicate with each other. This process is useful for pausing a running thread to allow another thread to enter the same section. There are various methods for achieving interthread communication in Java, including “wait()”, “notify()” and “join()”, synchronised keyword, volatile keyword and java.util.concurrent package.

Tips For Preparing For A Java Concurrency Interview

During an interview, hiring managers may ask questions to assess your fluency with Java concurrency. When responding, focus on providing answers that are factual and example based. You may highlight how your experience helps you solve issues and find the best solutions. Here are some tips to help you prepare for a Java concurrency interview:

Understand the basics of Java concurrency and multithreading

Professional developers often use concurrency and multithreading in Java to provide improved user experience and responsiveness. That is why interviewers may ask you questions that relate to concurrency and threading, including their characteristics and use in Java applications. To improve your knowledge and help differentiate you from other candidates, pursue relevant courses to enhance your concurrency and multithreading skills. Here are several online certifications that you can pursue:

Parallel programming in Java
Concurrent programming in Java
Distributed programming in Java

Learn more about java.util.concurrent package

As many Java developers use this package for building concurrent Java applications, interviewers may ask about this mechanism's components or utilities. Having a sound knowledge of java.util.concurrent can be helpful when applying for a Java developer role. It is also useful to know about the package's ability to provide classes that support the scheduling of tasks and thread-safe queue implementation.

Practice mock interviews

Taking part in mock interviews can be a great way to prepare your answers in advance. It can also teach you the right way to deliver your responses and highlight areas that require improvement. Getting feedback on your mock interview performance can also help identify areas to work on. Ask a family member or trusted colleague to conduct mock interviews with you and prepare concepts and techniques that relate to Java concurrency.

Improve your technical skills

During an interview, hiring managers may ask you about atomic operations, synchronisation, threads, java.util.concurrent package, thread safety or types of locks. It is helpful to study the basic concepts, benefits and methods for these specific areas. You can also practice solving issues that relate to concurrency and multithreading. This may help you improve your technical skills and gain a better understanding of Java concurrency.

Research the job description and the company

Studying the job description for the position you are applying for can help you gain important insights into the post and company. A job description often contains the necessary skills and qualifications for the role. Consider researching the company to learn about the products or services they offer. It is also helpful to explore the technology the company works with and the projects they handle. This may give you an idea of the issues they face during a concurrency project. In an interview, you can then explain how your experience and knowledge can help in fixing these concurrency-related issues.