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Multithreading Interview Questions in Java


Introduction to Multithreading Interview Questions and Answers in Java

In Java, Multithreading is defined as the process of executing of two or more or multiple threads at the same time. It is used to make the process faster and according to system capacity. It is used to process the smallest units in parallel to achieve the things quickly and make the process faster. It helps in saving memory space and time. It is mainly used for animation, gaming, and large applications.

Now, if you are looking for a job which is related to Multithreading in java then you need to prepare for the 2019 Multithreading Interview Questions in Java. It is true that every interview is different as per the different job profiles. Here, we have prepared the important Multithreading Interview Questions in Java with their Answers to it which will help you get success in your interview.

In this 2019 Multithreading Interview Questions in Java article, we shall present 10 most important and frequently asked Multithreading interview questions in java. These interview questions are divided into two parts are as follows:

Part 1 – Multithreading Interview Questions in Java(Basic)

This first part covers basic Multithreading Interview Questions and Answers in Java.

Q1. Explain the different states of Thread?

The states of the thread are also referred to as Lifecycle of a Thread. The below are the different states of Thread:

  • New: It means the thread is in new state and need to create the instance of thread class before invocation of start method.
  • Runnable: After invoking start method, the thread is in runnable state and scheduler has not selected it to be running thread.
  • Running: When the thread scheduler selected, it is in running state.
  • Blocked: It is also known as Non-Runnable. When the thread is not eligible to run but the thread is still alive.
  • Terminated: This is the state when it exits the run method or in the dead state.

Q2. What is the thread in java?

The thread refers to a small unit which takes less time to get it executed. It mainly independent of the path of execution. It is one of the ways to take advantage of multiple CPU available in the machine. With help of multiple threads, the process of CPU task becomes faster. Java is being majorly used for providing the support to multithreading.

Let us move to the next multithreading Interview Questions in Java.

Q3. Explain the difference between thread and process in JAVA?

The thread is the smallest task of execution within the process. The process is a self-contained execution environment having more than one thread or multiple threads. Threads are the subdivision of process. The thread is having direct access to the data segment of the process whereas the process is having own copy of the data segment. Thread mainly shared the address which is created by the process and process is having their own address. The thread can be easily created and process creation needs a lot of things to do. The thread can easily communicate with other threads whereas process can easily communicate to child process but interprocess communication is difficult. The thread is having its own stack whereas process shares the memory resources like heap memory etc. In the thread, if any change has been done it will affect all the threads but in the process, it does not affect other processes.

Q4. Explain about Java Memory Model?

This is the common multithreading Interview Questions in Java asked in an interview. Several responsibilities normally need to follow by a multithreading tester in current IT industry.

Java Memory model is having a certain set of rules to follow for Java programs to behave in a certain manner across all multiple memory architecture, CPU and operating system which plays an important role in multithreading. Java memory model helps in to distinguish the changes done in one of the thread and that change should be visible to other threads also. In this model, there is a program order rule, which says that each action in thread happens before every action in the thread that comes later in program order.

Q5. Explain the use of Volatile variable in Java Multithreading?

Volatile keyword or variable is used to ensure that shared or instance variables are constantly updated whenever changes made by multiple threads. It is a special modifier that can be used with instance variables only. This keyword cannot be used with methods. If the field in java is declared as volatile, then Java memory model ensures that all threads should have consistent value for that variable. The value of the volatile variable will always read from the main memory. It also reduces the risk of memory consistency errors. Java volatile variable that is an object reference can be null. The volatile keyword needs to be used if the variable is being used across multiple threads.

Part 2 – Multithreading Interview Questions in Java (Advanced)

Let us now have a look at the advanced multithreading Interview Questions and Answers in Java.

Q6. Explain the race condition in threads?

The race condition occurred when there is a race between multiple threads. This race condition is mainly caused due to some programming bugs or errors. The thread which needs to be executed at very first lost the race and then executed the second and some change in the behavior of code that referred as non-deterministic bugs. It becomes one of the difficult bugs to find out and reproduce because of the random nature of threads.

Q7. Explain the fork-join framework in Java?

The fork-join framework is introduced in JDK7. It is a powerful tool for Java developer to take advantage of multiple processors of today’s world servers. It is being mainly designed for work that can be divided into smaller pieces. The main goal is to use the available processing power to raise the application performance. It mainly used the work-stealing algorithm.

Let us move to the next multithreading Interview Questions in Java.

Q8. Explain thread pool and its use in Java?

The pool of thread is known as a thread pool. The thread is generally called as a worker thread. The creation of a thread is costly in many terms like time and resource. When you create the thread at the time of requesting the process, generally it slows down the processor response time and only some limit in a number of threads can be created. So, because of these two major issues, the thread pool has been created. In Java, Java API allows us to create different types of thread pool like a single thread pool, which take only one process at one time. The other is a fixed thread pool that takes a fixed number of threads. Then there is a cached thread pool which is expandable thread pool and mainly suitable for applications for many tasks.

Q9. How the data can be shared between the thread?

This is the most popular multithreading Interview Questions in Java asked in an interview. Some popular test cases in the current IT industry.

The data can be shared between threads with help of using the shared object or concurrent data structure like Blocking queue. It mainly follows the producer-consumer pattern using wait and notifies methods that involve sharing object between the two threads.

Q10. How threads distributed in stack and heap memory?

In Java, each thread has its own stack which is used to store local variables, method parameter, and call stack. Heap memory is common memory which is being shared by all the threads.

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This has been a guide to the list of Multithreading Interview Questions and Answers in java so that the candidate can crackdown these Multithreading Interview Questions in Java easily. Here in this post, we have studied top Multithreading Interview Questions in Java which are often asked in interviews. You may also look at the following articles to learn more –

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Multithreading Interview Questions in Java


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