Introduction to Multithreading Interview Questions and Answers in Java
In Java, Multithreading is defined as the process of executing 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 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 related to Multithreading in java, you need to prepare for the 2021 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, which will help you get success in your interview.
In this 2021 Multithreading Interview Questions in Java article, we shall present the 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 Interview Questions and Answers in Java.
Q1. Explain the different states of Thread?
The states of the thread are also referred to as the Lifecycle of a Thread. Below are the different states of Thread:
- New: It means the thread is in a new state and needs to create the instance of thread class before the invocation of the start method.
- Runnable: After invoking the start method, the thread is in a runnable state, and the scheduler has not selected it to be a running thread.
- Running: When the thread scheduler is selected, it is in a 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 is in the dead state.
Q2. What is the thread in java?
The thread refers to a small unit that takes less time to get executed. It is mainly independent of the path of execution. It is one of the ways to take advantage of multiple CPUs available in the machine. With the help of multiple threads, the process of the CPU task becomes faster. Java is majorly used for providing support to multithreading.
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 the 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 the process has its 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 the process can easily communicate to the child process, but interprocess communication is difficult. The thread is having its own stack, whereas the process shares the memory resources like heap memory etc. If any change has been done in the thread, it will affect all the threads, but in the process, it does not affect other processes.
Q4. Explain about Java Memory Model?
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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. The Java memory model helps to distinguish the changes done in one of the threads, and that change should also be visible to other threads. This mod is a program order that says that each thread’s action happens before every thread comes later in the program order.
Q5. Explain the use of Volatile variables in Java Multithreading?
A volatile keyword or variable is used to ensure that shared or instance variables are constantly updated whenever changes are 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 the Java memory model ensures that all threads should have consistent value for that variable. The value of the volatile variable will always be 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 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 that needs to be executed initially lost the race and then executed the second and some change in the behavior of code that referred to 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 developers to take advantage of multiple processors of today’s world servers. It is mainly designed for work that can be divided into smaller pieces. The main goal is to use the available processing power to raise application performance. It mainly used the work-stealing algorithm.
Q8. Explain the 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, as time and resources. 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 the 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, an expandable thread pool and mainly suitable for many tasks.
Q9. How can the data be shared between the thread?
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The data can be shared between threads with the help of using the shared object or concurrent data structure like a Blocking queue. It mainly follows the producer-consumer pattern using wait and notifies methods that involve sharing an object between the two threads.
Q10. How are threads distributed in stack and heap memory?
In Java, each thread has its own stack, which is used to store local variables, method parameters, and call stack. Heap memory is a common memory that is being shared by all the threads.
This has been a guide to the list of Multithreading Interview Questions and Answers in java so that the candidate can crackdown these 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 –