Top 75 java multithreading important interview questions in 2023

Java multithreading important interview questions and answers: Multiple threads can execute simultaneously thanks to multithreading, a fundamental Java feature. A thread is simply a sub-process, often consisting of a block of code that carries out a single task. Interviews for software engineering positions such as front-end, back-end, and full-stack developers usually include questions about Java Multithreading. These Java Multithreading interview questions will offer you a decent idea of what to expect during your interview if Java is your favorite programming language.

Top 75 java multithreading important interview questions for beginners and experienced in 2023

You will undoubtedly encounter a few questions about threads, concurrency, and multi-threading in any Java interview, whether you are a fresher, junior developer or an experienced professionals.  In actuality, the Java programming language’s built-in concurrency support is one of its finest features and contributed to both programmers and the business world’s acceptance of the language. Excellent fundamental Java multi-threading skills and experience in creating, debugging, and tweaking high-performance, low latency concurrent Java applications are requirements for the majority of lucrative Java developer positions. It is one of the most crucial subjects in Java interviews for this reason. The concepts of concurrency and multithreading are difficult to understand, and only competent programmers with extensive expertise can successfully handle concurrency problems.

Top 75 Java Multithreading Interview Questions and Answers

How do threads work in java ?

The lowest and lightest processing unit that a scheduler can control independently is a thread. Threads are components of a process that only enable the concurrent, efficient execution of programs with other components or threads of the process. The simplest approach to complete challenging tasks is by using threads. It is thought to be the simplest method for utilizing a machine’s numerous CPUs. They are separate from one another yet share the same address space.

Define a process in java ?

What is a Process ? : A process is merely refers to an active programs, or one that is now running.  A process can have multiple threads by dividing the problems into smaller modules for execution.

Computer operating systems employ a data structure known as a process control block (PCB), commonly referred to as a process descriptor, to hold all the details about a process.

The operating system constructs a corresponding process control block when a process is created (initialized or installed), which specifies and tracks the process status (i.e., new, ready, running, waiting, or terminated). The PCB is essential for context switching because it tracks process information.

What distinguishes a Java process from a thread ?

Thread and process are related to each other but still a thread working is different from the process. The below given are the common differences or high level comparisons between a thread and a process which makes them different from each other.

What advantages are provided by multithreading in java ?

Java threads can provide the below given advantages in the application programming: 

  • Better performance compared to multi-process, typical parallel programs.
  • Enables the creation of efficient applications that make the most of CPU time.
  • Enhances the responsiveness of sophisticated programs or applications.
  • Utilize CPU resources more efficiently and spend less on maintenance.
  • Reduces workload and parallelism.
  • Threads are independent, therefore if an exception arises in one thread, it won’t effect any other threads.
  • Threads are less resource-intensive in comparison to running several processes simultaneously

What are the possible ways in java to implement threads ?

  • A Java class extending the Thread class
  • A Java class implementing the runnable interface 

Read the below given blog link to understand in detail about implementing threads in java 

Explain the thread implementation in java ?

Describe the Java daemon thread in java ?

The daemon threads, which have a low priority, give the user threads assistance and services in the background. If the program only uses the daemon thread and all other user threads are terminated or killed, the daemon thread is immediately stopped by the JVM.

The below given are the methods for daemon thread available in the Thread class:

  • public void setDaemon(boolean status): It used to mark the thread daemon thread or a user thread.
  • public boolean isDaemon(): It checks the thread is daemon or not.

Explain the main differences between a Java Thread and Runnable Interface in Java?

Difference between thread and runnable interface in java ?

Mention few differences between a daemon thread and a user thread in java ?

Differences between a daemon thread and user thread in java

Differences between a thread and a process in java ?

Differences between a thread and a process in java

What is the main difference between start() and run() in java threads ?

Difference between start() and run() method in java threads

Explain thread pool in java ?

A thread pool is a collection of worker threads or pre-initialized threads at startup that can be used to carry out tasks and returned to the pool once finished. The process of creating a collection of fixed-size threads is known as creating a pool of threads. Using a thread pool, one may manage the lifecycle of application threads while minimizing the number of threads in use. Performance can be improved, and system stability can be improved, by using threads.

The java.util.concurrent.Executors class often includes factory methods to generate the thread pools.

Explain the role of join() method in java threads ?

The join() method is typically used to suspend a thread’s progress until and unless the thread on which join is called is dead or finished. This approach can be used to halt one thread from continuing while another is being terminated. It connects the beginning of one thread’s execution to the conclusion of another thread. It is regarded as a thread class’s final procedure.

  • public void join()throws InterruptedException
  • public void join(long milliseconds)throws InterruptedException

What do you mean by Garbage Collection in java ?

In essence, garbage collection is an autonomous memory management system. It employs a number of GC algorithms, with Mark and Sweep being two of the more well-known ones. There are three stages to the process: marking, deleting, and compaction/copying. To put it simply, a garbage collector identifies items that are no longer needed by the application and removes or deletes them to free up memory.

Explain the role of volatile variable in multithreaded java programming?

In multithreaded programming, a volatile variable is essentially a keyword that is used to guarantee and address the visibility of changes to variables. The volatile keyword can be used with variables but not with classes or methods. It serves only as a means of achieving thread safety. If a variable is marked as volatile, all threads can access its value directly from main memory rather than the CPU cache, allowing each thread to obtain the variable’s most recent value.

Which methods can be used for thread communication in java ?

There are 3 thread methods used for thread communication. 

  • wait() 
  • notify() 
  • notifyAll () 

Explain the role of finalize() method in java ?

Basically, the Finalize() method of the Object class is a method designed for cleaning up unmanaged resources immediately before garbage collection. It is in no way meant to be referred to as a standard procedure. When the finalize() method has finished running, the object is automatically deleted.

what is synchronization in java ?

In Java, synchronization essentially allows a straightforward method for preventing thread interference and memory consistency problems. When one thread wants to access a shared resource, this procedure ensures that only one thread will be using it at a time. 

Thread synchronization could be of 2 types : Mutual Exclusive and inter-thread communication.

  1. Mutual Exclusive
    1. by implementing  synchronized method in java class 
    2. by implementing synchronized block in java class
    3. by implementing static synchronization  in java class
  2. Cooperation (Inter-thread communication in java)

How the java objects can be locked for exclusive use by threads ?

 The java objects can be locked by using the  “synchronized” block. The locked object becomes exclusive to the thread and cannot be invoked by other threads unless the current thread holding the lock is in execution. 

Provide the difference between notify() and notifyAll() thread method in java ?

One waiting thread can be unblocked using the notify() method, but all waiting threads can be unblocked using the notifyAll() method.

Explain thread scheduler in java ?

A Thread Scheduler, a component of the JVM, is used to supervise threads when they are created in Java. Only choosing which thread should be executed is up to the thread scheduler. Preemptive and Time Slicing are the two scheduling methods used by the thread scheduler.

The Java thread scheduler can also choose amongst the following options for a thread:

  • Thread Scheduler chooses the thread’s priority.
  • Thread Scheduler establishes how long a thread will wait.
  • Thread Schedule examines the thread’s nature.

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