Top 25 Java Interview Questions and Answers in 2021

By Nandini

Last updated on Nov 15 2021

Top 25 Java Interview Questions and Answers in 2021

Top 25 Java Interview Questions and Answers in 2021


Introduction to Java


Java is the most widely used and deployed language in the world. Created by James Gosling, Patrick Naughton and Mike Sheridan in 1991 while they were working with Netscape Communications, Java is now one of the three core technologies in the world of web. Being the high-level language, Java has made its mark in the IT industry with its first-class functions and holds a bright future.


Why is Java important?


In Java, the primary advantage is that it eliminates the need for recompilation. It enables developers to write code that runs everywhere making it easier and feasible for them to perform their tasks.

Regardless of the architecture of a system, Java compiled code can run on any JVM (Java virtual machine). This makes it one of the foremost widely-used programming languages. Java is a class-based and object-oriented programming language.

If you are aspiring to acquire this skill and make a career as a Java developer, you must consider taking up the Java course training from a reputed training provider and get certified.

Here, in this Java Interview Questions article, we have listed out the most important Java Interview Questions and Answers which will prepare you for any Java interview process.

For professionals with good knowledge of Java programming, looking for job opportunities and interviews, we have something interesting for you.

Here’s an updated list of top Java interview questions and answers that’ll help you in Java interviews.


Java Interview Questions and Answers – Set 1:


  1. Define class in Java?


In Java, a class is a template used to create objects and define the data type of them. It acts as a building block for Java language-oriented system.


  1. Explain the difference between dynamic and static loading?


Static class loading involves the creation of objects and instances using new keywords and dynamic class loading is done when the name of the class is not known at compile time.


  1. What is multi-threading?


It is a programming concept that allows to run multiple tasks within one single program in a concurrent manner.


  1. When and by whom was Java developed?


Java was developed in 1995 by James Gosling.


Java Interview Questions and Answers – Set 2:


  1. What do JVM, JRE, and JDK stand for?


  • JVM stands for Java Virtual Machine.
  • JRE stands for Java Runtime Environment.
  • JDK stands for Java Development Kit


  1. Does Java use pointers?


No, Java doesn’t use pointers. It has tough security. Instead of pointers, references are used in Java as they are safer and secure when compared to a pointer.


  1. Explain the steps involved in connecting to a database in java?


Below are the steps to connect to a database in Java,

  • Registering the driver class
  • Creating connection
  • Creating statement
  • Executing queries
  • Closing connection


  1. Explain the functions of JVM and JRE?


The function of JVM is to offer a runtime environment for Java Byte Codes to be executed. And JRE includes the sets of files required by JVM during its runtime.


  1. Explain the difference between overloading and overriding?


Overloading occurs when there are two methods of the same name but different properties.

When there are two methods of the same name and properties, one is in the child class and the other is in the parent class, overriding occurs.


Java Interview Questions and Answers – Set 3:


  1. What is the default size of load factor in hashing based collection?


The default size is 0.75 and the default capacity is computed as


Initial capacity * Load factor.



  1. What is a package?


A Package is a collection of related classes and interfaces.


  1. What is the superclass of all exception classes?

Java.lang.Throwable is the superclass of all exception classes. In Java, all exception classes are derived from this base class.


  1. Explain the difference between equals() and = =?

Equals() method is used for checking equality of two objects defined by business logic.

“==” aka the equality operator is used to compare objects and primitives.



  1. State two differences between inner class and subclass

Inner classes must be in the same file whereas the subclasses can be in different files.

And subclasses have the methods of their parent class, but the inner classes can get the methods they want.


Java Interview Questions and Answers – Set 4:


  1. How are destructors defined in Java?

Java has its own garbage collection. This means that no destructors are required to be defined in Java. Destruction of objects is an automated process that is performed by the garbage collection mechanism.


  1. Define JSON

JSON is an acronym for JavaScript Object Notation. It uses the JavaScript syntax. The format in JSON is text only.


  1. What is the most important feature of Java?

The most important feature of Java is that it is a platform-independent language.


  1. What is an anonymous class?

The class that is defined in a single line of code using new keyword and without a name is an anonymous class.


  1. What is a JVM?

JVM is a Java Virtual Machine which is a runtime environment for the compiled java class files.


Java Interview Questions and Answers – Set 5:


  1. Can a dead thread be started again?

 No, a thread that is in the dead state can't be started again.


  1. Are arrays of primitive data types?

No. In Java, Arrays are objects.


  1. What are constructors in Java?

      In Java, the constructor is a block of code which is used to initialize an object.


  1. What are the types of constructors?

There are two types of constructors:

  1. Default constructor
  2. Parameterized constructor


  1. Explain garbage collection in Java

In Java, when an object is longer used or referenced, garbage collection is called and the object is destroyed automatically.


  1. What's the difference between Stack and Queue?

 The difference between a stack and a queue is that stack is based on Last in First out (LIFO) principle and a queue is based on FIFO (First In First Out) principle.


Java Interview Tips


Having discussed the list of important Java Interview Questions and Answers, here we have listed some quick basic interview tips to help you ace the Java interview,

  • Be punctual and show up on time.
  • Be confident and communicate effectively
  • Avoid using slang words and fillers.
  • Read the job description and research about the company.
  • Listen carefully and take time before answering. Make sure your answers are relevant to the questions asked.
  • Dress and behave professionally.
  • Avoid interrupting the interviewer.
  • Carry all the essential documents.
  • Understand the job requirements and explain how you can fulfill them.
  • Thank the interviewer for his/her time. Ask for feedback and be open to constructive criticism too.


If you want to learn Java online, you can sign up for the course on Sprintzeal’s E-learning platform and take up their Java online course to get certified.




JavaScript is a vast topic. The list of Java interview questions and answers could be endless. But we hope you’ve found this comprehensive list of Java interview questions and answers we made for you informative and helpful.

To ensure you are well versed with all the Java programming related concepts, you can take up Java training and add the certification to your resume. Sprintzeal is a global training provider offering a wide range of training and certifications for professionals. You can get an overview and practical knowledge of Java concepts with our Java certification training. You get trained by our industry expert and accredited trainers. And the skills acquired from our Java training will give you an edge over other candidates when you attend interviews.

For more Java training and certification related details, you can reach us at Click Here or chat with our course expert. If you’re looking for other training and certifications to enhance your career, you can explore all courses offered by us and request for a trial.

If you are encountering any difficulties with these java interview questions, feel free to reach us. Besides this Java Interview Questions Blog, if you want to gain more knowledge about the programming language, you can get in touch with our trainers and opt for the Java training program.

So this leads us to the end of the blog for Java interview questions. The questions you were exposed to in this Java Interview Questions blog remain the most commonly asked questions by the recruiters in the industry. We are certain that these sets of Java Interview Questions will be of great help to you if you are preparing for interviews.

If you'd like to read the extended version of this Java interview questions and answers blog which involves OOPs interview questions and Spring interview questions, be sure to check our blog regularly or subscribe to our newsletter.


Recommended Article: Top 25 ITIL Interview Questions and Answers in 2020





About the Author

Sprintzeal   Nandini

With over 3 years of experience in creating informative, authentic, and engaging content, Nandini is a technology content writer who is skilled in writing well-researched articles, blog posts, newsletters, and other forms of content. Her works are focused on the latest updates in E-learning, professional training and certification, and other important fields in the education domain.

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