Most Commonly Asked Core Java Interview Questions

Core Java is an integral part of the Java programming language widely used for developing general-purpose applications. Considering its versatility and ease of use, Core Java is the first choice for any app developer worldwide. Leading tech companies across the globe now implement Core Java in their software development projects. Likewise, FAANG and Tier-1 tech companies look for individuals adept in Core Java while hiring. To crack such a tech interview, you need to prepare for the commonly asked Core Java interview questions in advance.

If you are preparing for a tech interview, check out our technical interview checklist, interview questions page, and salary negotiation ebook to get interview-ready!

Having trained over 9,000 software engineers, we know what it takes to crack the most challenging tech interviews. Since 2014, Interview Kickstart alums have landed lucrative offers from FAANG and Tier-1 tech companies, with an average salary hike of 49%. The highest ever offer received by an IK alum is a whopping $933,000!

At IK, you get the unique opportunity to learn from expert instructors who are hiring managers and tech leads at Google, Facebook, Apple, and other top Silicon Valley tech companies.

Want to nail your next tech interview? Sign up for our FREE Webinar.

Now, let’s look at the most common Core Java questions asked in interviews. Here’s what we’ll cover:

• Popular Concepts of Core Java
• Core Java Interview Questions for Beginners
• Core Java Interview Questions for Intermediates
• Advanced Core Java Interview Questions for Experts
• Frequently Asked Core Java Interview Questions
• Core Java FAQs

Popular Concepts of Core Java

These are some of the prominent basic Java concepts that a beginner should know:

• Java Fundamentals and basic Java constructs like loops and data types
• OOPS concepts (Data Abstraction, Encapsulation, Inheritance, Polymorphism)
• Overloading & Overriding
• Collection framework
• String handling
• Multithreading
• Packages
• Exception handling
• Swings
• Generics
• Synchronization
• Serialisation & De-serialisation
• Applets
• Concurrent collection
• JDBC (Basic Database Connections)

To brush up on your Java fundamentals, visit the Learn folder and check out our comprehensive articles on Java.

Core Java Interview Questions for Beginners

If you are a beginner trying to start your career with Core Java, go through the sample interview questions listed below.

1. What are the contents of a Java download file?
2. Explain JDK.
3. What is JRE?
4. State the differences between JDK and JRE.
5. Define ClassLoader.
6. What are the types of Memory Allocations in Java?
7. Can a program run if static public void main is included?
8. What value does Local Variables store by default?
9. Explain Copy Constructor in Java.
10. Define Marker Interface.
11. What do you know about Object Cloning?
12. Explain why Java is not a 100% object-oriented programming language.
13. What are Wrapper Classes?
14. What are Singleton Classes?
15. Explain package in Java.
16. Are there pointers in Java?
17. What are the differences between instance and local variables?
18. What do you know about the Java String Pool?
19. Define Exception in Java.
20. What is the purpose of final in Java?
21. What happens if the main() is not declared as static?
22. Explain the features of Java.
23. How is high performance enabled in Java?
24. What are the IDEs of Java?
25. Define Class in Java.
26. Explain an Object in Java.
27. What are the concepts behind OOP?
28. Define Inheritance in Java.
29. Explain Encapsulation.
30. Why is Encapsulation used in Java?

Core Java Interview Questions for Intermediates

In this section, you will find some frequently asked Core Java interview questions for intermediate-level software developers and engineers.

1. What are the variants of JDK?
2. Explain Access Specifiers in Java.
3. What are the types of Access Specifiers?
4. Does a constructor return a value in Java?
5. What is the ‘this’ keyword in Java?
6. Why is the ‘super’ keyword used in Java?
7. What is Method Overloading?
8. Is it possible to overload a static method?
9. What is Late Binding in Java?
10. Explain Dynamic Method Dispatch in Java.
11. Why does the delete function work faster in the linked list than in an array?
12. What do you know about the life cycle of a thread?
13. Difference between >>> and >> operators.
14. What can you tell about the life cycle of an applet?
15. Why do we use generics in Java?
16. What do you know about the Externalizable interface?
17. Explain Daemon Thread in Java.
18. What is enumeration in Java?
19. Why is Java dynamic?
20. Is it possible to run a code before the execution of the main method?
21. How often is the “finalize” method called in Java?
22. Define Polymorphism in Java.
23. What is Overloading in Java?
24. Explain Abstract class.
25. Differentiate between Array and Array List.
26. Differentiate between String, String Buffer, and StringBuilder.
27. What are Public and Private access specifiers?
28. What are the differences between Protected and Default access specifiers?
29. State the difference between HashMap and HashTable.

Advanced Core Java Interview Questions for Experts

Some advanced Core Java interview questions for experienced professionals are listed below:

1. Can you use “this” and “super” keywords together in Java?
2. Explain a JSP page.
3. What do you know about JDBC?
4. Define observer and observable classes in Java.
5. Explain Session Management in Java.
6. What do you know about Spring Framework?
7. Explain JCA in Java.
8. What is JPA in Java?
9. What are the various authentications in Java Servlets?
10. Define FailFast iterator.
11. What is FailSafe iterator?
12. How can you reverse a string in Java?
13. Write a program in Java to find the square root of a number.
14. Write a program to detect duplicate characters in a string.
15. Differentiate between System.out, System.err, and System.in.
16. Implement a Dictionary in Java having a large number of words.
17. Write a pattern program in Java.
18. What are the differences between Abstract class and Interface?
19. Define Collections in Java.
20. What are the Classes and Interfaces available in Collections?
21. Explain Ordered and Sorted in Collections?
22. What are the different lists available in the Collections?
23. What do you know about Set in Collections?
24. Explain the types of Sets in Java.
25. What is a Map in Java?
26. What are the types of Maps in Java?
27. Define Priority Queue.
28. What are the different types of Exceptions in Java?
29. Explain the different ways to handle exceptions.

Frequently Asked Core Java Interview Questions

In this section, you will find some bonus miscellaneous Core Java interview questions.

1. Explain the advantages of Exception handling in Java.
2. Define the Exception handling keywords.
3. What do you know about Exception Propagation?
4. How can you make a thread in Java?
5. What do you know about the join() method?
6. What is the purpose of the yield method of the Thread class?
7. Explain wait() method.
8. Differentiate between notify() and notifyAll() methods in Java.
9. How can you stop a thread in Java?
10. Explain sleep() method in a thread.
11. When can you use the Runnable interface in Java?
12. When should you use the Thread class in Java?
13. Differentiate between run() and start() method of thread class.
14. Define Multithreading in Java.
15. Explain Synchronization.
16. What do you know about the disadvantages of Synchronization?
17. Define Serialization in Java.
18. Why do we use a transient variable in Java?
19. Differentiate between Serializable and Cloneable.
20. What are the methods used during Serialization and Deserialization processes?
21. What is the function of a Volatile Variable in Java?

Need more practice questions? Read Top Java Interview Questions for a comprehensive list of Java interview questions asked at FAANG and other tier-1 tech companies.

Core Java FAQs

Q1. Who is the developer of Core Java?

Sun Microsystems is the developer of Core Java.

Q2. How is Core Java different from Advanced Java?

Core Java is used for general-purpose application development. On the other hand, Advanced Java is used to develop web-based and mobile applications.

Q3. What is the significance of JVM in Core Java?

JVM or Java Virtual Machine offers a runtime environment to execute Java bytecode. It allows Java programs to run on any device/OS and optimizes program memory.

Q4. What is the purpose of the JIT Compiler in Core Java?

In Core Java, JIT or Just-In-Time compiler improves the performance by simultaneously compiling parts of the bytecode having similar functionalities.

Q5. What gives Core Java its “write once and run anywhere” nature?

The bytecode gives Core Java its “write once and run anywhere” nature by converting programs into class files (Byte Code). Byte Code is the intermediate language between machine code and source code.

Ready to Crack Core Java Interview Questions?

Keeping these Core Java interview questions in mind and preparing for your tech interview accordingly will surely increase your chances of cracking the interview.

If you need more guidance, register for IK’s webinar today to learn how to leverage exclusive interview preparation courses and mock interviews with experts.

Interview Kickstart has helped over 9,000 engineers land coveted offers from FAANG and tier-1 companies. Our instructors are technical leads and hiring managers at FAANG and know precisely what it takes to nail big tech interviews.

Want to learn more? Sign up for our FREE webinar on How to Nail Your Next Tech Interview.