101 Most Common Java Interview Questions (2024)

The key to Java interviews is being able to thoroughly answer any questions that come your way. The best way to do so? Practicing20 some common Java interview questions beforehand.

In our comprehensive guide, we’ll explain the different types of Java interview questions you could face, some helpful ways to prepare for the interview, over 100 common questions, and common mistakes to avoid during your interview.

Types of Java Interview Questions

In your interview, you’ll be faced with many types of questions.

Here are the five main types of Java interview questions to be aware of.

Core Java interview questions

The core Java interview questions you’ll face are meant to demonstrate to the interviewer that you’re familiar with Java basics. Not only that, but core questions also help the interviewer see that you’re able to use the language efficiently and effectively. 

Core questions could include things like:

• Control flow statements
• Exception handling
• Data types
• Object-oriented programming

Advanced Java interview questions

Advanced Java interview questions take it a step further. These questions go beyond the fundamentals and into the more complex parts of Java. The interviewer asks these questions to see how advanced your knowledge of the language is as well as your ability to solve programming challenges head-on.

Questions might revolve around topics like:

• Design patterns
• Generics
• Collections
• Multithreading

Design patterns questions

To get an idea of how much you know about structuring and organizing code, interviewers will often ask design patterns questions. They want to know if you understand how to make your programs reusable, efficient, and more maintainable. To do so, they might ask you to identify when a certain design pattern is better to use or to explain particular design patterns, among other things.

Problem-solving questions

One of the most common types of Java interview questions is the problem-solving questions. These questions test your ability to solve issues through programming and logic. The interviewer wants to make sure you can look at a problem, brainstorm solutions, and then write a program that functions like it should. 

Oftentimes, these questions are timed, so you’ll have to solve a coding problem before the time runs out. When facing these questions, be prepared to explain your answer and your approach.

Behavioral questions

Many types of interviewers use behavioral questions to gauge how you’d react in a certain situation, and Java interviews are no different. Behavioral questions help the interviewer get an idea of your work ethic, your soft skills, and how you’d fit into the work culture at the company. 

The answers you give for these questions will help the interviewer see how you might handle similar challenges or obstacles in the future. 

5 Ways to Prepare for Java Interview Questions

As soon as you get the interview scheduled, it’s time to prepare. 

Check out these five easy ways to prepare for answering Java interview questions and making the most out of your interview. 

1. Take time to review the fundamentals of Java.

Even if you feel confident about your knowledge of Java basics, it doesn’t hurt to brush up on the fundamentals. Some candidates feel overly confident about the basics and don’t realize they’ve forgotten key concepts.  

Some essentials you might want to review include areas like:

• Collections
• Polymorphism
• Methods
• Data types
• Generics
• Inheritance 
• Control flow statements
• Objects and classes

You can review these with a number of different resources, from textbooks to online tutorials and sites. 

It’s also a good idea to practice coding and use a debugger to find any potential errors. 

2. Be prepared to explain your code.

People who work in programming often assume they’re prepared to explain their code. After all, they wrote it. However, explaining your code is more than just telling someone how it works. 

To prepare how to explain your code during a Java interview, you need to:

• Know the logic behind it
• Be able to explain it in plain language without using any technical vocabulary
• Be ready to justify or explain any design decisions
• Be able to walk someone through it, step by step
• Be prepared to answer questions about it

3. Be ready to discuss your experience with Java.

Discussing your experience with Java is more than just recounting when you’ve used it. Before the interview, plan out what you’ll say when asked to talk about your experience. 

For example, think about your most recent (and relevant) projects to show the interviewer you have the skills and qualifications they’re looking for. It’s also important to quantify that experience whenever possible by mentioning how long you worked on the project and how much total Java experience you have. 

Be ready to explain projects that you worked on with others and what your role was with specific examples to illustrate your experience. 

The interviewer might also ask about challenges you’ve faced, so jot down a few obstacles you’ve run into and how you solved them.  

4. Make sure you’re prepared to problem solve. 

Knowing how to solve problems is often a huge part of answering Java interview questions which is why it’s crucial to prepare. To do so, practice as much as you can. 

You can use online resources — such as LeetCode, CodingBat, or HackerRank — and problems that you find in your reading material. Make sure you’re not just practicing one type of problem. Instead, practice data structures, algorithms, and concurrency problems, too. 

Make sure when you practice, you also test your code and ensure you have a correct solution. 

5. Practice answering Java interview questions out loud.

It should be no surprise that you’ll also need to practice answering Java interview questions out loud. To take it a step further, use an online interview simulation like Yoodli. 

This communication coach analyzes the way you answer questions and provides direct feedback on how you can improve your responses. In other words, you’ll get personalized suggestions for your own improvement. To learn more, check out our overview video on how Yoodli works.

Using generative AI, Yoodli offers users a realistic interview experience where you can choose which questions to practice, including Java interview questions. Create a couple of your own questions or pull some directly from Yoodli’s question inventory. To personalize the interviewer, you can choose the type of interview you’re looking for, whether that’s professional and serious, friendly, or even technical. 

Once you’ve answered the questions, you can see all your personal metrics, from your speech pace to your word choice and how many filler words you used. Of course, you’ll also get to see Yoodli’s feedback. 

For example, if your speaking pace was a little too fast, Yoodli might suggest slowing down or using a few natural pauses while you answer your Java interview questions. 

Practicing some common Java interview questions is one of the best ways to gain a competitive edge against other candidates.

101 Most Common Java Interview Questions

Every interview is going to be different, but preparing with as many questions as possible is a great way to make sure you’re ready and prepared for the conversation. 

Here are 101 of the most common Java interview questions you could face in your interview.

1. What are the different types of data types in Java?
2. What is copy constructor?
3. List and explain the features of Java.
4. What would you say are your strengths and weaknesses?
5. What is inheritance?
6. What is the Java Virtual Machine?
7. What is constructor overloading?
8. Tell me about a time when you had to work with a difficult team member.
9. What’s the difference between a lambda expression and a method reference?
10. What is a constructor?
11. Tell me about a time when you had to solve a problem that was exceptionally challenging.
12. What’s the difference between a map and a stream?
13. What is a classloader?
14. What is a package?
15. How would you declare an infinite loop in Java?
16. Consider this source file name: Empty .java — Is it valid? 
17. Write a program that can evaluate whether or not a number is prime.
18. What’s the difference between a collect and a reduce?
19. What’s the difference between runtime and compile time errors?
20. What’s the default value of the local variables?
21. Write a program to find the highest number in an array.
22. What’s the difference between the equals() method and equality operator (==)?
23. Why do static methods and variables exist?
24. What is generics?
25. How would you explain the concept of the observer design pattern?
26. What are the pros to defining packages in Java?
27. What is exception handling?
28. Explain what a JIT compiler is.
29. What is an object-oriented paradigm?
30. Explain the concept of the singleton design pattern.
31. What is JDBC?
32. Does the constructor return any value?
33. List and explain the different types of design patterns.
34. What’s data encapsulation?
35. Can you make a constructor final?
36. What is EJB?
37. What’s the difference between a join and a fork?
38. What is hibernate?
39. With regard to static methods, what are the restrictions that are applied?
40. What is the spring framework?
41. What’s the difference between an anonymous inner class and a local class?
42. What is JMS?
43. What is the static block?
44. What is a design pattern?
45. What are servlets and JSP?
46. Could you execute a program without the main() method?
47. What’s the difference between an instance variable and a local variable?
48. When should you use a design pattern?
49. Can constructors be made static?
50. What is multithreading?
51. Explain the concept of the Factory Method design pattern.
52. Can the static variables and methods be declared in an abstract class?
53. Pointers, used in C/ C++, aren’t used in Java. Why not? 
54. What is a collections framework?
55. What’s “this” keyword in Java?
56. Write a program to reverse a string.
57. What is garbage collection?
58. Could you assign the reference to “this” variable?
59. How is Java different from C++?
60. Write a program to find the factorial of a number.
61. Using “this” keyword, how can constructor chaining be done?
62. What is a thread?
63. Write a program to find the sum of the first [any number] natural numbers.
64. What are the benefits of passing “this” into a method as opposed to the current class object?
65. Explain the concept of the Strategy design pattern.
66. In Java, what’s the difference between Heap and Stack Memory?
67. What’s the difference between an abstract class and an interface?
68. What is inheritance and what types are there?
69. Tell me about a time when you had to work with a team to complete a task.
70. What is polymorphism?
71. Explain the Decorator design pattern.
72. What is aggregation?
73. Write a program to print the Fibonacci sequence up to the [n^th] term.
74. For all the classes, which class is considered the superclass?
75. Why isn’t Java a pure object-oriented language?
76. What is composition?
77. Why are you interested in this position?
78. Why doesn’t Java support multiple inheritance?
79. In Java, what is “super”?
80. What’s the difference between an object and a class?
81. Explain why Java is a platform-independent language.
82. What are the differences between “super” and “this”?
83. Write a program to find the greatest common divisor of two numbers.
84. Explain the Adapter design pattern.
85. What’s object cloning? 
86. Write a program to find the least common multiple of two numbers.
87. What’s the difference between a flat map and a stream?
88. What’s method overriding?
89. Write a program to check if a string is a palindrome.
90. What are the differences between overriding and overloading?
91. Recall a time when you had to work under pressure. How did you handle it?
92. Can you override a private method?
93. Can you explain the concept of the Facade design pattern?
94. Explain the covariant return type.
95. What’s the “final” variable?
96. What’s the “final” method?
97. Explain the Template Method design pattern.
98. What’s the “final” class?
99. Write a program to find the length of the longest common subsequence of two strings.
100. Tell me about a time when you had to make a difficult choice.
101. Could you declare an interface as final in Java?

7 Mistakes to Avoid When Answering Java Interview Questions

One critical aspect of prepping isn’t just practicing Java interview questions, but also being aware of potential pitfalls and steering clear of them.

Here are the seven most common mistakes people make in these interviews and when answering Java interview questions and how you can avoid them. 

1. Not being adequately prepared

Of course, the biggest mistake people make with Java interviews is not being prepared enough. 

As mentioned above, the best way to prepare is to practice answering common Java interview questions with a simulator like Yoodli. Other ways to prepare include:

• Making sure you go over Java fundamentals
• Knowing how to explain your code
• Giving yourself a refresher on your Java experience

2. Being unable to actually explain your code

Make sure you’re able to fully explain your code. Even if you’re very confident in your code and how it works, that won’t be impressive to an interviewer if you aren’t able to explain it.  

Practice explaining some of your past code to a family member. It’s most helpful to practice explaining it to someone who doesn’t have a computer science or programming background. For example, how would you explain your code to your grandmother? Thinking about it in this way can help you get to the nuts and bolts of how to best explain your code in plain language. 

Still, make sure you can also explain the details, like the algorithms, data structure, and the overall logic behind it.

3. Rambling, monologuing, or talking too much

One of the little known (but common) mistakes boils down to talking too much. Answering Java interview questions causes some people to naturally ramble on and on or go on a monologue about their experience, processes, or other topics. 

To avoid this, make sure when you’re answering these Java interview questions that you’re concise. Simplifying concepts is OK too, especially as the interviewer can ask you to clarify or provide more detail. 

Using specific examples in interviews is definitely the right move. Just make sure you don’t go on a tangent. 

4. Coming off as arrogant

Although you want to show the interviewer that you’re skilled, knowledgeable, and enthusiastic during the conversation, you don’t want to come off as arrogant. This is a pitfall many people find themselves in during Java interviews. 

There’s a fine line between being self-confident and being arrogant. Don’t assume you know more than the interviewer. You can confidently explain your code and answer Java interview questions without being full of yourself.

5. Being unable to answer core Java interview questions

It’s a huge red flag for interviewers when a candidate isn’t able to answer basic, core Java interview questions. 

Some people might get nervous and forget, even if they know the information. However, this will still give the wrong impression to interviewers, whether you actually know the answers or not. 

6. Not being able to solve problems

If you work in programming, you might be a naturally talented problem-solver. One of the biggest mistakes to steer clear of is not being able to use Java to solve programming problems. 

If you’d consider this one of your weaknesses, consider practicing with a friend, getting tutoring, or brushing up on your knowledge through textbooks or workbooks. 

7. Not asking questions

This mistake isn’t just common in Java interviews, but all interviews. At the end of the conversation, the recruiter or interviewer will expect you to have questions about the company, teh position, or the work environment, for example. When people show up to the interview without questions, the interviewer might interpret this as the candidate “not caring” about the position. 

Make sure you have a brief list of interview questions for interviewers to ask at the end of the conversation. For example, you could ask about what the company’s doing to show its commitment to DEIB or how it fosters diversity and inclusion in the workplace. 

The Key Takeaway 

It’s exciting when you have a Java interview lined up. To make the most of the opportunity, make sure you practice some common Java interview questions and put in some prep work.  

It’s so worth preparing for an amazing opportunity than winging your answers on the fly. 

Sources

• Geeks for Geeks: “Java Tutorial.”
• InterviewBit: “Java Interview Questions.”
• Java Point: “300 Core Java Interview Questions.”
• Refactoring Guru: “Design Patterns in Java.”
• Indeed: “40 Advanced Java Interview Questions and Sample Answers.”
• Interview Cake: “Coding Interview Tips.”