Top 50 Java Interview Questions for Experienced Programmers

Clearing the job interview can get you closer to being hired as an experienced Java professional. When preparing for an upcoming experienced-level Java interview, review the questions the employer may ask you. By practising the answers to these questions ahead of time, you can prepare well for your interview. In this article, we can review the common Java interview questions for experienced programmers and read a few example answers.

Ways to prepare for an experienced-level Java interview

Start your preparation by compiling a list of the most frequently asked Java interview questions and their answers. When making your selection, remember that your level of work experience with Java may determine the types of interview questions you get. If you have one or two years of experience, expect simple questions. You may get difficult questions based on advanced Java concepts if you have extensive Java programming experience.

Try to match your interview preparation with your experience level. If you are a new Java programmer, go over fundamental Java concepts, data structure, algorithms and API. Experienced programmers may benefit from reviewing core Java concepts like concurrency, OOPs, exception handling, string handling, synchronisation, collection framework and multi-threading. You can also study advanced Java topics like JDBC, JSP and Servlet, and popular frameworks like JSF, Hibernate ORM framework, Spring with Core, MVC, AOP, JDBC and ORM, Struts and SOAP & REST web services.

Basic Java interview questions

Irrespective of your levels of experience or skills, you may encounter these basic Java interview questions:

• Which Java project did you enjoy working on the most?

• Have you ever used Java to manage a team?

• Which object-orientated programming concepts have you used?

• Have you used a Request Dispatcher in a project?

• What do you know about JRE, JVM and JDK in Java?

• What do you know about wrapper classes in Java?

• Can you list the differences between the Array list and vector?

• Can you list the differences between Heap and Stack Memory?

• Does the garbage collection process clean Heap or Stack Memory?

• What are the advantages of Java packages?

• How would you define a Java Class?

• What are the main OOP concepts in Java?

• How would you reverse a string in Java?

• How would you compare two strings in Java?

• What do you know about API in Java?

Java interview questions for experienced professionals

When applying for an experienced-level Java position, the interviewer may ask you a few in-depth questions. What questions they choose to ask you often depends on your years of experience. Here are some common questions asked to candidates with different experience levels:

Java interview questions for candidates with one year of experience

If you have one year of experience, practise answering these Java interview questions:

• Who was the inventor of Java?

• Is Java a purely object-oriented language?

• Why is Java known as a platform-independent language?

• What is constructor overloading?

• In Java, what are the differences between abstract class and interface?

• Can Java support multiple inheritances?

• How important are keywords in Java coding?

• In Java, when can you use a composition?

• What is the difference between the equals method and equality operator?

• How do you declare an infinite loop in Java?

• What is data encapsulation in Java?

• What is garbage collection in Java?

• What does the garbage collection process achieve?

• Can you override the static methods?

• Can you explain the differences between this() and super()?

Related: 100 Java Interview Questions for Freshers With Example Answers

Java interview questions for candidates with two years of experience

If you have two years of experience, prepare for these Java interview questions:

• In OOP, why is composition more advantageous than inheritance?

• What is the Java thread life cycle?

• What is the advantage of an unordered array over an ordered array?

• What are marker interfaces in Java?

• What is “Double Brace Initialisation” in Java?

• How do you make an object eligible for garbage collection (GC) in Java?

• Have you completed a project using Java 11?

• Can you explain the working of substrings in String?

• How do you use business logic to complete an equality check?

• How do you use a numeric promotion?

• Can you estimate the time for code execution without a profiling tool?

• Why are strings made immutable in Java?

• What are the differences between interfaces and abstract classes?

• What are the differences between a HashSet and a TreeSet?

• Would you prefer the character array over string for securing information? Why?

Related: 30 Java Multithreading Interview Questions and Answers

5 Java Interview questions with example answers

Here are some Java interview questions for candidates with three years of experience and their example answers:

1. How can you use the Hibernate Framework in your everyday tasks?

The interviewer may ask this question to test your knowledge of the Hibernate Framework. Your response can include a brief explanation of Hibernate Framework and its uses.

Example answer: "The Hibernate Framework is a Java framework that you can use to simplify Java application development and database interactions. As an open-source, object-relational mapping (ORM) tool, it enables data creation, manipulation and access. It maps the object to the database data and internally uses the Java Database Connectivity (JDBC) API to interact with the data.

With the Hibernate Framework, you can automatically create tables in the database and gather data from multiple tables. It implements specifications of the Java Persistence API (JPA) for data persistence. Since the Hibernate Framework internally uses a default first-level cache and a second-level cache, it performs fast. You can use the object-oriented Hibernate Query Language (HQL) to generate database-independent queries. By using HQL, you do not need to change the SQL query and write database-specific queries to make any database changes."

Related: Important Hibernate Interview Questions and Answers to Them

2. Would you use String or StringBuffer for extensive data updates?

Interviewers may ask this question to assess your understanding of using String or StringBuffer to update data. You can explain which is the better option and why.

Example answer: "StringBuffer is a better option when you have extensive data updates. Since it is dynamic and mutable or modifiable, StringBuffer can grow and make room for additional character sequences and substrings. String, on the other hand, is immutable and has a fixed length. Every time you modify or update the String, it creates a new String. Over time, this causes the string pool to overload with objects you do not even need. That does not happen with StringBuffer since it can keep on modifying and accommodating changes."

3. In OOP, what is polymorphism?

Since polymorphism in Java allows developers to perform one action in different ways, it enables code reusability. The interviewer may ask this question to find out if you know how to use this Java feature.

Example answer: "Polymorphism is an important object-oriented programming language feature that enables you to present one interface for implementing different data types. The word polymorphism is a combination of poly or many and morph or form, and it means many forms. With polymorphism, it is possible to do one action in multiple ways. So, objects functions and variables can have several forms.

You can get two types of polymorphism in Java: compile-time or static polymorphism and runtime or dynamic method dispatch polymorphism. Function or operator overloading can lead to compile-time polymorphism, but as there is no Java support for this, go with method overloading. You can use method overriding to achieve runtime polymorphism."

4. What are the different types of inheritance in Java?

Java developers must understand the concept of inheritance to use existing classes to build new ones. So, expect this question at a Java job interview. In your answer, provide a brief explanation of each inheritance type.

Example answer: "Java can support different types of inheritance, such as single inheritance, multiple inheritances, multilevel inheritance, hierarchical inheritance and hybrid inheritance. In single inheritance, a class can extend to only one other class and confers it with its properties. When one class can extend to several classes, it is multiple inheritances. Java and other Object-Oriented programming languages do not support multiple inheritances. You can only achieve it in Java with interfaces.

In multilevel inheritance, one class can extend to another, and that class can then extend further to yet another class. Hierarchical inheritance is when one class can extend to many sub-classes. Hybrid inheritance is a combination of single inheritance and multiple inheritances."

Related: 15 Java 8 Interview Questions (With Example Answers)

5. What are the differences between static and non-static methods in Java?

This question is to test your understanding of using static and non-static methods. Your answer can include the use of keywords, compile-time and runtime.

Example answer: "For creating the static method in Java, you must use the static keyword before the method name. With the non-static method, using the static keyword before the name of the method is not necessary. In Java, a static method is part of the class, and a non-static method is part of the object of a class. You do not need to create an instance of the class to access the static method, but creating an instance of the class is essential for accessing the non-static method.

A static method can call only other static methods, not a non-static method, and it can access only static variables, not a non-static variable. A non-static method, on the other hand, can call a static method and access a static variable. The syntax to call a static method using the class is className.methodName. You can call it a non-static method like any method."

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