15 Java 8 Interview Questions (With Example Answers)

Updated 19 October 2022

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Java 8 is an updated version of Java released in 2014. Developers today need to have skills in multiple programming languages to secure a job and Java 8 is one such primary language. If you're appearing for a Java 8 programmer interview, you'll have to face questions about your practical knowledge and coding experience. Preparing for these questions in advance will give you the confidence you need to succeed in your interview.

In this article, we will discuss multiple Java 8 interview questions you may have to face in your interview and the example answers for these questions.

Common Java 8 Interview Questions And Example Answers

Here are some common interview questions that you may be asked in a Java 8 interview, along with example answers:

1. What is a 'method reference' in Java 8?

The interviewer may ask this question in the initial phase of the interview to test your knowledge of Java 8. Being able to speak eloquently on specific features of Java 8 is important for you to showcase you possess the skill set to be a good programmer. To answer this question, describe a method reference using adequate detail in a simple format that is clear and easy to understand.

Example: "A method reference in Java 8 is a feature that allows for the definition of Lambda Expressions. This is done by referring to methods using their names."

2. Explain 'functional interfaces'.

The interviewers ask this question to check if you have the foundational knowledge required to perform certain tasks with Java 8 that might be necessary for the job. To answer this question, briefly explain the concept and mention any applications you know of.

Example: "A functional interface is an interface that has only one abstract method. These interfaces provide the target for Lambda expressions that implement them."

3. What is a 'SAM interface'?

Sometimes, it's necessary to show you understand basic technical concepts that might be important to the position. To answer this question, briefly explain the concept and add any relevant information you know to highlight your understanding of the concept.

Example: "A Single Abstract Method interface or SAM interface reflects an interface with one abstract method. A SAM interface is also known as a functional interface and both these terms can be used interchangeably."

4. In Java 8, what does 'stream pipelining' mean?

This question tests your understanding of the foundational concepts. To answer this question, restate the concept and then offer a concise definition.

Example: "Stream operations often return themselves for pipelining. When this occurs, an intermediate operation takes them in, processes them and outputs again. At the end of the stream, a collect method usually occurs."

5. What are 'collectors' and 'statistic collectors'?

The interviewers ask this question to check your knowledge on two subjects, collectors and statistic collectors. To answer this question, compare the two briefly.

Example: "On a string of code, collectors work to combine all results from processing. Statistic collectors calculate statistics while processes occur."

6. Explain 'Optional' in Java 8?

This is a concept-based question. When asked to explain a concept, you should describe it in your own words so the interviewer can see how you speak to others in a professional setting. It's an opportunity for you to show a little personality besides strong communication skills.

Example: "Optional is a form of containerisation that holds non-null objects. The Optional object that remains is defined as null with absent value."

7. How does Java 8 achieve platform independence?

The interviewers may ask you this question to check how much you know about Java 8 and if you know the difference between Java 8 and dependent programming languages like C/C++. The recommended way for you to answer this question is by explaining the features that provide platform independence to Java.

Example: “Java achieves platform independence due to features like class files, bytecode and Java Virtual Machine (JVM). Since all Java programs run on JVM, there is no dependence on a particular platform.”

8. How do the 'interface' and 'abstract' classes differ in Java 8?

This is a popular Java 8 interview question. To answer this question, mention the differences between the two classes. You may also mention how Java 8 allows non-abstract methods on the interface.

Example: “'Abstract' is a class that can be modified by non-abstract methods, but the 'interface' cannot have instance variables because it cannot have a state. Another difference between the two is that you can define constructors inside an 'abstract' class, but the same is not possible in the 'interface'.”

9. Explain the difference between 'transient' and 'volatile' variables.

The interviewers ask this question to check your knowledge about variables in Java. To answer this question, briefly explain the differences between the two types of variables.

Example: “The major difference between these two types of variables is that 'transient' variables are not serialised during the serialisation process, whereas 'volatile' variables are special and get their value from multiple threads within a Java application. A volatile variable's value should always be read from the main memory instead of cached values.”

10. What is the difference between 'wait' and 'sleep' methods in Java 8?

This is a prevalent question often asked in Java 8 interviews. The interviewers ask this question to test your knowledge of the different methods in Java 8. To answer this question well, briefly explain the differences between the two functions.

Example: “Both 'wait' and 'sleep' methods are used to put a thread in a waiting state, but their applications and nature are different. The 'wait' method puts a thread in a waiting state, while the 'sleep' method is used to pause an entire Java application.”

11. How can you override a static method in Java 8?

The interviewers may ask this question to confuse you. The trick here is that you cannot override the static method in Java 8. Interviewers ask you such questions to check your presence of mind and how much attention you pay to details. To answer this question, state clearly that it's not possible to override a static method in Java 8 and explain the reason for it.

Example: “You cannot override a static method in Java because method overriding happens at runtime due to dynamic binding and static methods are bonded using static binding at compile time. Static methods are resolved before the creations of objects, making it impossible to override static methods.”

12. In Java 8, what's the difference between 'this' and 'super' keywords?

This question tests your knowledge of the basic Java 8 concepts. To answer this question, briefly explain the two keywords along with their applications.

Example: “this() represents the current instance of a class and super() represents the current instance of the parent class.”

13. Does Java 8 support multiple inheritances?

The interviewers ask this question to test your knowledge of inheritance. To confidently answer such a question, pause and think for a moment. The important thing here is to understand the language of the question. Once you are clear about the concept being tested, you can answer such questions easily.

Example: “No, Java 8 does not support multiple inheritances. The reason behind this is to avoid ambiguity in cases where multiple child classes may inherit similar properties, making it unclear for the compiler to know which method should be invoked.”

14. Is it possible to access the 'private' method in Java 8?

The interviewers ask this question to check how much you know about access-restriction and encapsulation in Java 8. To answer this question, answer in the affirmative and name the condition that needs to be satisfied for this operation.

Example: “Yes, we can access the 'private' method in Java 8. However, it needs to be in the same class and not outside it.”

15. What are the similarities and differences between 'ArrayList' and 'LinkedList'?

The interviewers ask this question to test your working knowledge of how data structures work in Java 8. To answer this question well, briefly explain the similarities and differences between the two. You may get some follow-up questions about how different methods behave for these two data structures and so it would be a good idea to read up on this.

Example: “If we talk about the similarities, both 'ArrayList' and 'LinkedList' are ordered, index-based and allow duplication. Both these lists are not synchronised, which means you need external synchronisation to share them between multiple threads. Speaking of the differences, the 'ArrayList' depends on an array and 'LinkedList' depends on the linked list data structure, which makes methods like add, remove and contain perform differently for each of the two.”