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Top 30 Java 8 Interview Questions & Answers (2023)

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James Gosling and his team were cleaning up C++ when they accidentally created a new language, which is today one of the most well-known and frequently used programming languages available. Yes! Your guess is correct; we are talking about Java

java 8 interview questions

Java developers upgraded its features and launched various Java versions as time passed. Java 8 is a game-changing update to the world's most popular development platform. Oracle introduced Java 8 in March 2014, with features such as Lambda Expressions, making history in the field of coding languages by providing a faster and upgraded JVM that allows programs to run more efficiently.

This article aims to discuss Java 8 Interview Questions that are asked frequently.

Basic Level Java 8 Interview Questions

1. What are some of the new features in Java 8?

Ans: This is one of the most basic and important Java 8 Interview Questions.
Many vital features for Java programming have been implemented in Java 8. The following are some of these characteristics:
Lambda Expression.
Default methods for Implementing Interfaces.
Nashorn, to evaluate and execute JavaScript code.
Stream API.
Date and Time API.

2. What is the meaning of a lambda expression?

Ans: The lambda expression was introduced in Java 8 to offer users an anonymous function that can be called without specifying a function name and contains a set of parameters that may be used with a lambda entity.
A lambda expression has the following structure:
(Argument List) -> {Statements;}

3. What are the main parts of a lambda expression?

Ans: There are three parts to a Java lambda expression.
1) Argument-list: This might be either empty or non-empty.
2) The arrow token: It connects the arguments list with the expression body.
3) Body: It contains lambda expression expressions and statements.

4. What are the most significant benefits of Java 8?

Ans: The release of Java 8 has proven to be highly beneficial to programmers in the following ways:
The code is now highly readable.
More code reusability.
The code is now relatively small.
Execution and operations in parallel.
Concurrent and Scalable Codes.
Better Performance of Applications.

5. What is the definition of a functional interface?

Ans: An interface with only one abstract method is a functional interface. Functional interfaces' primary objective is to make it possible for lambda expressions or method references to be used to build instances of these interfaces more concisely and expressively. As a result, using functional-style programming features like constructing callbacks and providing behaviour as parameters to methods are made simpler.

6. What does Java 8 mean by functional interfaces?

Ans: In Java 8, functional interfaces are interfaces with only one abstract method.
The three sorts of methods that can be used are as follows:
The Static method.
The Default Method.
The Method of Overridden class.

7. Where can we use the @FunctionalInterface annotation?

Ans: This annotation is used in functional interfaces to make the code more readable and informative. However, it does not affect the code's execution or semantics.

8. In the context of Java 8, what does "method reference" mean?

Ans: A method reference is a Java 8 construct that allows you to refer to a method without calling it. It is a concise Lambda expression approach. When using functional interfaces (interfaces with a single abstract method), method references are very helpful since they allow you to send a method as a parameter to a higher-order function or utilise it as a lambda expression. By eliminating the need for unnecessary code, they assist in making your code more readable and concise.

9. What is Type Inference, and how does it work?

Ans: By examining each method invocation and its related declaration, type inference assists the compiler in determining the parameter types. When using functional interfaces (interfaces with a single abstract method), method references are very helpful since they allow you to send a method as a parameter to a higher-order function or utilise it as a lambda expression. By eliminating the need for unnecessary code, they assist in making your code more readable and concise.

10. Why are default methods in the interface required?

Ans: Default methods allow you to extend the functionality of your libraries' interfaces while maintaining binary compatibility with earlier code. Before the start of Java 8, if you wanted to add a new method to an interface, all classes that implemented that interface would become broken since they would now need to provide an implementation for the new method. This was a challenge for libraries and APIs that were already in use broadly because adding new methods could cause codebase disruption.

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Intermediate Level Java 8 Interview Questions 

11. What is the purpose of the StringJoiner class in Java 8?

Ans: The StringJoiner class in Java 8 creates a sequence of characters separated by a delimiter, allowing users to generate a string by passing delimiters such as hyphens and commas. 

12. In Java 8, what are PermGen and Metaspace?

Ans: Until Java 7, the Java Virtual Machine used PermGen for class storage. Metaspace has now taken its place. Metaspace has a significant benefit over PermGen in that it can grow indefinitely without constraint, whereas PermGen has a set maximum size.

13. What is the difference between a stream and a collection?

Ans: A stream is an iterator that accepts a set of actions and applies them to each component in its collection. A stream is an object sequence that facilitates aggregate operations from a collection or other source. Iteration logic, unlike collections, is implemented within the stream.
In addition, unlike collections, streams are loaded and processed slowly.

14. In Java 8, what is Nashorn?

Ans: Nashorn is a new JavaScript processing engine pre-installed with Java 8. It Complies more closely with ECMA JavaScript requirements and outperforms Rhino's runtime performance.

15. In Java 8, what is jjs?

Ans: jjs is a new console executable or command-line tool for executing JavaScript code. The Nashorn JavaScript Engine can be used in conjunction with the jjs utility to run JavaScript code straight from the command line. It can be used for Java applications integration, testing, and scripting of JavaScript code. When using JavaScript code to interface with Java classes and libraries, this integration is very useful.

Java 8 Interview Questions for Experienced

16. What exactly is stream pipelining?

Ans: The concept of stream pipelining is the linking of operations. This is accomplished by categorising the operations on a stream into two groups. "Intermediate operations" and "terminal operations" are their terms. When each intermediate operation completes, it returns an instance of Stream; thus, an arbitrary number of intermediate operations can be used to process data, forming a processing pipeline. The pipeline must then be terminated using a terminal operation that returns a final value.

17. How do you distinguish between findFirst() and findAny()?

Ans: When working with a parallel stream, findFirst() returns the first element that meets the criterion, whereas findAny() returns any element that meets the standard. The main difference between findFirst() and findAny() is how they behave when dealing with parallel processing and order.
Use findFirst() to get the first element according to the stream's or source's order.
Use findAny(), especially when working with parallel streams to potentially enhance efficiency, if you need any element that satisfies a criteria and the order doesn't matter.

18. In Java 8, which class implements the encoder for encoding byte data?

Ans: The static class Base64.Decoder implements the encoder that can easily encode byte data using the Base64 encoding strategy. The Base64 encoding is well suited for tasks like sending binary data in a text-based format since it is frequently used to represent binary data as ASCII text.

The Base64.Encoder class, an inner class of the Base64 class, can be used in Java 8 to encode bytes using the Base64 encoding technique. 

19. In Java 8, how do you make a Base64 decoder?

Ans: The Base64.Decoder is returned via the getDecoder() method, part of the Base64 class. The Base64 encoding technique is used to decode this. This class offers ways to convert data that has been Base64-encoded back to binary form. Keep in mind that a java.lang.IllegalArgumentException will be raised if the encoded data is not a legitimate Base64-encoded string. Therefore, when working with decoding operations, you should handle exceptions appropriately.

20. In Java 8, what is a supplier?

Ans: In Java 8, a supplier is a simple, functional interface that does not accept arguments. When using lambda expressions, it is used as an assignment target. A functional interface from the java.util.function package in Java 8 is called a Supplier. It depicts a value supplier, a practical idea utilised to offer a value devoid of consideration for any arguments to counter. A single abstract method called get(), which takes no arguments and returns a value of a certain type, is present in the Supplier interface.

Advanced Level Java 8 Interview Questions 

21. In Java 8, what is a consumer?

Ans: A consumer is a single argument functional interface in Java 8. The consumer returns no value and can be used in lambda expressions.  It symbolises an operation that uses just one input argument and applies some action to it without producing any output. A single abstract method named accept(), which accepts an argument of a certain type and returns nothing (void), is present in the Consumer interface.

22. In Java 8, distinguish between Collection API and Stream API.

Ans: The differences are as follows:

Key PointsCollection APIStream API
BasicHelps in Data StorageHelps in Data Processing
SizeOnly holds a small number of itemsIt is possible to store an infinite number of elements
ExecutionFast ExecutionSlow Execution


23. What are the similarities between Java 8's map and flatMap stream operations?

Ans: Both map and flatMap actions are intermediate stream operations that accept a function as input and utilise it to do various actions in the stream. It is possible to apply a function to each element in a stream using the map() and flatMap() procedures. Map() and flatMap() are both intermediary processes; they don't result in a final product on their own. They frequently work together with other stream operations.
Both actions maintain the stream's nature. Applying map() or flatMap() to a stream of type Stream<T> will create a new stream of the same type.

24. Give some examples of Intermediate Operations(methods) in Java 8?

Ans: In Java 8 intermediate operations, the following are some examples:

25. In Java 8, what are some examples of terminal operations?

Ans: Some examples of terminal operations in Java 8 are as follows:

26. In Java 8, what is the purpose of the peek() method?

Ans: In Java 8, the peek() method is part of the stream class, and it's used to view what's happening in a stream pipeline. Peeking can be done to print messages to the terminal about the code being executed.
When performance is a must, debugging code with the lambda expression, or conducting stream processing, Peeking comes in handy.

27. In Java 8, what is the syntax of a predicate interface?

Ans: In Java, a predicate is a functional interface that accepts an object and returns a Boolean value.
A predicate function has the following syntax:
public boolean example(T object){
return boolean;

28. Why do you believe you are the best candidate for this Java Developer position

Ans: In a Java 8 interview questions, this is a relatively popular question. The interviewer is interested in learning more about our Java skills and how we plan to use them to advance our careers.
Answering this question based on your interests in Java programming and how you plan to apply it to the best of your ability when you join the firm would be helpful.

29. Do you have any prior experience working in a similar field to ours?

Ans: This is a specific Java 8 Interview question for the company you have applied to. Java 8 is used in various sectors to meet their specific needs. Understanding the job description and what is expected of you and discussing any past work experience you have in the same industry will assist you in answering this question.

30. Do you have any prior experience working in a Java-based production environment

Ans: If you are an experienced developer being interviewed, this question will likely come up in your Java 8 Interview Questions. Make sure to answer it completely and honestly about your experience with Java development in a production context.

Frequently Asked Questions

How to prepare for Java 8 interview?

One should follow some steps while preparing for Java 8 interview, such as reviewing critical concepts like lambdas, functional interfaces, default methods, etc. Understand the features of Java 8, such as optional classes, the date and time API, and many more. Practice more coding questions that have appeared in the last ten years from online sites.

What are the main Java 8 features?

There are different features of Java 8 like Default and Static methods, Lambda and Functional Interfaces for functional programming, API streams for data processing, Optional class used to handle NULL values, have Date and Time API used in date and time manipulations. These are some main features of Java 8.

What is the main purpose of Java 8?

The primary objective of Java 8 was to present new components and enhancements to the Java programming language. It aimed to enhance developer productivity, code readability, and implementation. Java 8 got features such as lambdas, streams, default methods, the Optional class, and the Date and Time API, allowing developers to write more expressive, efficient, and modern code for different application domains.

What is lambda expression in Java 8 interview questions?

In Java 8, an important feature, lambda expressions, was added to assist functional programming. They offer a clear way to express anonymous functions or blocks of code that can be utilised in functional programming constructs or passed as arguments to methods.


We’ve concluded our Java 8 interview questions. This article covered some of the most common interview experiences you might encounter during your Java 8 Interview Questions.

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We wish you Good Luck! Keep coding and keep reading Ninja!!

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