Introduction
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 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.
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.