Top 37 Java 8 Interview Questions And Answers 2023

Java is one of the most prestigious companies that you can work for. You will be agreed with us when we say that this is a dream job for many of us who are visiting the page. The great pay, the great opportunities and a way to improve yourself intellectually and technologically is what attract job seekers to this job. There are so many perks of a job at java 8 that you need to know about. To get a Java 8 job, you need to clear the interview and impress the employers.
This is what intimidates the candidates most. Especially those who have never been to a Java 8 interview. But don’t worry we have got you covered. Here we are going to present a list of most asked Java 8 interview questions that will help you.
java 8 interview questions

Java 8 Interview Questions And Answers

Q1. What new features were added in Java 8?
Java 8 ships with several new features but the most significant are the following:
Lambda Expressions − a new language feature allowing treating actions as objects
Method References − enable defining Lambda Expressions by referring to methods directly using their names
Optional − special wrapper class used for expressing optionality
Functional Interface – an interface with maximum one abstract method, implementation can be provided using a Lambda Expression
Default methods − give us the ability to add full implementations in interfaces besides abstract methods
Nashorn, JavaScript Engine − Java-based engine for executing and evaluating JavaScript code
Stream API − a special iterator class that allows processing collections of objects in a functional manner
Date API − an improved, immutable JodaTime-inspired Date API
Along with these new features, lots of feature enhancements are done under-the-hood, at both compiler and JVM level.
Q2. What is the meaning of String::valueOf expression?
It is a static method reference to the valueOf method of the String class.
Q3. What is Optional? How can it be used?
Optional is a new class in Java 8 that encapsulates an optional value i.e. a value that is either there or not. It is a wrapper around an object, and you can think of it as a container of zero or one element.
Optional has a special Optional.empty() value instead of wrapped null. Thus it can be used instead of a nullable value to get rid of NullPointerException in many cases.
Q4. Tell us about the new Date and Time API in Java 8
A long-standing problem for Java developers has been the inadequate support for the date and time manipulations required by ordinary developers.
The existing classes such as java.util.Date and SimpleDateFormatter aren’t thread-safe, leading to potential concurrency issues for users.
Poor API design is also a reality in the old Java Data API. Here’s just a quick example – years in java.util.Date start at 1900, months start at 1, and days start at 0 which is not very intuitive.
These issues and several others have led to the popularity of third-party date and time libraries, such as Joda-Time.
In order to address these problems and provide better support in JDK, a new date and time API, which is free of these problems, has been designed for Java SE 8 under the package java.time.
Q5. What is stream pipelining in Java 8?
Stream pipelining is the concept of chaining operations together. This is done by splitting the operations that can happen on a stream into two categories: intermediate operations and terminal operations.
Each intermediate operation returns an instance of Stream itself when it runs, an arbitrary number of intermediate operations can, therefore, be set up to process data forming a processing pipeline.
There must then be a terminal operation which returns a final value and terminates the pipeline.
Q6. What is the difference between map and flatMap  stream operation?
There is a difference in signature between map and flatMap. Generally speaking, a map operation wraps its return value inside its ordinal type while flatMap does not.
For example, in Optional, a map  operation would return Optional<String> type while flatMap  would return String type.
So after mapping, one needs to unwrap (read “flatten”) the object to retrieve the value whereas, after flat mapping, there is no such need as the object is already flattened. The same concept is applied to mapping and flat mapping in Stream.
Both map and flatMap are intermediate stream operations that receive a function and apply this function to all elements of a stream.
The difference is that for the map, this function returns a value, but for flatMap, this function returns a stream. The flatMap operation “flattens” the streams into one.
Q7. What is the difference between intermediate and terminal operations?
Stream operations are combined into pipelines to process streams. All operations are either intermediate or terminal.
Intermediate operations are those operations that return Stream itself allowing for further operations on a stream.
These operations are always lazy, i.e. they do not process the stream at the call site, an intermediate operation can only process data when there is a terminal operation. Some of the intermediate operations are filter, map  and flatMap.
Terminal operations terminate the pipeline and initiate stream processing. The stream is passed through all intermediate operations during terminal operation call. Terminal operations include forEach, reduce, Collect and sum.
Q8. What is a stream? How does it differ from a collection?
In simple terms, a stream is an iterator whose role is to accept a set of actions to apply on each of the elements it contains.
The stream represents a sequence of objects from a source such as a collection, which supports aggregate operations. They were designed to make collection processing simple and concise. Contrary to the collections, the logic of iteration is implemented inside the stream, so we can use methods like map and flatMap for performing a declarative processing.
Q9. What is jjs?
In Java 8, jjs is the new executable or command line tool used to execute Javascript code at the console.
Q10. What is Nashorn in Java8?
Nashorn is the new Javascript processing engine for the Java platform that shipped with Java 8. Until JDK 7, the Java platform used Mozilla Rhino for the same purpose. as a Javascript processing engine.
Nashorn provides better compliance with the ECMA normalized JavaScript specification and better runtime performance than its predecessor.

Java 8 Interview Questions For 10 Years Experience

1.Why do we need change to Java again?
2.Java SE 8 New Features?
3.Advantages of Java SE 8 New Features?
4.What is Lambda Expression?
5.What are the three parts of a Lambda Expression? What is the type of Lambda Expression?
6.What is a Functional Interface? What is SAM Interface?
7.Is is possible to define our own Functional Interface? What is @FunctionalInterface?
8.What are the rules to define a Functional Interface?
9.Is @FunctionalInterface annotation mandatory to define a Functional Interface?
10.What is the use of @FunctionalInterface annotation? Why do we need Functional Interfaces in Java?
11.When do we go for Java 8  Stream API? Why do we need to use Java 8 Stream API in our projects?
12.Explain Differences between Collection API and Stream API?
13.What is Spliterator in Java SE 8?
14.Differences between Iterator and Spliterator in Java SE 8?
15.What is Optional in Java 8? What is the use of Optional?Advantages of Java 8 Optional?
16.What is Type Inference? Is Type Inference available in older versions like Java 7 and Before 7 or it is available only in Java SE 8?

Java 8 Programming Questions

Question1. Can you convert an array to Stream? How?
Yes, you can convert an array to Stream in Java. The Stream class provides a factory method to create a Stream from an array like Stream.of(T …) which accepts a variable argument, that means you can also pass an array to it as shown in the following example:
String[] languages = {“Java”, “Python”, “JavaScript”};
Stream numbers = Stream.of(languages);
So, yes, it’s possible to convert an array to Stream in Java 8. You can even convert an ArrayList to Stream as explained in that article.
Question2. What is the parallel Stream? How can you get a parallel stream from a List? Answer:
A parallel stream can parallel execute stream processing task. For example, if you have a parallel stream of 1 million orders and you are looking for orders worth more than 1 million then you can use a filter to do that.
Unlike sequential Stream, the parallel stream can launch multiple threads to search for those orders on the different part of Stream and then combine the result.
In short, the parallel stream can paralyze execution but, as Cay S. Horstman mentioned in Core Java SE 9 for the Impatient, there is significant overhead or parallelism which only pays off if you are doing bulk data operation.
Question3. What is a Predicate interface? Answer:
A Predicate is a functional interface which represents a function, which takes an Object and returns a boolean. It is used in several Stream methods e.g. filter() which uses Predicate to filter unwanted elements.
here is how a Predicate function looks like:
public boolean test(T object){
   return boolean;
You can see it just has one test() method which takes an object and returns a boolean. The method is used to test a condition if it passes it returns true otherwise false.
Question4. What is difference between findFirst() and findAny() method?
The findFirst() method will return the first element meeting the criterion i.e. Predicate  while findAny() method will return any element meeting the criterion, very useful while working with a parallel stream. You can further see this  article for a working example of findFirst()  method in Java 8.
Question5. What is the difference between a normal and functional interface in Java? Answer:
The normal interface in Java can contain any number of the abstract method while the functional interface can only contain just one abstract method.
You might be thinking why they are called functional interface? Once you know the answer, it might be a little easier for you to remember the concept.
Well, they are called functional interface because they wrap a function as an interface. The function is represented by the single abstract method on the interface.
Question6. What do you mean by saying Stream is lazy? Answer:
When we say Stream is lazy we mean that most of the methods defined on class is lazy i.e. they will not work by just including them on Stream pipeline.
They only work when you call a terminal method on the Stream and finish as soon as they find the data they are looking for rather than scanning through the whole set of data.
Question7. What does peek() method does? When should you use it?
The peek() method of Stream class allows you to see through a Stream pipeline. You can peek through each step and print meaningful messages on the console. It’s generally used for debugging issues related to lambda expression and Stream processing.

Conclusion –

Here our job is done. We have presented a list of good Java 8 questions that will help you to get the job at Java 8. These questions will certainly enhance your chances of getting the job. Thank you for visiting us and we hope our article was helpful for you.

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