Top 35 Java 8 Interview Questions and Answers in 2023

Java has been well known for adding various new features from time to time, and Java 8 SE is one of the more recent releases of the programming language. Released in March 2014, it focuses on overcoming the loopholes and drawbacks of earlier versions, along with adding new features and characteristics. Java 8 SE was developed with the purpose of implementing functional programming, creating a new JavaScript search engine, manipulating the date-time with new APIs, and deploying a new streaming API.

We list several of the most common Java 8 interview questions and answers here. We’ve split the questions into beginner and advanced questions.

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8. What are the features of a lambda expression?

The features of lambda expressions are:

It has no specific parameters.
It returns any kind of result.
It has the type “Java.lang.Runnable”

9. Define Optional in Java SE 8?

Optional is a final class that is introduced as an integral part of Java SE8. It is a java.util package that can have either one value or zero value.

10. What is the use of Optional in Java SE 8?

Optional in Java SE 8 is used for representing optional values that exist or does not exist. It does not support too many null checks and NullPointerException. In addition to that, it avoids the runtime NullPointerExceptions and helps in developing cleaner Java APIs.

11. What are the advantages of Optional?

Optional has the following advantages.

It helps in avoiding the null checks.
It is used for avoiding “NullPointerException”.

12. What is Type Inference in Java 8?

Type Interface refers to the compiler’s ability to determine the type of parameters when the method is called, i.e., at compile time.

13. What is the Default Method?

A default method adds functionality to an interface without breaking down the implementing class, and offers backwards compatibility.

14. Define Stream Pipelining.

Stream Pipelining in Java SE 8 is used for chaining operations together by splitting the operations that can happen on one stream. The two categories of Stream Pipelining are intermediate operations and terminal operations.

15. What is the compulsion in using Stream Pipeline?

The compulsion in using Stream Pipeline is the presence of a terminal operation which helps in returning the final value and supports termination of the pipeline.

16. Explain Predicate and Functions along with the code. What are the similarities?

Predicates and functions are both functional interfaces.

Predicate is a single argument function that gives the outcome as true or false. Its code is <T>.Function is a single argument function that gives outcomes in the form of an object. Its code is <T, R>.

17. What are the Core API classes for Java SE 8?

The Core API classes for Java SE 8 include LocalDate, LocalTime, and LocalDateTime.

18. What has replaced PermGen?

PermGen is used to store classes and has been replaced by MetaSpace in Java SE 8.

Advanced Java 8 Interview Questions

19. What is the functional interface?

The functional interface is the interface which carries only one abstract method. The code example below explains this further.

// Java program to demonstrate Implementation of

// functional interface using lambda expressions

class Test

{

 public static void main(String args[])

 {

// lambda expression to create the object

new Thread(()->

).start();

 }

}

20. Is there any difference between the Functional interface and SAM interface?

No, there is no difference between the functional interface and SAM interface. The SAM interface or Single Abstract Method interface is a kind of functional interface defined in the Java SE 8 API.

21. Can we define a functional interface? If yes, how?

Yes, we can define a functional interface. They can be defined using Java SE 8’s @Functionalinterface annotation to mark an interface as a functional interface.

22. What are the guidelines that are needed to be followed for Functional Interface?

There are several guidelines stated below which are needed to be followed for a functional interface. These are:

The interface should be defined with only one abstract method.
Not more than one abstract can be defined.
Making use of @Functionalinterface annotation in the interface definition.
The override of the Java.lang.object class’s method will not be considered as an abstract method.
Any method can be used for defining a number.

23. Which are the two most popular methods that can be used for defining any number in a Functional Interface?

The two most popular methods used for defining any number in a functional interface include static methods and default methods.

24. Is it mandatory to define a Functional Interface with @Functionalinterface annotation?

No. it is not mandatory to define a functional interface with @Functionalinterface annotation.

25. What is the compulsion in the Functional Interface definition?

The compulsion in the functional interface definition is when the Java Compiler forces us to use one abstract inside the interface.

26. What is the link between Lambda Expressions and Functional Interface?

Using Lambda Expressions means that we are using a functional interface - they are interrelated. The lambda expressions are a part of the functional interface, which is a bigger platform carrying various other features and expressions.

27. How is Collection API different from Stream API?

The difference between Collection API and Stream API are:

Collection API	Stream API
It is available since the introduction of Java 1.2	It is made available after the introduction of Java SE 8
It helps in storing Data which are set of objects.	It helps in computing data wherein computations of a set of data objects are made.
It can be used for storing a limited number of elements.	It can be used for storing an unlimited number of elements.
The construction of the Collection object is done Eagerly.	The construction of the Stream object is done Lazily.

28. How is Spliterator a different Iterator?

A Spliterator in Java SE 8 is an iterator interface. The following are the differences between the spliterator and iterator:

Spliterator	Iterator
It is introduced along with Java SE 8	It was introduced long ago with Java 1.2
It is defined as a Spliterator iterator.	It is defined as a non-spilterator Iterator.
It can be used in Stream API.	It can be used in Collection API.
It helps to iterate streams in parallel and sequential order.	It helps in iterate collections only in sequential order.
The examples include tryAdvance()	The examples include, next(), hasNext().

29. What are the common types of functional Interfaces in the standard library?

The common types of functional interfaces in the standard library include the following:

Predicate
Function
Consumer
Supplier
BiFunction
BinaryOperator
UnaryOperator

30. What is the major difference between Map and FlatMap stream operation?

The major difference between Map and FlatMap stream operation is that the former wraps its return value inside its ordinal type while the latter does not.

31. What is the similarity between Map and Flat map stream operation?

Both the Map and FlatMap stream operations are intermediate stream operations that receive a function and also apply these functions to different elements of the stream.

32. What is the advantage of Metaspace over PermGen?

PerGen was fixed in size and could not grow dynamically, while Metaspace can grow dynamically and does have any type of size constraint.

33. What are some examples of Intermediate Operations?

Examples of Intermediate Operations include the following.

Limit(long n)
skip (long n)
Distinct ()
Filter (Predicate)
Map (Function)

34. What are some examples of Terminal Operations?

Examples of terminal operations are:

Max
Min
AnyMatch
AllMatch
Reduce
ToArray
Count

35. Can we list the numbers and remove the duplicate elements in the list using Java SE 8 features?

Yes, we can list the numbers and remove the duplicate elements in the list by applying stream and then collecting it to set using Collections.toSet() method.

Conclusion

You just read some of the most popular Java 8 interview questions and answers. There’s a lot more to learn, but this is a good starting point. We hope these Java 8 interview questions help you get through that interview.

You can test your Java 8 skills further with this Udemy course focusing on Java 8 interview preparation. These will also help with Java 8 coding interview questions and core Java 8 interview questions.

You should also consider reading Coding Interview Questions to prepare common questions pertaining to a coding background.

If you have any questions or suggestions, feel free to drop a comment below.

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Java SE 8 is the latest Java language ......still in 2020

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What Is Nashorn in Java8?

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Explain the Syntax and Characteristics of a Lambda Expression What Is Nashorn in Java8?

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What Is the Meaning of String::Valueof Expression?

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What Is a Method Reference?

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Difference between Stream’s findFirst() and findAny()?

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findAny() method finds the first element in the stream. You can use it whenever you want to search the first element from any sequence.

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Given the list of numbers, remove the duplicate elements from the list.

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Can you provide some APIs of Java 8 Date and Time?

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Java 8 introduced new date and time API’s to overcome the shortcomings of the older java.util.date and java.util.calender. There are two date-time APIs that fall under package java.time that are Local and Zoned.

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What are the defaults methods?

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Earlier interfaces have abstract methods only and the implementation is given in separate class. If we want to add a new method in an interface then the code has to be provided in the class that implements the same interface. To overcome this issue the concept of default methods come to light. It allows the interface to have new methods without impacting the classes that implement the interface.

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