Top Java 8 Interview Questions & Answers in 2020

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Top Java 8 Interview Questions & Answers in 2020

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Java has been well known for adding various new features from time to time. Java 8 SE is the new release of Java programming language development project. It was released on 18th March 2014 with the view to overcome the loopholes and drawbacks of earlier versions of Java and upgrade it will add features and characteristics. Java 8 SE has been developed with the purpose to add a functional programming facility, create a new JavaScript search engine, manipulate the date-time with new APIs and deploy new streaming API.

Top Java 8 Interview Questions and Answers

Although the additions made in Java 8 SE add to the knowledge of the person, however, for those who are not aware or miss the opportunity to learn about the latest additions can go through the following top 50 Java 8 interview questions and answers in 2020.

Question: Which company has developed Java?

Answer: Oracle Corporation had introduced Java and is keeping on updating the versions with added features and benefits to the users.

Question: Which is the latest Java language?

Answer: Java SE 8 is the latest Java language that has distinct and highly useful features and concepts that could help computer programmers.

Question: Do we need changes and reforms in Java?

Answer: Yes, we do need changes and reforms in Java language because of the following reasons.

  1. To make the best and efficient use of multi-million CPUs that are deployed at work throughout the world.
  2. To meet with the changes and up-gradation made in the technology hardware and software.
  3. To support the running of various kinds of applications.
  4. To create highly concurrent and scalable applications.
  5. To make use of all the functional programming features which are an integral part of the latest Java SE 8 computer language.

Answer: The most popular and well-known latest features of Java SE 8 include the following.

  1. Functional Interfaces.
  2. Collections API Enhancements.
  3. Lambda Expressions.
  4. Spliterator.
  5. Stream API and more.

Question: What makes Java SE 8 superior over others?

Answer: Java SE 8 has the following features that make it superior over others.

  1. It writes the parallel code.
  2. It offers even more useable codes.
  3. It has improved performance applications.
  4. It has more readable and concise codes.
  5. It supports writing database including promotions.

Question: Define a Lambda Expression in Java SE 8?

Answer: A Lambda Expression is Java SE 8 is a name given to an anonymous function that helps in accepting a different set of inputs parameters and offers a variety of results outcomes.

Question: Why is Lambda Expression coined as a block of code?

Answer: Lambda Expression is coined as a block of code because it has no name and can be with or without the parameters and results.

Question: What is the distinct feature of the Block of Code?

Answer: A Block of Code has the distinct feature of getting executed on only demand.

Question: Define the different parts of Lambda Expression?

Answer: There are three different parts of Lambda Expression which include the following.

  1. Parameter List.
  2. Lambda Body Expression.
  3. Lambda Arrow Operator.

Question: How is the Parameter List of Lambda Expression different from the Lambda Arrow Operator?

Answer: Lambda Expression can carry zero, one or even more parameters at one time. On the other hand, the Lambda Arrow Operator separates these parameters from the list and body using the icon "->".

Question: What are the distinct features of Lambda Expression?

Answer: The distinct features of Lambda Expression include the following.

  1. It has no specific parameters.
  2. It returns any results.
  3. Its type is “Java.lang.Runnable”.

Question: How is Lambda Expression highly useful?

Answer: Lambda Expression is highly useful because it offers a functional interface.

Question: Define the functional interface?

Answer: The functional interface is referred to as the interface which carries only one abstract method. The code example can be used for explaining the functional interface.

// 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(()->

New thread created

Question: Is there any difference between the Functional interface and SAM interface?

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

Question: Can we define our functional interface? If yes, how?

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

Question: What are the guidelines that are needed to be followed in Functional Interface?

Answer: There are several guidelines stated below which are needed to be followed in Functional Interface.

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

Answer: The two most popular methods used for defining any number in a Functional Interface include Static methods and Default methods.

Question: Is it mandatory to define a Functional Interface with @Functionalinterface annotation?

Answer: Not it is not mandatory to define a Functional Interface with @Functionalinterface annotation in case we don’t want it and hence omitting this annotation can be followed.

Question: What is the compulsion in the Functional Interface definition?

Answer: The compulsion in the functional interface definition is that the Java Compiler forces to make use of one abstract inside the interface.

Answer: When we are using Lambda Expressions then that means that we are using a Functional interface. Therefore they are both interrelated. This means that Lambda Expressions are a part of the Functional interface which is a bigger platform carrying various other features and expressions.

Question: How is Collection API different from Stream API?

Answer: The difference between Collection API and Stream API can be stated as under.

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.

Question: Define a Spliterator in Java SE 8?

Answer: A Spliterator in Java SE 8 is one of the latest iterator interface introduced by Oracle Corporation as part of Java SE 8.

Question: How is Spliterator a different Iterator?

Answer: The following are the differences between 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().

Question: Define Optional in Java SE 8?

Answer: Optional is defined as a final class that is introduced as an integral part of Java SE8. It is a java. util package.

Question: What is the use of Optional in Java SE 8?

Answer: 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.

Question: How many values can Optional have in Java SE 8?

Answer: Optional in Java SE 8 can have either one value or zero value.

Question: What are the advantages of Optional?

Answer: Optional has the following advantages.

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

Question: Define Type Inference in Java SE 8?

Answer: Type Interface in Java SE 8 is referred to as determining the Type by the compiler at the compile time.

Question: Was Type Inference available before Java SE 8?

Answer: Yes, Type Inference was available before Java SE 8 in Java 7 and even earlier Java languages.

Question: What are the common types of Functional Interfaces in the Standard Library?

Answer: The common types of Functional Interfaces in the Standard Library include the following.

  1. Predicate
  2. Function
  3. Consumer
  4. Supplier
  5. BiFunction
  6. BinaryOperator
  7. UnaryOperator

Question: What is the Default Method?

Answer: A Default Method is found in an interface and can be used for the implementation purpose of new functionality added to the interface.

Question: Define Nashorn in Java SE 8?

Answer: Nashorn is the latest Javascript processing engine that is used on the Java platform of Java SE 8. 

Question: What was used as a Javascript processing engine before Java SE 8?

Answer: Earlier to Nashorn, Mozilla Rhino was used as a Javascript processing engine.

Question: What is the use of the JJS command-line tool?

Answer: JSS is the latest executable command-line tool in Java SE 8 which helps in executing the Javascript code at the console.

Question: What is the major difference between Map and FlatMap stream operation?

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

Question: What is the similarity between Map and Flat map stream operation?

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

Question: Define Stream Pipelining?

Answer: Stream Pipelining in Java SE 8 is used for chaining operations together by splitting the operations that can happen on one stream.

Question: What are the two categories of Stream Pipelining?

Answer: The two categories of Stream Pipelining are Intermediate operations and Terminal operations.

Question: What is compulsion in using Stream Pipeline?

Answer: 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.

Question: What is the role of the New Date and Time API?

Answer: New Date and Time API is designed in Java SE 8 under the package java time so that the problems and issues related to JDK or can be avoided.

Question: Can we create our functional interface?

Answer: Yes, we can create our functional interface by using the code “Printable”.

Question: Define Predicate? Display its Code?

Answer: Predicate is a single argument function that gives the outcome as true or false. Its code is <T>.

Question: Define Function? Display its Code?

Answer: Function is a single argument function that gives outcomes in the form of an object. Its code is <T, R>.

Question: What are the similarities between Predicate and Function?

Answer: Predicate and Function are both functional interfaces.

Question: What are the Core API classes for Java SE 8?

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

Question: Define PermGen? What is its current status?

Answer: PermGen is used to store classes. It has been removed in Java SE 8 and has been replaced with MetaSpace.

Question: What is the advantage of Metaspace over PermGen?

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

Question: What are the examples of Intermediate Operations?

Answer: Examples of Intermediate Operations include the following.

  1. Limit(long n)
  2. skip (long n)
  3. Distinct ()
  4. Filter (Predicate)
  5. Map (Function)

Question: What are the examples of Terminal Operations?

Answer: The examples of Terminal Operations are as follows.

  1. Max.
  2. Min.
  3. AnyMatch.
  4. AllMatch.
  5. Reduce.
  6. ToArray.
  7. Count.

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

Answer: 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.


The above are the most popular java 8 interview questions and answers that are asked in Java SE 8 interviews. We hope our assembling of these java 8 interview questions helps in the successful cracking of the Java SE 8 interview.

Test your Java 8 skills further with this Udemy course focusing on Java 8 Interview Preparation.

Not feeling confident with the above-mentioned questions and still facing difficulties? Consider reading Coding Interview Questions to prepare common questions pertaining to a coding background.

If you have any questions or queries or suggestions then feel free to reply in the comment box.

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Davinder Pal Singh

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Question: Which company has developed Java?
Answer: Oracle Corporation had introduced Java

this is wrong.

Norma Stewart
Norma Stewart

What Is Nashorn in Java8?

Teresa Gill
Teresa Gill

Nashorn is a much-improved JavaScript engine that replaces the existing Rhino. Nashorn provides better performance and directly compiles the code in memory that passes the bytecode to the JVM. Nashorn uses the invoke dynamics feature that was introduced in Java 7 to improve performance.

Brent Lyons
Brent Lyons

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

Elaine Palmer
Elaine Palmer

Lambda syntax-
(Object arg1, int arg2) -> arg1.equals(arg2);
Lambda syntax consists of three parts- a list of parameters, an arrow and a body. Following are the characteristics of the lambda expression.
No need to declare the type of parameter explicitly as the compiler can inference the same from the value of the parameter.
You can avoid parenthesis for single parameter and can use for multiple parameters.
Can avoid braces in expression body if there is a single statement.
Curly braces are used to indicate that expression will return a value which can be avoided for a single statement.

Billie Ballard
Billie Ballard

What Is the Meaning of String::Valueof Expression?

Katherine Gibbs
Katherine Gibbs

Java string valueof() method is used to create a string representation from a different type of inputs and accept the following type of arguments-
char array

Clay Butler
Clay Butler

What Is a Method Reference?

Gertrude Ramsey
Gertrude Ramsey

Method reference is introduced with Java 8. It is a shorthand notation of lambda expression to call a method. For example
Lambda expression-
Str -> system.out.println(str)
Method reference-

Alejandro Robertson
Alejandro Robertson

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

Gerald Thompson
Gerald Thompson

There are two methods that are introduced with Java 8- findFirst() and findAny().
findFirst() method is used to find any element from the stream. You can use it whenever you are searching for an element without paying attention to the encounter order.
findAny() method finds the first element in the stream. You can use it whenever you want to search the first element from any sequence.

Jill Mccormick
Jill Mccormick

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

Lisa Lee
Lisa Lee

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

Warren Gibbs
Warren Gibbs

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

Jerald Dixon
Jerald Dixon

What are the defaults methods?

Madeline Parker
Madeline Parker

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.

Lora Daniel
Lora Daniel

What is the method reference in java 8?

Aaron Ramirez
Aaron Ramirez

Java 8 comes with a new feature called method reference which is used to refer methods of functional interface. It is an easy and compact form of the lambda expression. Whenever you use a lambda expression to refer a method, you can replace the lambda expression with method reference.