Java is a widely used programming language for various types of development projects, from the web and Android apps to the Internet of Things (IoT). As per research, Java was among the most popular job posting languages in 2019. Given its pervasiveness, it’s no wonder that experts who are fluent in Java remain in high demand.
That is why we have compiled a list of the most popular Java 8 interview questions and answers. But, it is not enough to have considerable expertise and knowledge in a certain field. People must organize ideas, study the relevant facts, and concentrate on the most often-asked questions.
So, first of all, let’s begin with the basics of Java 8; we will move to the Java 8 interview questions for experienced and freshers.
What Is Java 8?
Java 8 is a major release of the Java programming language that was first released in March 2014. It introduced several new features and improvements, including adding lambda expressions and functional interfaces, a new date/time API, and improvements to the Streams API.
It introduced the concept of default methods, which allow interfaces to have method implementations, and the optional class, which is used to represent nullable values. Java 8 was the first version of Java to include support for functional programming concepts.
So, this is all about Java 8. Now let’s move to the Java 8 interview questions and answers for experienced professionals.
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Top Java 8 Interview Questions and Answers
Are you preparing to crack the Java 8 interview in 2024? If yes, then this article is for you. Here is the list of the most popular interview questions on Java 8 that will help you easily ace the interview process.
1. What are the new features introduced in Java 8?
It is one of the most asked Java 8 features interview questions. Because Java 8 was a major release and introduced several new features, including Lambda expressions, stream API, default methods, concurrent accumulators, and more.
Let’s talk about these here:
a) Lambda Expressions
A new way to represent functional interfaces, which are interfaces with a single abstract method.
b) Method References
A shorthand for lambda expressions that refer to a method.
c) Stream API
A unique way to process data collections allows for operations like filtering, mapping, and reducing to be performed more efficiently and expressively.
d) Default Methods
A way to add new methods to existing interfaces without breaking existing code that implements those interfaces.
e) Optional class
A new class for representing optional values can be used to avoid null pointer exceptions.
f) Date and Time API
A new package, java.time, was introduced in Java 8, which provides classes to represent date-time, duration, time, instant, and timezone.
g) Nashorn JavaScript Engine
A new high-performance JavaScript engine was introduced to replace the existing Rhino engine.
h) Concurrent Accumulators:
A new package, ava.util.concurrent.atomic, was introduced, which provides classes for atomic variables, arrays, and updater.
2. What is Lambda Expression in Java 8?
The lambda expression was introduced in Java 8 to offer users an anonymous function that can be invoked without specifying a function name. It has a functional set of parameters with a lambda entity.
A lambda expression has the following structure:
(Argument List) ->{expression;} or
(Argument List) ->{statements;}
It is one of the most asked Java 8 questions during an interview, so whether you are a fresher or experienced, you should know it.
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3. What are the benefits of Java SE 8?
The advent of Java SE 8 has proven tremendously beneficial to programmers in various ways. They are as follows:
- It makes the code shorter and easier to understand. Java SE 8’s functional interfaces and Lambda expressions make the code more reusable.
- It is useful for developing parallel programs.
- Java made it simple to write database-like operations.
- It improves the performance of several apps.
- Java aids in the creation of exceptional interfaces and highly scalable programs.
- In Java SE 8, code may be made more productive.
- Compared to prior versions, programming in Java 8 can be maintained and tested more rapidly.
It is one of the most commonly asked Java 8 interview questions for 10 years of experience or intermediate-level programmers.
4. Can you develop a custom functional interface with Java 8?
Yes, Java 8 allows you to create a custom functional interface.
The following example shows how to create an interface called ‘CustInterface’:
package org.arpit.java2blog;
public interface CustInterface{
void print();
default void printColor()
{
System.out.println("Printing the color");
}
}The main class can be created like this:
package org.arpit.java2blog.constructor;
public class FunctionalIntefaceMain {
public static void main(String[] args)
{
FunctionalIntefaceMain pMain=new FunctionalIntefaceMain();
pMain.printForm(() -> System.out.println("Printing form"));
}
public void printForm(CustInterface c)
{
c.print();
}
}When the application starts, it displays the message “printing form” on the screen. It is critical that you learn Java through the programming method.
5. What are the core Date and Time API Classes in Java 8?
Another popular interview questions on Java 8 include concepts like data and time API classes. You must know that there are three primary core API classes for date and time, as listed below:
- LocalDate
- LocalTime
- LocalDateTime
6. What is Nashorn in Java 8?
Nashorn is a new JavaScript processing engine that was included with Java 8. It adheres to ECMA JavaScript requirements more closely and outperforms its predecessor, Rhino, in runtime performance. It is one of the top Java 8 interview questions for 10 years of experience.
7. What are the benefits of Metaspace over Permgen?
PerGen had a set size and could not grow dynamically, but Metaspace can grow dynamically and has no size constraints.
8. What is MetaSpace in Java 8? How does it differ from PermGen?
It is one of the most often asked Java 8 interview questions and answers candidates must be aware of.
– PremGen
Before Java 8, class metadata was kept in the PremGen (Permanent-Generation) memory type. It has a fixed size and cannot be resized dynamically. It was a single Java Heap Memory.
– MetaSpace
Java 8’s ‘MetaSpace’ native memory storage for class MetaData. Because it is not a contiguous Heap Memory, it may be created dynamically, which aids in overcoming size limits. It improves trash collection, auto-tuning, and metadata de-allocation.
9. What are some Standard Java Pre-Defined Functional Interfaces?
In Java, several pre-defined functional interfaces exist in the java.util.function package, including:
a) Predicate<T>
Represents a boolean-valued function of one argument.
b) Consumer<T>
Represents an operation that accepts a single input argument and returns no result.
c) Function<T, R>
Represents a function that takes one argument and returns a result.
d) Supplier<T>
Represents a supplier of results.
e) UnaryOperator<T>
Represents an operation on a single operand that produces a result of the same type as its operand.
f) BinaryOperator<T>
Represents an operation upon two operands of the same type, producing a result of the same type as the operands.
Additionally, the java.util.comparator is also a functional interface.
10. What is a Default Method in Java 8, and why is it required?
The default method is a method in the interface with a predetermined body. It makes use of the term default. In Java 8, default methods were provided to ensure ‘Backward Compatibility so that the JDK alters any interfaces.
If a new abstract method is added to the interface, all classes that implement the interface will be broken and must implement the new method. The interface implementing classes will be unaffected by default methods.
If necessary, default methods can be overridden in the implementation. Furthermore, it is not synchronized or final. It is another common concept in our list of top interview questions on java 8 for experienced.\
11. Why was Java 8 introduced?
Java 8 was introduced to bring new features and enhancements to the Java programming language and its platform. The main objectives of Java 8 were to make the language more functional, improve developer productivity, and increase performance.
Some of the key features introduced in Java 8 include:
- Lambda expressions, which allow developers to write code in a functional programming style, making it more concise and readable.
- Stream API provides a powerful and efficient way to process collections of data.
- The Optional class provides a better way to handle null values and reduce the likelihood of NullPointerExceptions.
- New Date and Time APIs, provide a much-needed improvement to the previous Date and Time classes.
- Method references, which allow developers to reference existing methods as if they were lambda expressions.
These and other enhancements in Java 8 have made the language more powerful, easier to use, and better suited to modern programming challenges.
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12. When was Java 8 released?
Java 8 was released in March 2014.
13. Are Java 8 streams lazy?
Yes, Java 8 streams are lazy by default. Lazy evaluation means that a stream’s operations are not executed until a terminal operation is invoked on the stream. This allows intermediate operations on the stream to be optimized and executed more efficiently.
For example, if you have a stream of numbers and you apply a filter operation to select only even numbers, the filter operation will not actually be executed until a terminal operation like forEach or count is invoked on the stream. This allows the stream to skip over elements that do not match the filter criteria, improving performance.
It is also possible to make intermediate operations in a stream eager, or immediate, by using the eager evaluation operator, like forEachOrdered, to the stream.
14. What are Collectors in Java 8?
Well, Java 8 stream interview questions are majorly asked by the interviewers, so you should know this.
In Java 8, collectors are classes that implement the Collector interface and provide methods for accumulating elements into a container, such as a List or Set. They are used in conjunction with the Stream API to perform various types of collection and reduction operations, such as grouping, counting, and averaging elements in a stream.
Examples of built-in collectors in Java 8 include Collectors.toList(), Collectors.toSet(), and Collectors.groupingBy().
15. When should we use the Stream API in Java 8?
The Stream API in Java 8 may be utilized efficiently if your Java project requires the following operations:
- Execute database operations
- Lazily carry out operations
- Make use of internal iteration
- Execute parallel processing
- Write functional programming
- Make use of pipeline activities
16. What is the difference between Map and Flatmap stream operations?
The primary difference between Map and FlatMap stream operations is that the former wraps its return value within its ordinal type, while the latter does not.
17. How to print the date of the next Wednesday in Java 8?
The following code prints the next Wednesday date that occurs in the calendar:
/Print the next Wednesday that occurs.
LocalDate today = LocalDate.now();
LocalDate nextWednesday =
today.with(TemporalAdjusters.next(DayOfWeek.WEDNESDAY));
System.out.println("Next Wednesday on : "+ nextWednesday);18. What is the difference between Map and Flat Map stream operations in Java 8?
The Map and FlatMap stream operations are both intermediate stream operations that take a function and apply it to distinct parts of the stream.
19. In Java 8, what is the purpose of the optional keyword?
In Java 8, the optional keyword is used to prevent the occurrence of the NullPointerException. The empty() static function, as demonstrated below, makes it simple to build an optional object:
@Test
public void whenCreatesEmptyOptional_thenCorrect() {
Optional<String> empty = Optional.empty();
assertFalse(empty.isPresent());
}20. What is the basic structure/syntax of a Lambda expression?
FunctionalInterface fi = (String name) -> {
System.out.println(“Hello “+name);
return “Hello “+name;
}
The lambda expression is separated into three different pieces, as shown below:
- Arguments/Parameters List:
In () round brackets, a list of parameters is passed. It can contain 0 or more parameters. The type of argument is optional and can be deduced based on the context.
- Token of the Arrow:
The lambda arrow operator is known as the arrow token. It is used to divide the parameters from the body or points to the body from the list of arguments.
- Body/Expression:
Expressions and assertions can be found in the body. Curly braces are only necessary when there are many lines. The return type in one statement is the same as the statement. In other circumstances, the return type is implied by the return keyword, or it is void if nothing is returned.
It is another one of the most popular and advanced Java 8 interview questions for 12-year experienced candidates. So, experienced ones should know the answer to this question.
21. What is an optional class in Java 8?
Optional is a container type that may or may not contain a value, such as null or not null. It is included in java.util package. There are built-in methods such as isPresent(), which returns true if the value is present or false otherwise, and get(), which returns the item if it is present.
static Optional<String> changeCase(String word) {
if (name != null && word.startsWith("A")) {
return Optional.of(word.toUpperCase());
}
else {
return Optional.ofNullable(word); // someString can be null
}
}Students or experienced in preparing for Java 8 interview questions and answers should be well-versed in this.
Interview Questions for You to Prepare for Jobs
22. What Are Java 8 Streams?
Java 8 stream interview questions are also majorly asked by recruiters. Well, a stream is a declarative concept for expressing data processing requests. It is a data pipeline not connected to Java I/O Streams and represents a succession of data objects and a series of operations on that data.
The most important interface is java.util.stream.Stream<T>. It takes Functional Interfaces, which allow lambdas to be passed. Streams provide a fluid interface or chaining.
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23. What is a consumer in Java 8?
A consumer, like a predicate, is a single argument functional interface in Java 8. On the other hand, the consumer does not return any value and may be used for lambda expressions.
The following sample code shows how to use the consumer interface to output a string:
import java.util.function.Consumer;
public class Java8ConsumerExample {
public static void main(String[] args) {
Consumer<String> consumerString=s->System.out.println(s);
consumerString.accept("HelloWorld");
}
}24. What is a supplier in Java 8?
In Java 8, a supplier is a primary functional interface that does not accept any arguments. When using lambda expressions, it is utilized as an assignment target.
The following is an example of how a supplier is used:
import java.util.function.Supplier;
public class Java8SupplierExample {
public static void main(String[] args) {
Supplier<String> supplier= ()-> "HelloLearners";
System.out.println(supplier.get());
}
}25. What does the peek() function in Java 8 do?
In Java 8, the peek() method is part of the stream class and is used to examine activities conducted through a stream pipeline. Peeking may be done at any time to output messages about the code being run to the console.
Peeking is useful when performance is required while debugging code using the lambda expression or when conducting stream processing.
26. What is the difference between intermediate and terminal operations in Java 8?
Intermediate Operations
- The stream items must be processed
- Typically, it converts one stream into another
- Internal iteration of all source items is performed
- The operations are carried out in the sequence specified
- The majority of intermediate operations are lambda functions
Terminal Operations
Starts the Stream pipeline, which is then used to gather the processed Stream data.
int count = Stream.of(1, 2, 3, 4, 5)
.filter(i -> i <4) // Intermediate Operation filter
.count(); // Terminal Operation count27. Which intermediate operations are most typically used in Java 8?
It is one of the top Java 8 interview questions and answers that candidates should know while appearing in an interview.
a) Filter(PredicateT>)
Enables the processing of Stream items selectively. It returns items that fulfil the predicate’s provided condition.
b) map(FunctionT, R>)
Returns a new Stream after converting each element with the specified mapper function.
c) = sorted()
Sorts the input components before moving them on to the next stage.
d) distinct()
Only pass elements to the next step that have not yet been passed.
e) limit(long maxsize)
Sets the maximum stream size to maxsize.
f) skip(long start)
Skip the first components till the end.
g) peek(Consumer)
Apply a consumer to the stream without modifying it.
h) flatMap(mapper)
Convert each element to a stream of its component elements and combine all streams into a single stream.
28. Which are the most common terminal operations in Java 8?
These are the primary types of terminal operations:
a) collect()
Retrieves a single result from the stream sequence’s elements.
b) reduce()
Generates a single result from all stream sequence items.
- count() – This function returns the number of entries in the stream.
- min() – Returns the stream’s minimum element.
- max() – Returns the stream’s maximum element.
c) Search/Query Operations
- anyMatch(), noneMatch(), allMatch(),… are search/query procedures. – Operations involving short-circuiting.
- For the match condition, it accepts a Predicate as input.
- Stream processing will be terminated as soon as the outcome is known
d) Iterative Operations forEach()
Useful for doing something with each member of the Stream. It accepts customers.
e) forEachOrdered()
This function is useful for keeping order in concurrent streams.
In addition to these, you must also go through the common Java interview questions and answers so that you have good command.
Java 8 Interview Questions for 10 Years Experience
Here are some advanced Java 8 interview questions for 10+ years experienced candidate:
- Can you explain the use of parallel Streams in Java 8 and their performance implications?
- Can you discuss the limitations and trade-offs of using parallel Streams in Java 8?
- How do you handle exceptions while using Java 8 Streams?
- Can you provide an example of how to use the collect operation to group elements in a Stream in Java 8?
- Can you explain the use of the flatMap operation in Java 8 Streams for flattening collections?
- How do you handle infinite Streams in Java 8?
- Can you discuss the performance differences between sequential and parallel Streams in Java 8?
- Can you explain the use of the partitioning collector in Java 8 Streams?
- Can you discuss the difference between reduce and collect operations in Java 8 Streams?
- Can you show an example of using the mapToInt, mapToLong, and mapToDouble operations in Java 8 Streams?
- Can you explain the use of the toArray operation in Java 8 Streams and its performance implications?
- Can you explain the use of the anyMatch, allMatch, and noneMatch operations in Java 8 Streams?
These are some of the more advanced questions related to Java 8 and are suitable for a candidate with 10+ years of experience.
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Java 8 Interview Questions for 12 Years Experience
Here are some advanced Java 8 interview questions for a 12+ years experienced candidate:
- How do you ensure thread safety while using parallel Streams in Java 8?
- Can you discuss the limitations and trade-offs of using parallel Streams in Java 8?
- What are the common performance optimization techniques while using Streams in Java 8?
- How do you handle exceptions while using Java 8 Streams?
- Can you provide an example of how to use the collect operation to group elements in a Stream in Java 8?
- Can you explain the use of the flatMap operation in Java 8 Streams for flattening collections?
- How do you handle infinite Streams in Java 8?
- Can you discuss the performance differences between sequential and parallel Streams in Java 8?
- Can you explain the use of the partitioning collector in Java 8 Streams?
- Can you discuss the difference between reduce and collect operations in Java 8 Streams?
- Can you show an example of using the mapToInt, mapToLong, and mapToDouble operations in Java 8 Streams?
- Can you discuss the use of the toArray operation in Java 8 Streams and its performance implications?
- Can you explain the use of the anyMatch, allMatch, and noneMatch operations in Java 8 Streams?
These are some of the more advanced questions related to Java 8 and are suitable for a candidate with 12+ years of experience.
Java 8 Stream Interview Questions
Here are some common Java 8 Stream interview questions:
- What is a Stream in Java 8, and how is it different from a Collection?
- How do you create a Stream in Java 8?
- What are the intermediate operations in Java 8 Stream API?
- What are the terminal operations in Java 8 Stream API?
- Can you explain the difference between map and flatMap in Java 8 Streams?
- What is the use of Optional in Java 8 Streams?
- Can you provide an example of how to use parallel Streams in Java 8?
- What are the different ways to create a Stream in Java 8?
- Can you explain the difference between reduce and collect in Java 8 Streams?
- Can you show how to use the filter operation in Java 8 Streams?
- How do you sort a Stream in Java 8?
- Can you show how to use the groupBy operation in Java 8 Streams?
- Can you explain the difference between Stream and Sequence in Java 8?
- Can you show an example of using the min and max operations in Java 8 Streams?
- These are some of the popular questions related to Java 8 Streams.
Java 8 Features Interview Questions
Here are some common Java 8 features interview questions:
- What is the biggest feature added in Java 8?
- Can you explain the concept of Lambda expressions in Java 8?
- What is a functional interface in Java 8, and how is it used?
- How do the default and static methods in interfaces work in Java 8?
- Can you provide an example of how to use the Stream API in Java 8?
- Can you explain the difference between forEach and forEachOrdered in Java 8 Streams?
- How does the Optional class in Java 8 help to prevent NullPointerException?
- What are the new Date and Time APIs introduced in Java 8?
- Can you explain the difference between the old java.util.Date and java.time.* classes in Java 8?
- Can you show an example of using the new Date and Time APIs in Java 8?
- Can you explain the use of Method reference in Java 8?
- How does Java 8 support parallel processing in Streams?
- Can you show an example of using the filter, map, and reduce operations in Java 8 Streams?
- What are the new additions in Java 8 related to the java.util.function package?
These are some of the popular questions related to Java 8 features.
Java 8 Programs for Interview
The specific Java 8 programs that are asked in job interviews can vary depending on the company and the role you are applying for. However, here are some common Java 8 topics and programs that are commonly asked in job interviews:
- Lambda expressions: Write simple and complex examples of using lambda expressions to simplify code.
- Stream API: Write examples of using the Stream API to process collections of data, such as filtering, mapping, reducing, and grouping elements.
- Optional: Write examples of using the Optional class to handle null values and reduce the likelihood of NullPointerExceptions.
- Date and Time API: Write examples of using the new Date and Time APIs in Java 8 to handle dates and times in a more efficient and user-friendly way.
- Method references: Write examples of using method references to simplify code and make it more readable.
- Function composition: Write examples of composing functions in a functional programming style.
- Parallel streams: Write examples of using parallel streams to improve performance and write multi-threaded code.
These are some of the common topics and programs that are often asked in job interviews for Java 8. It’s important to be familiar with the basics of these topics and be able to write code snippets to demonstrate your understanding.
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Conclusion!
This is the list of the top 25 Java 8 interview questions and answers that are very likely to be asked in 2024 and beyond. Now that you have a list of the popular questions of Java 8, it is time to prepare for them and ace your interview like a pro.
For better preparation and professional assistance, you can go for a reliable Java programming course with a certificate.
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