Top 40+ Java 8 Interview Questions With Answers

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Nervous about your upcoming Java 8 interview? Don’t worry; our guide is here to help! Did you know? Over 50% of Java developers use Java 8. This highlights the importance of knowing Java 8 features and concepts when preparing for an interview. To help you succeed, we’ve compiled a list of the top 40+ Java 8 interview questions, along with detailed answers. These interview questions on Java 8 will boost your knowledge and confidence.

Get ready to impress your interviewer!

Java 8 Interview Questions for Freshers

Here are the most common Java 8 interview questions and answers for freshers. 

1. What is Java 8?

Java 8 is a major update to the Java programming language, released in March 2014. It includes new features like lambda expressions, the Stream API, and the new Date and Time API.

2. Can you explain lambda expressions in Java 8?

This is one of the most common lambda expression interview questions you may encounter. 

Lambda expressions are a way to write anonymous functions. They let you pass code as data, which makes your code more concise and easier to read. 

For example:

(int a, int b) -> a + b

3. Why was the Optional class introduced in Java 8?

You may also come across an Optional class in Java 8 interview questions like this one. 

The Optional class is used to represent a value that might be present or absent. It helps avoid null pointer exceptions by providing methods to check for and handle the absence of a value in a more controlled manner.

4. What is the new Date and Time API in Java 8?

The new Date and Time API in Java 8, found in the java.time package is a comprehensive set of classes for handling dates and times. It is designed to be more intuitive and less error-prone than the old java.util.Date and java.util.Calendar classes.

5. What is the purpose of method references in Java 8?

Method references provide a way to refer to methods without invoking them. They make your code more readable and concise. Method references can be used to point to static methods, instance methods, or constructors.

6. How does Java 8 handle concurrency improvements?

Java 8 introduced the java.util.concurrent package, which includes new classes like CompletableFuture to help manage asynchronous programming. These classes simplify writing concurrent code by providing more flexible and powerful ways to handle tasks.

These are the most basic interview questions on Java 8 that you may encounter as a fresher. 

Java 8 Features Interview Questions

You may also come across these Java 8 new features interview questions. 

7. What is a functional interface, and how is it used in Java 8?

A functional interface is an interface with exactly one abstract method. It can be used with lambda expressions and method references. Functional interfaces provide target types for lambda expressions, making the code cleaner and more concise.

8. How do you use the forEach method in Java 8?

The forEach method is a new addition in Java 8 that is used to iterate over elements in a collection. It is a default method in the Iterable interface and can accept a lambda expression to perform an action for each element.

9. What are collectors in Java 8?

Collectors are a part of the Stream API that allows you to gather the elements of a stream into various forms, such as lists, sets, or maps. The Collectors utility class provides several predefined collectors for common operations like grouping, partitioning, and joining elements.

10. What are the new features in the java.util.function package?

The java.util.function package in Java 8 includes functional interfaces like Predicate, Function, Supplier, and Consumer. These interfaces are used to define lambda expressions and method references, making it easier to write functional-style code.

Java 8 Interview Questions for Experienced 

Here are some important Java 8 interview questions and answers for experienced candidates. 

11. What is Java 8 StringJoiner class used for?

Java 8 StringJoiner class is used to construct a sequence of characters separated by a delimiter. It helps in joining multiple strings with a specified delimiter and optionally with a prefix and suffix.

12. What is jjs in Java 8?

jjs is a command-line tool in Java 8 that is used to invoke the Nashorn JavaScript Engine. It allows you to run JavaScript code directly from the command line.

13. What is Nashorn, and what are its advantages?

This is one of the most common Java 8 interview questions for 5 years experienced candidates. 

Nashorn is a JavaScript engine introduced in Java 8. It provides advantages such as improved performance and better compliance with the ECMAScript standard. Nashorn allows seamless integration of JavaScript code with Java applications.

Also Read - Top 25+ JavaScript Interview Questions and Answers

14. What are the key features of Java 8 that have significantly impacted Java programming?

This is one of the most important core Java interview questions for 8-year experienced candidates. 

Java 8 introduced significant features like lambda expressions, the Stream API, default methods in interfaces, the new Date and Time API, Optional class, method references, and functional interfaces, all of which have transformed Java programming.

15. What’s the difference between findFirst() and findAny()?

This is one of the most common Java interview questions for 8-year experienced candidates. 

In Java 8 Streams, the findFirst() method returns the first element of the stream, while the findAny() method returns any element of the stream. 

The difference between them is more noticeable in parallel streams, where findFirst() returns the first element in the encounter order, whereas findAny() returns any element without considering the encounter order.

16. How has Java 8 changed your way of writing code?

You may also come across Java 8 interview questions for 10 years experienced candidates like this one.

“Java 8 has significantly improved my coding style. With features like lambda expressions and the Stream API, I can write code more concisely and expressively. It has made my development process smoother and more efficient.”

Also Read - Job Experience Letter Format and Samples

Java 8 Stream API Interview Questions

Here are some common Stream API in java 8 interview questions and their answers. 

17. What is the Java 8 Stream API?

This is one of the most common Stream API interview questions. 

The Java 8 Stream API is a powerful tool for processing collections of data in a functional programming style. It allows you to perform operations like filtering, mapping, and reducing on a sequence of elements.

18. How do you create a Stream in Java 8?

The interviewer may also ask you Java stream programming questions like this one. 

You can create a Stream in Java 8 using the stream() method on collections or the of() method in the Stream interface. 

For example:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);

Stream<Integer> stream = numbers.stream();

19. What are the intermediate operations in Java 8 Stream API?

Intermediate operations in the Stream API include filter(), map(), sorted(), distinct(), limit(), and skip(). These operations are used to transform and filter the elements of a stream.

20. What is the terminal operation in Java 8 Stream API?

The terminal operation in the Stream API triggers the processing of elements and produces a result. Examples of terminal operations include forEach(), collect(), reduce(), count(), and anyMatch().

Also Read - Top 20+ Java Collections Interview Questions With Answers

Lambda Expression Interview Questions In Java

Now, let’s take a look at a few Lambda Expression interview questions in Java and their answers:

21. What are the benefits of using lambda expressions in Java?

Lambda expressions in Java improve code readability and reduce boilerplate code by allowing developers to write more concise and functional-style code. They enable the use of anonymous functions, making it easier to implement functional interfaces and pass behavior as arguments.

22. Can lambda expressions access variables outside their scope?

Yes, lambda expressions can access final or effectively final variables from the enclosing scope. These are variables that are either declared as final or have not been reassigned after their initial assignment.

23. How does a lambda expression differ from an anonymous inner class?

Lambda expressions are more concise and focus on the functionality rather than the boilerplate code required by anonymous inner classes. Unlike anonymous inner classes, lambda expressions do not create a separate class file and can only be used with functional interfaces.

24. Can you use this keyword inside a lambda expression?

Yes, the this keyword inside a lambda expression refers to the instance of the enclosing class, not the lambda expression itself. This is different from anonymous inner classes, where this refers to the instance of the inner class.

Java 8 Stream API Coding Questions for Experienced

Here are some common Java 8 Stream API coding questions for experienced candidates, along with their answers:

25. Write a Java 8 program to find the second highest number in a list of integers.

import java.util.Arrays;

import java.util.List;

import java.util.Optional;

public class Main {

    public static void main(String[] args) {

        List<Integer> numbers = Arrays.asList(3, 9, 1, 4, 8, 6);

        Optional<Integer> secondHighest = numbers.stream()

                                                 .sorted((a, b) -> b – a)

                                                 .skip(1)

                                                 .findFirst();

        System.out.println(“Second highest number: ” + secondHighest.orElse(null));

    }

}

26. Write a Java 8 program to remove duplicates from a list of integers.

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {

        List<Integer> numbers = Arrays.asList(1, 2, 3, 3, 4, 5, 5, 6);

        List<Integer> distinctNumbers = numbers.stream()

                                               .distinct()

                                               .collect(Collectors.toList());

        System.out.println(“Distinct numbers: ” + distinctNumbers);

    }

}

27. Write a Java 8 program to partition a list of strings into two lists based on their length (greater than 3 characters).

import java.util.Arrays;

import java.util.List;

import java.util.Map;

import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {

        List<String> strings = Arrays.asList(“Java”, “Go”, “Python”, “C”, “Ruby”);

        Map<Boolean, List<String>> partitioned = strings.stream()

                                                        .collect(Collectors.partitioningBy(s -> s.length() > 3));

        System.out.println(“Strings with length > 3: ” + partitioned.get(true));

        System.out.println(“Strings with length <= 3: ” + partitioned.get(false));

    }

}

28. Write a Java 8 program to convert a list of strings to uppercase.

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {

        List<String> strings = Arrays.asList(“java”, “python”, “c++”, “javascript”);

        List<String> uppercaseStrings = strings.stream()

                                               .map(String::toUpperCase)

                                               .collect(Collectors.toList());

        System.out.println(“Uppercase strings: ” + uppercaseStrings);

    }

}

Scenario-Based Java 8 Interview Questions

Here are some common scenario-based Java 8 interview questions and their answers. 

29. You have a list of strings. How would you filter out the strings that start with the letter ‘A’? 

You can use the filter() method along with a lambda expression to achieve this:

List<String> strings = Arrays.asList(“Apple”, “Banana”, “Apricot”, “Orange”);

List<String> filteredStrings = strings.stream()

                                     .filter(s -> s.startsWith(“A”))

                                     .collect(Collectors.toList());

30. You have a list of integers. How would you find the sum of all even numbers in the list?

You can use the filter() and mapToInt() methods along with the sum() terminal operation to achieve this:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

int sumOfEvenNumbers = numbers.stream()

                              .filter(n -> n % 2 == 0)

                              .mapToInt(Integer::intValue)

                              .sum();

31. You have a collection of employee objects. How would you retrieve the names of all employees? 

You can use the map() method to extract the names of employees:

List<String> employeeNames = employees.stream()

                                     .map(Employee::getName)

                                     .collect(Collectors.toList());

32. You have a list of transactions. How would you find the transaction with the highest amount? 

You can use the max() method to find the transaction with the highest amount:

Transaction maxTransaction = transactions.stream()

                                         .max(Comparator.comparing(Transaction::getAmount))

                                         .orElse(null);

Java 8 Coding Interview Questions

Here are some Java 8 coding practice problems to help you prepare for the interview. 

33. Write a Java 8 program to filter out the even numbers from a list of integers. 

import java.util.Arrays;

import java.util.List;

public class Main {

    public static void main(String[] args) {

        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        numbers.stream()

               .filter(n -> n % 2 == 0)

               .forEach(System.out::println);

    }

}

34. Write a Java 8 program to find the sum of all elements in a list of integers.

import java.util.Arrays;

import java.util.List;

public class Main {

    public static void main(String[] args) {

        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);

        int sum = numbers.stream()

                        .mapToInt(Integer::intValue)

                        .sum();

        System.out.println(“Sum: ” + sum);

    }

}

35. Write a Java 8 program to find the average length of strings in a list of strings. 

This is one of the most common Java 8 interview programs, which you may be asked about during the interview. 

import java.util.Arrays;

import java.util.List;

import java.util.OptionalDouble;

public class Main {

    public static void main(String[] args) {

        List<String> strings = Arrays.asList(“Java”, “Python”, “C++”, “JavaScript”, “Ruby”);

        OptionalDouble averageLength = strings.stream()

                                             .mapToInt(String::length)

                                             .average();

        System.out.println(“Average length of strings: ” + (averageLength.isPresent() ? averageLength.getAsDouble() : 0));

    }

}

Also Read - Top 25+ Interview Questions On String in Java with Answers

36. Write a Java 8 program to check if a given string is a palindrome or not.

This is one of the most common Java 8 coding questions for experienced candidates. 

public class Main {

    public static void main(String[] args) {

        String str = “madam”;

        boolean isPalindrome = IntStream.range(0, str.length() / 2)

                                         .noneMatch(i -> str.charAt(i) != str.charAt(str.length() – i – 1));

        System.out.println(“Is Palindrome: ” + isPalindrome);

    }

}

Note:

Here are some additional Java 8 coding interview questions you should prepare for:

• Write a Java 8 program to sort a list of strings in reverse order.
• Write a Java 8 program to group a list of strings by their length.
• Write a Java 8 program to concatenate a list of strings with a delimiter.
• Write a Java 8 program to count the number of occurrences of each character in a string.
• Write a Java 8 program to find the maximum and minimum values in a list of integers.

Java 8 MCQ Questions

Here are some common MCQ interview questions on Java 8 and their answers. 

37. Which interface represents a function that accepts two arguments and produces a result?

A) Predicate

B) Function

C) BiConsumer

D) Supplier

Answer: C) BiConsumer

38. What is the purpose of the findFirst() method in Java 8 Streams?

A) It finds the first element of the stream.

B) It finds any element of the stream.

C) It filters the elements of the stream based on a predicate.

D) It transforms each element of the stream using a given function.

Answer: A) It finds the first element of the stream.

39. Which of the following represents the correct syntax for creating a Stream in Java 8?

A) List.stream()

B) Arrays.toStream()

C) Stream.of()

D) stream()

Answer: A) List.stream()

40. What is the purpose of the filter() method in Java 8 Streams?

A) It performs an action for each element of the stream.

B) It transforms each element of the stream using a given function.

C) It filters the elements of the stream based on a predicate.

D) It reduces the elements of the stream to a single value.

Answer: C) It filters the elements of the stream based on a predicate.

41. What interface in Java 8 represents a supplier of results?

A) Predicate

B) Function

C) Supplier

D) Consumer

Answer: C) Supplier

42. What is the purpose of the peek() method in Java 8 Streams?

A) It filters the elements of the stream based on a predicate.

B) It performs an action for each element of the stream without changing the elements.

C) It transforms each element of the stream using a given function.

D) It reduces the elements of the stream to a single value.

Answer: B) It performs an action for each element of the stream without changing the elements.

Also Read - Top 20 Array Interview Questions In Java

Wrapping Up

So, these are the top 40+ Java 8 interview questions, along with their answers. Understanding these concepts will greatly improve your preparation for Java 8 interviews. Remember to practice these questions to boost your confidence and readiness. Looking for job opportunities in the IT sector? Check out Hirist, an IT job portal where you can easily find the best job opportunities in the top IT companies.