Top 10 Java 8 Interview Coding Questions and Answers

Certainly! Here are the top 10 Java 8 interview coding questions and answers:

1. Question: Find the sum of all even numbers in a list using Java 8 streams.

Answer:

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

int sum = numbers.stream()
                .filter(n -> n % 2 == 0)
                .mapToInt(Integer::intValue)
                .sum();
System.out.println("Sum of even numbers: " + sum);

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

int sum = numbers.stream()

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

.mapToInt(Integer::intValue)

.sum();

System.out.println("Sum of even numbers: " + sum);

2. Question: Calculate the square of each number in a list using Java 8 streams.

Answer:

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

List<Integer> squares = numbers.stream()
                               .map(n -> n * n)
                               .collect(Collectors.toList());
System.out.println("Squares: " + squares);

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

List<Integer> squares = numbers.stream()

.map(n -> n * n)

.collect(Collectors.toList());

System.out.println("Squares: " + squares);

3. Question: Remove duplicate elements from a list using Java 8 streams.

Answer:

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

List<Integer> distinctNumbers = numbers.stream()
                                       .distinct()
                                       .collect(Collectors.toList());
System.out.println("Distinct numbers: " + distinctNumbers);

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

List<Integer> distinctNumbers = numbers.stream()

.distinct()

.collect(Collectors.toList());

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

4. Question: Count the number of empty strings in a list of strings using Java 8 streams.

Answer:

List<String> strings = Arrays.asList("Hello", "", "World", "", "Java");

long count = strings.stream()
                    .filter(s -> s.isEmpty())
                    .count();
System.out.println("Number of empty strings: " + count);

List<String> strings = Arrays.asList("Hello", "", "World", "", "Java");

long count = strings.stream()

.filter(s -> s.isEmpty())

.count();

System.out.println("Number of empty strings: " + count);

5. Question: Convert a list of strings to uppercase using Java 8 streams.

Answer:

List<String> strings = Arrays.asList("apple", "banana", "cherry");

List<String> uppercaseStrings = strings.stream()
                                       .map(String::toUpperCase)
                                       .collect(Collectors.toList());
System.out.println("Uppercase strings: " + uppercaseStrings);

List<String> strings = Arrays.asList("apple", "banana", "cherry");

List<String> uppercaseStrings = strings.stream()

.map(String::toUpperCase)

.collect(Collectors.toList());

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

6. Question: Sort a list of strings in descending order using Java 8 streams.

Answer:

List<String> strings = Arrays.asList("apple", "banana", "cherry");

List<String> sortedStrings = strings.stream()
                                   .sorted(Comparator.reverseOrder())
                                   .collect(Collectors.toList());
System.out.println("Sorted strings (descending order): " + sortedStrings);

List<String> strings = Arrays.asList("apple", "banana", "cherry");

List<String> sortedStrings = strings.stream()

.sorted(Comparator.reverseOrder())

.collect(Collectors.toList());

System.out.println("Sorted strings (descending order): " + sortedStrings);

7. Question: Find the maximum value from a list of integers using Java 8 streams.

Answer:

List<Integer> numbers = Arrays.asList(10, 5, 8, 20, 15);

Optional<Integer> max = numbers.stream()
                               .max(Integer::compareTo);
System.out.println("Maximum value: " + max.orElse(0));

List<Integer> numbers = Arrays.asList(10, 5, 8, 20, 15);

Optional<Integer> max = numbers.stream()

.max(Integer::compareTo);

System.out.println("Maximum value: " + max.orElse(0));

8. Question: Check if all elements in a list of strings contain the letter ‘a’ using Java 8 streams.

Answer:

List<String> strings = Arrays.asList("apple", "banana", "cherry");

boolean allContainA = strings.stream()
                            .allMatch(s -> s.contains("a"));
System.out.println("All elements contain 'a': " + allContainA);

List<String> strings = Arrays.asList("apple", "banana", "cherry");

boolean allContainA = strings.stream()

.allMatch(s -> s.contains("a"));

System.out.println("All elements contain 'a': " + allContainA);

9. Question: Group a list of persons by their age using Java 8 streams.

Answer:

List<Person> persons = // List of Person objects with age property

Map<Integer, List<Person>> groupedByAge = persons.stream()
                                                .collect(Collectors.groupingBy(Person::getAge));
System.out.println("Persons grouped by age: " + groupedByAge);

List<Person> persons = // List of Person objects with age property

Map<Integer, List<Person>> groupedByAge = persons.stream()

.collect(Collectors.groupingBy(Person::getAge));

System.out.println("Persons grouped by age: " + groupedByAge);

10. Question: Calculate the average of a list of double values using Java 8 streams.

Answer:

List<Double> values = Arrays.asList(1.5, 2.5, 3.5, 4.5, 5.5);

double average = values.stream()
                       .mapToDouble(Double::doubleValue)
                       .average()
                       .orElse(0.0);
System.out.println("Average: " + average);

List<Double> values = Arrays.asList(1.5, 2.5, 3.5, 4.5, 5.5);

double average = values.stream()

.mapToDouble(Double::doubleValue)

.average()

.orElse(0.0);

System.out.println("Average: " + average);

These questions and answers are intended to test your knowledge of Java 8 features, particularly streams and lambdas. Practice and understand these concepts thoroughly to perform well in Java 8 interviews.