Java 8 MCQ Questions with Answers

Practice Java 8 MCQs with Detailed Explanations

Answer at least 12 questions to submit and verify answers.

1 Which statement best describes a functional interface in Java 8? Medium

An interface with exactly one abstract method

An interface with no abstract methods

An interface that can only be implemented by lambdas

An interface with default methods only

2 What will be the output of the following code? List<Integer> list = Arrays.asList(1, 2, 3); list.stream().map(x -> x * 2).forEach(System.out::print); Medium

123

246

135

Compilation error

3 Which Stream operation is considered terminal? Medium

map()

filter()

peek()

collect()

4 What is the main purpose of Optional in Java? Medium

To replace all null values automatically

To avoid NullPointerException by explicit absence handling

To improve performance of method calls

To enforce immutability

5 Which default method is added to the Iterable interface in Java 8? Medium

forEach()

stream()

iterator()

spliterator()

6 What will be the output? Stream.of("a", "bb", "ccc") .filter(s -> s.length() > 1) .count(); Medium

Compilation error

7 Which functional interface represents a function that takes an argument and returns no result? Medium

Supplier

Consumer

Predicate

Function

8 Which method is used to create a Stream from a collection? Easy

collection.toStream()

collection.stream()

Stream.of(collection)

collection.asStream()

9 Which Date-Time class in Java 8 is immutable and thread-safe? Medium

Date

Calendar

LocalDate

SimpleDateFormat

10 What happens if a stream has no terminal operation? Medium

It throws an exception

It executes partially

It does not execute at all

It executes eagerly

11 Which method was added to Map in Java 8? Medium

putIfAbsent()

add()

append()

insert()

12 What is the purpose of the @FunctionalInterface annotation? Medium

It enforces exactly one abstract method

It improves runtime performance

It allows multiple inheritance

It enables lambda caching

13 Which method short-circuits a stream? Medium

forEach()

findFirst()

collect()

reduce()

14 What is the return type of Stream.reduce() without an identity value? Medium

Object

Optional<T>

Stream<T>

15 Which Java version introduced the module system? Medium

Java 8

Java 9

Java 10

Java 11

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