Java Programming — Lambda Expressions Questions & Answers

Q.61 Easy Lambda Expressions

What will be the output of: List list = Arrays.asList("a", "bb", "ccc"); list.forEach(s -> System.out.print(s.length() + " "));

A 1 2 3

B a bb ccc

C 3 2 1

D 1 1 1

Correct Answer: A. 1 2 3

EXPLANATION

The lambda expression prints the length of each string. Lengths are 1, 2, and 3 respectively, with spaces between them.

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Q.62 Easy Lambda Expressions

What is the primary advantage of using lambda expressions in Java 8+?

A They reduce boilerplate code and enable functional programming style

B They increase execution speed significantly

C They eliminate the need for classes

D They are required for all stream operations

Correct Answer: A. They reduce boilerplate code and enable functional programming style

EXPLANATION

Lambda expressions reduce boilerplate code by allowing inline implementation of functional interfaces without creating anonymous inner classes, enabling a more functional programming style.

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Q.63 Hard Lambda Expressions

Consider: Function curry = x -> y -> x + y; What does curry.apply(5).apply(3) return?

A 8

B 15

C 5

D 3

Correct Answer: A. 8

EXPLANATION

This is a curried function. curry.apply(5) returns a function that adds 5. Applying that with 3 gives 5 + 3 = 8.

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Q.64 Hard Lambda Expressions

What issue can arise when using lambda expressions with flatMap() in nested streams?

A Excessive memory consumption from creating multiple intermediate streams

B flatMap() cannot accept lambda expressions

C Type erasure causes ClassCastException

D Lambda expressions become unreadable

Correct Answer: A. Excessive memory consumption from creating multiple intermediate streams

EXPLANATION

Each flatMap creates intermediate streams. Deeply nested flatMap with lambdas can consume significant memory, especially with large datasets.

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Q.65 Hard Lambda Expressions

Consider: List list = Arrays.asList("a", "b", "c"); list.stream().collect(Collectors.toMap(s -> s, s -> s.length())). What type is returned?

A Map

B Map

C List

D Set

Correct Answer: A. Map

EXPLANATION

Collectors.toMap with key mapper (s -> s) produces String keys and value mapper (s -> s.length()) produces Integer values, resulting in Map<String, Integer>.

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Q.66 Hard Lambda Expressions

What is the time complexity of reducing a stream with a lambda expression using reduce()?

A O(n) in sequential, potentially O(log n) in parallel with proper associative operation

B Always O(1)

C O(n²) regardless of parallelism

D O(n log n) always

Correct Answer: A. O(n) in sequential, potentially O(log n) in parallel with proper associative operation

EXPLANATION

Sequential reduce is O(n). Parallel reduction can be O(log n) with a properly associative and commutative operation, enabling divide-and-conquer approach.

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Q.67 Hard Lambda Expressions

Consider a lambda that needs to throw a checked exception. Which approach is correct?

A Wrap the checked exception in a try-catch block within the lambda

B Create a custom functional interface with throws clause

C Use @FunctionalInterface with throws declaration

D Lambda expressions cannot throw checked exceptions

Correct Answer: A. Wrap the checked exception in a try-catch block within the lambda

EXPLANATION

Lambda expressions don't propagate checked exceptions. They must be caught within the lambda body using try-catch.

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Q.68 Medium Lambda Expressions

What will be the output of: IntStream.range(1, 4).map(x -> x * 2).sum();

A 12

B 9

C 6

D 24

Correct Answer: A. 12

EXPLANATION

range(1, 4) generates [1, 2, 3]. After map(x -> x * 2): [2, 4, 6]. Sum = 2 + 4 + 6 = 12.

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Q.69 Medium Lambda Expressions

In the lambda expression (a, b) -> a.compareTo(b), what is the implicit functional interface?

A Comparator

B BiFunction

C BiPredicate

D BinaryOperator

Correct Answer: A. Comparator

EXPLANATION

The Comparator<T> functional interface has the method compare(T a, T b) which returns an int, matching this lambda's behavior.

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Q.70 Medium Lambda Expressions

What is the difference between peek() and forEach() when used with lambda expressions in Streams?

A peek() is intermediate and doesn't consume the stream, forEach() is terminal and consumes it

B forEach() is faster than peek()

C peek() can only be used with Collectors

D forEach() returns a value while peek() returns void

Correct Answer: A. peek() is intermediate and doesn't consume the stream, forEach() is terminal and consumes it

EXPLANATION

peek() is an intermediate operation used for debugging; it doesn't end the stream. forEach() is a terminal operation that consumes the stream.

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