Which of the following lambda expressions is INCORRECT?
Answer: C
In option C, you cannot specify types in lambda parameters when using implicit typing. It should be either (x, y) or explicitly define all parameters.
Q.822Medium
Consider: Stream.of(1, 2, 3, 4, 5).filter(x -> x > 2).map(x -> x * x). What will the terminal operation need to be?
Answer: C
Both collect() and forEach() are valid terminal operations. collect() returns a list, forEach() performs an action. reduce() is also valid but would sum the squares.
Q.823Medium
What is method reference (::) in Java and how does it relate to lambda expressions?
Answer: A
Method reference (::) is syntactic sugar for lambda expressions. System.out::println is equivalent to x -> System.out.println(x).
Q.824Medium
What is the difference between peek() and forEach() when used with lambda expressions in Streams?
Answer: A
peek() is an intermediate operation used for debugging; it doesn't end the stream. forEach() is a terminal operation that consumes the stream.
Q.825Medium
In the lambda expression (a, b) -> a.compareTo(b), what is the implicit functional interface?
Answer: A
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.826Medium
What will be the output of: IntStream.range(1, 4).map(x -> x * 2).sum();
Answer: A
range(1, 4) generates [1, 2, 3]. After map(x -> x * 2): [2, 4, 6]. Sum = 2 + 4 + 6 = 12.
Q.827Hard
Consider a lambda that needs to throw a checked exception. Which approach is correct?
Answer: A
Lambda expressions don't propagate checked exceptions. They must be caught within the lambda body using try-catch.
Q.828Hard
What is the time complexity of reducing a stream with a lambda expression using reduce()?
Answer: A
Sequential reduce is O(n). Parallel reduction can be O(log n) with a properly associative and commutative operation, enabling divide-and-conquer approach.
Q.829Hard
Consider: List<String> list = Arrays.asList("a", "b", "c"); list.stream().collect(Collectors.toMap(s -> s, s -> s.length())). What type is returned?
Answer: A
Collectors.toMap with key mapper (s -> s) produces String keys and value mapper (s -> s.length()) produces Integer values, resulting in Map<String, Integer>.
Q.830Hard
What issue can arise when using lambda expressions with flatMap() in nested streams?
Answer: A
Each flatMap creates intermediate streams. Deeply nested flatMap with lambdas can consume significant memory, especially with large datasets.
Q.831Hard
Consider: Function<Integer, Function<Integer, Integer>> curry = x -> y -> x + y; What does curry.apply(5).apply(3) return?
Answer: A
This is a curried function. curry.apply(5) returns a function that adds 5. Applying that with 3 gives 5 + 3 = 8.
Q.832Easy
What is the primary advantage of using lambda expressions in Java 8+?
Answer: A
Lambda expressions reduce boilerplate code by allowing inline implementation of functional interfaces without creating anonymous inner classes, enabling a more functional programming style.
Q.833Easy
What will be the output of: List<String> list = Arrays.asList("a", "bb", "ccc"); list.forEach(s -> System.out.print(s.length() + " "));
Answer: A
The lambda expression prints the length of each string. Lengths are 1, 2, and 3 respectively, with spaces between them.
Q.834Easy
Which functional interface is used for operations that take two arguments and return a single value?
Answer: B
BiFunction<T, U, R> represents a function that accepts two arguments of types T and U, and returns a result of type R.
Q.835Easy
What is a method reference (::) in Java?
Answer: A
Method references are compact lambda expressions that directly reference existing methods. They use :: syntax and are equivalent to lambdas that call those methods.
Q.836Medium
Consider: Stream.of(1, 2, 3, 4, 5).filter(x -> x > 2).map(x -> x * 2).forEach(System.out::println); What will be the output?
Answer: A
filter(x -> x > 2) keeps 3, 4, 5. map(x -> x * 2) transforms them to 6, 8, 10. forEach prints each value.
Q.837Medium
What is the difference between peek() and forEach() in streams?
Answer: B
peek() is an intermediate operation that returns a stream for chaining, useful for debugging. forEach() is terminal and returns void, ending the stream chain.
Q.838Medium
What issue can arise when using lambda expressions with checked exceptions?
Answer: B
Since standard functional interfaces don't declare checked exceptions, you must either wrap in try-catch or create a custom functional interface that throws the checked exception.
Q.839Medium
What will be the output of: IntStream.range(1, 4).map(x -> x * x).forEach(System.out::print);
Answer: A
range(1, 4) generates 1, 2, 3. map(x -> x * x) produces 1, 4, 9. Printed without spaces gives '149'.
Q.840Medium
In the lambda expression (a, b) -> a.compareTo(b), what can we infer about the parameters?
Answer: D
Without explicit type declarations or context, the compiler must infer types from usage. We can only determine they have a compareTo() method, likely Comparable types.
