OCP Streams and Lambda Expressions 3

Question 1

Which stream operation is guaranteed to be stateful and may require processing the entire stream before producing output?

Accepted Answer

sorted()

Answer

sorted() is a stateful intermediate operation because it must examine all elements to determine their order before emitting any results.

Question 2

What is the difference between findFirst() and findAny() on a sequential stream?

Accepted Answer

On sequential streams they behave identically, always returning the first element

Answer

On sequential streams both findFirst() and findAny() return the first element encountered; the distinction matters only for parallel streams where findAny() may return any element for performance.

Question 3

What happens when you call a terminal operation on a stream that has already been consumed?

Accepted Answer

IllegalStateException is thrown at runtime

Answer

Streams cannot be reused; calling a second terminal operation on an already-consumed stream throws IllegalStateException.

Question 4

Which collector groups stream elements into a Map>?

Accepted Answer

Collectors.partitioningBy(Predicate)

Answer

Collectors.partitioningBy(Predicate) divides stream elements into exactly two groups (true/false) and returns a Map>.

Question 5

What is the return type of Stream.collect(Collectors.toList())?

Accepted Answer

List<T>

Answer

Collectors.toList() accumulates elements into a List; the specification does not guarantee ArrayList, but the return type in the API is List.

(OCP) Oracle Certified Professional Practice Test

(OCP) Oracle Certified Professional Practice Test

OCP Streams and Lambda Expressions 3