1Z0-819 Stream API 2

Question 1

Which terminal operation on a Stream returns an OptionalInt containing the minimum value?

Accepted Answer

IntStream.min()

Answer

IntStream.min() returns an OptionalInt with the minimum value of the stream.

Question 2

What does the following produce? Stream.of(1,2,3).map(n -> n * 2).filter(n -> n > 3).count()

Accepted Answer

2

Answer

After doubling: 2,4,6; filtering >3 yields 4,6; count() returns 2.

Question 3

Which Collector groups elements into a Map where keys are Boolean values?

Accepted Answer

Collectors.partitioningBy()

Answer

Collectors.partitioningBy() splits elements into true/false groups based on a Predicate.

Question 4

What is the result of IntStream.range(0, 5).sum()?

Accepted Answer

10

Answer

IntStream.range(0,5) produces 0,1,2,3,4; their sum is 10.

Question 5

Which method converts a Stream> to a Stream containing only present values in Java 9+?

Accepted Answer

stream.flatMap(Optional::stream)

Answer

Optional.stream() was added in Java 9, making flatMap(Optional::stream) the idiomatic approach.

(1Z0-819) Oracle Java SE 11 Developer Practice Test