1Z0-819 Stream API 5

Question 1

Which terminal operation must be used if you need the result to maintain encounter order in a parallel stream?

Accepted Answer

forEachOrdered()

Answer

forEachOrdered() respects the encounter order even in parallel streams, unlike forEach() which may process elements in any order.

Question 2

What does Collectors.summarizingInt(ToIntFunction) produce?

Accepted Answer

An IntSummaryStatistics object

Answer

summarizingInt() collects count, sum, min, max, and average into an IntSummaryStatistics instance.

Question 3

Which method creates a Stream by reading lines from a file and is defined in java.nio.file.Files?

Accepted Answer

Files.lines()

Answer

Files.lines(Path) returns a lazily-populated Stream<String> of lines from the file.

Question 4

What is the difference between Stream.anyMatch() and Stream.allMatch() when the stream is empty?

Accepted Answer

anyMatch returns false; allMatch returns true

Answer

On an empty stream, anyMatch() returns false (vacuously no element satisfies the predicate) and allMatch() returns true (vacuously all elements satisfy).

Question 5

Which collector can be used to produce a Map> from a stream?

Accepted Answer

Collectors.partitioningBy()

Answer

partitioningBy(Predicate) always produces a two-entry Map> keyed on true and false.

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

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

1Z0-819 Stream API 5