OCP Streams and Lambda Expressions 2

Question 1

Which terminal operation returns an OptionalDouble representing the average of a DoubleStream?

Accepted Answer

average()

Answer

mean()

Answer

sum()

Answer

reduce()

Question 2

What does the flatMap() operation do that map() does not?

Accepted Answer

It flattens a stream of streams into a single stream

Answer

It applies a function to each element and returns a new stream of the same size

Answer

It filters elements based on a predicate

Answer

It sorts elements in natural order

Question 3

Which functional interface is used by Stream.filter()?

Accepted Answer

Predicate<T>

Answer

Function<T,R>

Answer

Consumer<T>

Answer

Supplier<T>

Question 4

What is the result of calling Stream.of(1, 2, 3).reduce(0, Integer::sum)?

Accepted Answer

6

Answer

Optional[6]

Answer

0

Answer

Compilation error

Question 5

Which of the following creates a lazy infinite stream of random doubles?

Accepted Answer

Stream.generate(Math::random)

Answer

Stream.of(Math::random)

Answer

Stream.iterate(0.0, Math::random)

Answer

DoubleStream.builder().build()

Question 6

What does Collectors.joining(", ") do when used with Stream.collect()?

Accepted Answer

Concatenates stream elements into a single String separated by ", "

Answer

Groups elements into a Map by a delimiter

Answer

Joins two streams together

Answer

Collects elements into a List joined as comma-separated values

Question 7

Which method on Optional executes an action only if a value is present?

Accepted Answer

ifPresent(Consumer)

Answer

orElse(T)

Answer

filter(Predicate)

Answer

map(Function)