OCP Streams and Lambda Expressions 2

Question 1

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

Accepted Answer

average()

Answer

DoubleStream.average() is a terminal operation that returns OptionalDouble containing the arithmetic mean of all elements.

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

flatMap() maps each element to a stream and then flattens all those streams into a single stream, whereas map() returns one element per input element.

Question 3

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

Accepted Answer

Predicate<T>

Answer

Stream.filter() accepts a Predicate<T>, which is a functional interface with a single abstract method test(T t) returning boolean.

Question 4

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

Accepted Answer

6

Answer

reduce(identity, accumulator) returns the result directly (not wrapped in Optional) because the identity element guarantees a value; 0+1+2+3=6.

Question 5

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

Accepted Answer

Stream.generate(Math::random)

Answer

Stream.generate(Supplier<T>) produces an infinite sequential unordered stream where each element is generated by the provided Supplier.

(OCP) Oracle Certified Professional Practice Test

(OCP) Oracle Certified Professional Practice Test

OCP Streams and Lambda Expressions 2