1Z0-819 Functional Interfaces 3

Question 1

Which primitive-specialised functional interface avoids boxing when mapping an `int` to an `int`?

Accepted Answer

IntUnaryOperator

Answer

IntUnaryOperator operates on primitive int values without boxing, whereas the other options involve wrapper types.

Question 2

What is the difference between `IntFunction` and `ToIntFunction`?

Accepted Answer

IntFunction takes an int and returns R; ToIntFunction takes T and returns an int

Answer

IntFunction accepts a primitive int and produces a result R; ToIntFunction accepts any T and produces a primitive int.

Question 3

Which interface does `UnaryOperator<T>` extend?

Accepted Answer

Function<T,T>

Answer

UnaryOperator extends Function, specialising it for the case where input and output types are the same.

Question 4

What does `BinaryOperator.maxBy(Comparator<T> comparator)` return?

Accepted Answer

A BinaryOperator that returns the greater of two elements according to the comparator

Answer

BinaryOperator.maxBy returns a BinaryOperator that returns the larger of its two operands as determined by the given Comparator.

Question 5

Which of the following correctly declares a `DoubleSupplier` lambda?

Accepted Answer

DoubleSupplier ds = () -> 3;

Answer

DoubleSupplier's abstract method getAsDouble() takes no arguments and returns a double; the integer literal 3 is widened automatically.

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