Functional Interfaces Flashcards
7 cards from real 1Z0-819 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Functional Interfaces flashcards as text
Which primitive-specialised functional interface avoids boxing when mapping an `int` to an `int`?
Answer: IntUnaryOperator
IntUnaryOperator operates on primitive int values without boxing, whereas the other options involve wrapper types.
What is the difference between `IntFunction` and `ToIntFunction`?
Answer: IntFunction takes an int and returns R; ToIntFunction takes T and returns an int
IntFunction accepts a primitive int and produces a result R; ToIntFunction accepts any T and produces a primitive int.
Which interface does `UnaryOperator` extend?
Answer: Function
UnaryOperator extends Function, specialising it for the case where input and output types are the same.
What does `BinaryOperator.maxBy(Comparator comparator)` return?
Answer: A BinaryOperator that returns the greater of two elements according to the comparator
BinaryOperator.maxBy returns a BinaryOperator that returns the larger of its two operands as determined by the given Comparator.
Which of the following correctly declares a `DoubleSupplier` lambda?
Answer: DoubleSupplier ds = () -> 3;
DoubleSupplier's abstract method getAsDouble() takes no arguments and returns a double; the integer literal 3 is widened automatically.
What is the abstract method of `LongBinaryOperator`?
Answer: applyAsLong(long left, long right)
LongBinaryOperator defines a single abstract method applyAsLong(long left, long right) returning a primitive long.
Which functional interface should you prefer for `x -> x * 2` when `x` is a primitive `int`, to avoid autoboxing?
Answer: IntUnaryOperator
IntUnaryOperator works entirely with primitive int values via applyAsInt(), eliminating all boxing overhead.