Functional Interfaces Flashcards

Which method reference form is used in `Arrays.sort(names, String::compareToIgnoreCase)`?

Answer: Instance method reference on an arbitrary instance of a type

String::compareToIgnoreCase is an instance method reference on an arbitrary instance — the first argument becomes the receiver of the method call.

What functional interface does a constructor reference like `ArrayList::new` satisfy?

Answer: Supplier

ArrayList::new with no arguments matches Supplier because it takes no input and produces a new ArrayList instance.

Given `Function f = Integer::parseInt;`, what kind of method reference is this?

Answer: Static method reference

Integer.parseInt is a static method, so Integer::parseInt is a static method reference.

What does `Comparator.comparing(Person::getName)` return?

Answer: A Comparator that orders persons by their name

Comparator.comparing accepts a key extractor Function and returns a Comparator that orders by the extracted key's natural order.

Which code correctly creates a Comparator that sorts strings by length, then alphabetically?

Answer: Comparator.comparing(String::length).thenComparing(Comparator.naturalOrder())

thenComparing chains a secondary Comparator used only when the primary comparison yields equal results.

What does `Comparator.reversed()` do when chained with `Comparator.comparing(Person::getAge)`?

Answer: Sorts by age in descending order

reversed() returns a Comparator that imposes the reverse ordering of the original, yielding descending age sort.

An interface has one abstract method and one default method. Can it be annotated with `@FunctionalInterface`?

Answer: Yes — default methods do not count toward the single abstract method requirement

@FunctionalInterface requires exactly one abstract method; default and static methods do not affect this count.