Lambda Expressions Flashcards

Which functional interface should you use when a lambda takes two arguments of the same type and returns a result of the same type?

Answer: BinaryOperator

BinaryOperator extends BiFunction and is the correct specialization when both inputs and output share the same type.

What is the result of compiling and running: Predicate p = String::isEmpty; System.out.println(p.test(""));

Answer: true

String::isEmpty is a valid method reference to an instance method, and calling test("") invokes isEmpty() on the empty string, returning true.

Which statement about a lambda expression and its enclosing scope is TRUE?

Answer: Local variables captured by a lambda must be effectively final.

Lambdas can only capture local variables that are final or effectively final; instance and static variables are freely accessible.

Given: Function f = x -> x * 2; Function g = x -> x + 3; what does f.andThen(g).apply(5) return?

Answer: 13

andThen applies f first (5*2=10) then g (10+3=13).

Which of the following is NOT a valid lambda expression in Java 11?

Answer: (int x, y) -> x + y

When parameter types are explicitly listed you must provide types for all parameters; mixing typed and untyped parameters is a compile error.

What does Predicate.not(Predicate) introduced in Java 11 do?

Answer: Negates a predicate returning a new Predicate

Predicate.not(p) is a static factory that returns a new Predicate which is the logical negation of the given predicate.

Which functional interface represents a supplier that may throw a checked exception when used in a custom functional interface?

Answer: Callable

Callable declares throws Exception on its call() method, while Supplier's get() does not declare a checked exception.