1Z0-819 Lambda Expressions 2

Question 1

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

Accepted Answer

BinaryOperator<T>

Answer

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

Question 2

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

Accepted Answer

true

Answer

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

Question 3

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

Accepted Answer

Local variables captured by a lambda must be effectively final.

Answer

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

Question 4

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

Accepted Answer

13

Answer

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

Question 5

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

Accepted Answer

(int x, y) -> x + y

Answer

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

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