1Z0-819 Functional Interfaces 2

Question 1

What is the correct return type of `BiFunction<String, Integer, Boolean>`?

Accepted Answer

Boolean

Answer

The third type parameter of BiFunction<T,U,R> is the return type R, so Boolean is returned.

Question 2

Given `Function f = String::length;` and `Function g = i -> "len:"+i;`, what does `f.andThen(g).apply("hi")` return?

Accepted Answer

"len:2"

Answer

andThen applies f first (length=2) then g, producing "len:2".

Question 3

What is the difference between `Function.andThen(g)` and `Function.compose(g)`?

Accepted Answer

andThen applies g after this function; compose applies g before

Answer

andThen(g) means this → g; compose(g) means g → this, reversing the application order.

Question 4

Which method on `Predicate<T>` returns a new Predicate that is the logical negation of the original?

Accepted Answer

negate()

Answer

Predicate.negate() returns a new Predicate that represents the logical NOT of the original predicate.

Question 5

What does `Predicate.and(Predicate other)` short-circuit on?

Accepted Answer

It short-circuits when the first predicate is false

Answer

Predicate.and() short-circuits on false — if the first predicate returns false, the second is never evaluated.

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