1Z0-819 Lambda Expressions 3

Question 1

What is the target type of a lambda expression?

Accepted Answer

The functional interface type inferred from context

Answer

The target type is the functional interface that the compiler infers from the assignment, method argument, or cast context where the lambda appears.

Question 2

Given: Consumer c1 = s -> System.out.print(s); Consumer c2 = s -> System.out.print(s.length()); Consumer combined = c1.andThen(c2); combined.accept("Hi"); — what is printed?

Accepted Answer

Hi2

Answer

Consumer.andThen chains consumers in order, so c1 prints "Hi" then c2 prints "2", producing "Hi2".

Question 3

Which of the following correctly uses a constructor reference?

Accepted Answer

Supplier> s = ArrayList::new;

Answer

ArrayList::new is a valid constructor reference that matches the Supplier> functional interface because ArrayList has a no-arg constructor.

Question 4

In Java 11, which method of Function<T,R> allows composing a function BEFORE the current one?

Accepted Answer

compose

Answer

Function.compose(before) returns a composed function that applies 'before' first and then applies the current function to the result.

Question 5

What happens if you assign the same lambda body to two different compatible functional interface variables?

Accepted Answer

It works; the lambda adopts each interface's target type independently

Answer

A lambda expression is poly-expression and can be assigned to any compatible functional interface; each assignment creates an independent instance.

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

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

1Z0-819 Lambda Expressions 3