1Z0-819 Core APIs & Data Manipulation 3

Question 1

Which `Map` method returns the value for a key, or a default if the key is absent, WITHOUT inserting the default?

Accepted Answer

getOrDefault()

Answer

`getOrDefault(key, defaultValue)` returns the default when the key is missing but never modifies the map.

Question 2

What is the time complexity of `LinkedList.get(index)` in Java?

Accepted Answer

O(n)

Answer

`LinkedList` is a doubly-linked list; random access by index requires traversal, giving O(n) time.

Question 3

Which statement about `String.intern()` is correct?

Accepted Answer

It returns a canonical String from the string pool

Answer

`intern()` ensures the string is stored in (or retrieved from) the string constant pool, enabling identity equality (`==`) for equal strings.

Question 4

What does `Collections.unmodifiableList(list)` guarantee?

Accepted Answer

Mutations via the wrapper throw UnsupportedOperationException

Answer

The unmodifiable wrapper blocks writes through itself, but the backing list can still be mutated directly; it also provides no thread safety.

Question 5

Which `Stream` terminal operation short-circuits and returns as soon as the predicate fails?

Accepted Answer

allMatch()

Answer

`allMatch()` stops processing as soon as one element does not satisfy the predicate, making it a short-circuit terminal operation.

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