Core APIs & Data Manipulation Flashcards

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

Answer: getOrDefault()

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

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

Answer: O(n)

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

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

Answer: It returns a canonical String from the string pool

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

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

Answer: Mutations via the wrapper throw UnsupportedOperationException

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

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

Answer: allMatch()

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

What happens when you call `iterator.remove()` without first calling `iterator.next()`?

Answer: Throws IllegalStateException

The `Iterator` contract requires `next()` to be called before `remove()`; violating this throws `IllegalStateException`.

Which `java.time` class represents a date and time WITHOUT a timezone or offset?

Answer: LocalDateTime

`LocalDateTime` holds a date-time with no timezone context; `ZonedDateTime` and `OffsetDateTime` include zone or offset information.