Collections Framework Flashcards

Which method in the `List` interface returns an unmodifiable view of the list in Java 11?

Answer: Collections.unmodifiableList(list)

`Collections.unmodifiableList()` wraps an existing list in an unmodifiable view, while `List.copyOf()` creates a new independent unmodifiable copy.

What happens when you call `Map.entry(key, value)` in Java 11 and then try to call `setValue()` on the returned entry?

Answer: It throws UnsupportedOperationException

`Map.entry()` returns an immutable `Map.Entry`, so calling `setValue()` throws `UnsupportedOperationException`.

Which `NavigableMap` method returns the greatest key strictly less than the given key, or null if there is no such key?

Answer: lowerKey()

`lowerKey(k)` returns the greatest key strictly less than `k`, while `floorKey(k)` returns the greatest key less than or equal to `k`.

Which of the following correctly describes the behavior of `LinkedHashMap` regarding iteration order?

Answer: Iterates in insertion order by default

`LinkedHashMap` maintains a doubly-linked list to preserve insertion order (or access order if constructed with `accessOrder=true`).

What is the return type of `Collections.frequency(Collection c, Object o)`?

Answer: int

`Collections.frequency()` returns a primitive `int` representing the number of times the specified element appears in the collection.

Which `Deque` method retrieves but does NOT remove the head of the queue, and returns null if the deque is empty?

Answer: peek()

Both `peek()` and `peekFirst()` return null for an empty deque; `peek()` is the `Queue`-interface method equivalent to `peekFirst()` in `Deque`.

When iterating over a `HashSet` and calling `iterator.remove()`, what is the result?

Answer: Removes the element safely without ConcurrentModificationException

Using the iterator's own `remove()` method is the safe way to remove elements during iteration and does not throw `ConcurrentModificationException`.