Core Java API Flashcards

Which method in `Iterable` is used to perform an action for each element?

Answer: forEach()

`Iterable.forEach(Consumer)` iterates over all elements and applies the given action to each.

What is the result of `new StringBuilder("abc").insert(1, "XY")`?

Answer: "aXYbc"

`insert(1, "XY")` inserts "XY" starting at index 1, shifting existing characters right, resulting in "aXYbc".

Which of these correctly declares a `Set` that preserves insertion order?

Answer: new LinkedHashSet<>()

`LinkedHashSet` maintains insertion order using a doubly-linked list alongside the hash table.

What does `LocalDate.now().plusMonths(1).getMonth()` return if today is January 31?

Answer: February

Adding one month to January 31 yields February 28 (or 29 in a leap year); the month is February.

What is the output of `System.out.println(" hello ".strip())`?

Answer: "hello"

`String.strip()` removes leading and trailing whitespace (including Unicode whitespace), returning "hello".

Which collection class is thread-safe and allows concurrent reads and writes?

Answer: ConcurrentHashMap

`ConcurrentHashMap` uses segmented locking to allow concurrent reads and a limited number of concurrent writes safely.

What is the return type of `Map.entrySet()`?

Answer: Set>

`Map.entrySet()` returns a `Set>` containing all key-value pair entries in the map.