Java Collections Framework Flashcards

What happens when you call `TreeMap.subMap(fromKey, toKey)` and then try to insert a key outside that range into the returned view?

Answer: An IllegalArgumentException is thrown

Inserting a key outside the range of a subMap view throws IllegalArgumentException because the view enforces its boundary constraints.

Which statement is true about `LinkedHashMap`?

Answer: It maintains insertion order by default

LinkedHashMap maintains insertion order (or optionally access order) by using a doubly-linked list alongside the hash table.

Given `List list = Arrays.asList("a", "b", "c");`, what happens when you call `list.add("d")`?

Answer: An UnsupportedOperationException is thrown

Arrays.asList() returns a fixed-size list backed by the array; structural modifications like add() throw UnsupportedOperationException.

Which collection class is best suited for implementing a LIFO (Last-In-First-Out) stack in modern Java?

Answer: java.util.ArrayDeque

ArrayDeque is the preferred stack implementation because it is faster than Stack (which is synchronized) and more memory-efficient than LinkedList.

What is the contract between `equals()` and `hashCode()` that must be satisfied for objects used as HashMap keys?

Answer: If a.equals(b) is true, a.hashCode() must equal b.hashCode()

The contract requires that equal objects must have the same hash code; unequal objects may share hash codes (collisions are allowed).

Which interface does `PriorityQueue` implement that defines its ordering behavior?

Answer: Queue

PriorityQueue implements the Queue interface; ordering is determined by the natural order of elements or a Comparator passed at construction.

When iterating over a `HashMap` with an `Iterator` and you remove an element using `map.remove(key)` (not `iterator.remove()`), what occurs?

Answer: A ConcurrentModificationException is thrown on the next iterator call

Structurally modifying a HashMap while iterating it via a fail-fast iterator (without using iterator.remove()) causes ConcurrentModificationException.