Java Collections Framework Flashcards
6 cards from real SCJP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Java Collections Framework flashcards as text
What does the `PriorityQueue` class use to determine the order of elements?
Answer: Natural ordering or a Comparator
`PriorityQueue` orders elements by their natural ordering (Comparable) or by a provided Comparator.
Which interface should be implemented to allow objects to be sorted using `Arrays.sort()` without a Comparator?
Answer: Comparable
Implementing `Comparable` and its `compareTo()` method defines the natural ordering used by `Arrays.sort()` and `Collections.sort()`.
What is the key difference between `HashSet` and `LinkedHashSet`?
Answer: LinkedHashSet maintains insertion order; HashSet does not
`LinkedHashSet` maintains the insertion order of elements using a linked list, while `HashSet` provides no ordering guarantee.
Which method removes all elements from a List in Java?
Answer: clear()
The `clear()` method removes all elements from a collection, leaving it empty.
What exception is thrown when you try to modify a collection while iterating over it with a for-each loop?
Answer: ConcurrentModificationException
Modifying a collection's structure during iteration triggers `ConcurrentModificationException` via the fail-fast iterator mechanism.
Which of the following is the correct way to create an unmodifiable view of a List in Java?
Answer: Collections.unmodifiableList(myList)
`Collections.unmodifiableList()` wraps a List so that any mutating operations throw `UnsupportedOperationException`.
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