Q68: What are Sequenced Collections introduced in Java 21?
Java 21 introduced unified interfaces for collections with defined encounter order: SequencedCollection, SequencedSet, SequencedMap.
- Standardized Methods:
addFirst(),addLast(),getFirst(),getLast(),removeFirst(),removeLast(), andreversed()(returns a reverse-ordered view).
SequencedCollection Operations
List<String> list = new ArrayList<>(List.of("B", "C"));
list.addFirst("A"); // [A, B, C]
list.addLast("D"); // [A, B, C, D]
String first = list.getFirst(); // "A"
List<String> reversed = list.reversed(); // [D, C, B, A]💡 SequencedCollection standardizes first/last access and reverse-view operations.
Key Takeaways
- Unified interfaces for collections with defined element ordering.
- Provides standardized methods:
getFirst(),getLast(),reversed().
Knowledge Check
Which method in SequencedCollection returns a reverse-ordered view of the underlying collection?