Java SequencedCollection for Ordered Data Structures: SequencedList, SequencedSet, and SequencedDeque

Learn how Java 21’s SequencedCollection simplifies working with ordered data structures. See how it enhances List, Deque, and Set with examples.

🚀 Introduction: Why SequencedCollection in Java 21?

Before Java 21, working with ordered data structures required different methods for accessing the first and last elements.

For example:

• List → list.get(0), list.get(list.size() - 1)
• Deque → deque.getFirst(), deque.getLast()
• Set (e.g., LinkedHashSet) → No direct way to get the first/last element

💡 Java 21 introduces SequencedCollection, a new interface that provides consistent methods for handling ordered data structures.

📌 In this article, you’ll learn:
✅ What SequencedCollection is and why it matters
✅ How it improves List, Set, and Deque
✅ Complete examples demonstrating each SequencedCollection type

🔍 What is SequencedCollection in Java 21?

SequencedCollection is a new interface in Java 21 that provides a unified way to manage ordered data in collections.