Simplify First and Last Element Access with JDK 21 Sequenced Collections

In JDK 21, the introduction of Sequenced Collections brings new interfaces and methods to simplify collection handling, addressing the previously non‑uniform and cumbersome ways of accessing the first and last elements of various Java collection types.

Sequenced Collections Interfaces

Sequenced Collections introduced three new interfaces:

SequencedCollection

SequencedMap

SequencedSet

These interfaces provide new methods that improve collection access and manipulation.

Accessing the First and Last Elements

Prior to JDK 21, retrieving the first and last elements required different calls for each collection type:

List: first element – list.get(0); last element – list.get(list.size()-1) Deque: first element – deque.getFirst(); last element – deque.getLast() SortedSet: first element – set.first(); last element – set.last() This disparity made simple operations cumbersome.

In JDK 21, ordered collections such as List, Deque, and Set share unified methods:

First element: collection.getFirst() Last element:

collection.getLast()