== Why is this an issue?

Java 21 introduces a new SequencedCollection interface that provides a uniform API for accessing its first and last elements.
The new `getFirst()` and `getLast()` methods offer a consistent way to access elements across `SortedSet`, `NavigableSet`, `LinkedHashSet`, `List` and `Deque` collections.
Because those methods are more concise and readable, they should be used instead of more complex workarounds that recreate the same behavior.

For example, `list.get(list.size() - 1)` can be replaced by `list.getLast()`.

This rule identifies code that can be simplified by using the new `getFirst()` and `getLast()` methods.

== How to fix it

Replace the highlighted code with the corresponding `getFirst()` or `getLast()` methods.

=== Code examples

==== Noncompliant code example

[source,java,diff-id=1,diff-type=noncompliant]
----
public String concatenateFirstAndLast(List<String> list) {
  return list.get(0) + // Noncompliant
    list.get(list.size() - 1); // Noncompliant
}
----

==== Compliant solution

[source,java,diff-id=1,diff-type=compliant]
----
public String concatenateFirstAndLast(List<String> list) {
  return list.getFirst() + // Compliant
    list.getLast(); // Compliant
}
----

==== Noncompliant code example

[source,java,diff-id=2,diff-type=noncompliant]
----
public String concatenateFirstAndLast(LinkedHashSet<String> linkedHashSet) {
  return linkedHashSet.iterator().next() + // Noncompliant
    new ArrayList(linkedHashSet).get(linkedHashSet.size() - 1); // Noncompliant
}
----

==== Compliant solution

[source,java,diff-id=2,diff-type=compliant]
----
public String concatenateFirstAndLast(LinkedHashSet<String> linkedHashSet) {
  return linkedHashSet.getFirst() + // Compliant
    linkedHashSet.getLast(); // Compliant
}
----

== Resources

=== Documentation

* https://openjdk.org/jeps/431[JEP 431: Sequenced Collections]
* https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/SequencedCollection.html[Java SE 21 API documentation - SequencedCollection]