e8879ca088
Co-authored-by: leonardo-pilastri-sonarsource <115481625+leonardo-pilastri-sonarsource@users.noreply.github.com>
49 lines
2.3 KiB
Plaintext
49 lines
2.3 KiB
Plaintext
== Why is this an issue?
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Java 21 introduces the new Sequenced Collections API, which applies to all collections with a defined sequence on their elements, such as `LinkedList`, `TreeSet`, and others (see https://openjdk.org/jeps/431[JEP 431]).
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For projects using Java 21 and onwards, use this API instead of workaround implementations that were necessary before Java 21.
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This rule identifies instances where `Collection.reverse(List)` is used instead of the reversed view of a list (`SequencedCollection.reversed()`).
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It is important to note that this replacement is only valid in cases where the returned list is accessed in a read-only manner.
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This is because `SequencedCollection.reversed()` returns a view of the original list, meaning modifications made to the returned list will be reflected in the original list.
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On the other hand, `Collection.reverse(List)` creates a completely new list that is not connected with the original list.
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`SequencedCollection.reversed()` should be the preferred method for two reasons:
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1. It returns a more lightweight object, as it does not need to recreate the underlying data structure as `Collection.reverse(List)` does. It merely provides a wrapper for element access and the iterator.
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2. It abstracts from the fact that the collection instance is a list. This results in more generic code that is easier to port, for instance, when you want to use another collection data structure.
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== How to fix it
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Replace `Collection.reverse(list)` with `list.reversed()`.
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=== Code examples
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==== Noncompliant code example
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[source,java,diff-id=1,diff-type=noncompliant]
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----
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void foo(List<String> list) {
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var reverseList = Collections.reverse(list); // Noncompliant
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// ... (read-only operations)
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}
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----
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==== Compliant solution
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[source,java,diff-id=1,diff-type=compliant]
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----
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void foo(List<String> list) {
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var reverseList = list.reversed(); // Compliant
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// do something
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// ...
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}
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----
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== Resources
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=== Documentation
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* Java Documentation - https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/SequencedCollection.html[Interface SequencedCollection]
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* OpenJDK - https://openjdk.org/jeps/431[JEP 431: Sequenced Collections]
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* Java Documentation - https://docs.oracle.com/en/java/javase/21/core/creating-sequenced-collections-sets-and-maps.html#GUID-DCFE1D88-A0F5-47DE-A816-AEDA50B97523[Creating Sequenced Collections, Sets, and Maps]
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