Recipe to transform uses of Collections.unmodifiableXX to Immutable Static Factory Methods

[yeikel]

I believe that this belongs here (otherwise please let me know under what module this should be reported)

it would be nice to add a rule to the Java 8 -> Java 11 migration to apply the following transformation :

Before :

Set<String> s = Collections.unmodifiableSet(new HashSet<>(Arrays.asList("A", "B")));

After

Set<String> s = Set.of("A", "B")

Additional resources :

See : https://docs.oracle.com/en/java/javase/11/core/creating-immutable-lists-sets-and-maps.html#GUID-930A5334-9413-4E87-A1D7-6FF4E9E421B2

[yeikel]

Another similar transformation :

final List<String> elements = Collections.unmodifiableList(Arrays.asList("A","B"));
final List<String> elements = List.of("A","B"));

[yeikel]

Another example :

Map<String,String> elements = new HashMap<>();
elements.put("hello","world");
Map<String, String> s = Collections.unmodifiableMap(elements);

Map<String, String> s = Map.of("hello", "world");

[tkvangorder]

@yeikel This is a very good suggestion.

[traceyyoshima]

@yeikel I added the base recipes for the examples you provided in this commit.

I decided not to handle situations like:

Before

List<String> stringList = Arrays.asList("a", "b", "c");
stringList = Collections.unmodifiableList(stringList);

After

List<String> stringList = List.of("a", "b", "c");

Because it would require removing a statement and there could be relevant code in between lines 1 and 2, a multi-variable declaration, etc.

Dataflow analysis is in development and we'll be able to handle the transformation safely once it's finished.

Thanks again for the suggestion!

[yeikel]

@yeikel I added the base recipes for the examples you provided in this commit.

I decided not to handle situations like:

Before

List<String> stringList = Arrays.asList("a", "b", "c");
stringList = Collections.unmodifiableList(stringList);

After

List<String> stringList = List.of("a", "b", "c");

Because it would require removing a statement and there could be relevant code in between lines 1 and 2, a multi-variable declaration, etc.

Dataflow analysis is in development and we'll be able to handle the transformation safely once it's finished.

Thanks again for the suggestion!

Thar makes sense. Thank you for explaining!