Hi, I would like to propose the following new rule:
Unmodifiable collections cannot be modified.
This rule warns about code that attempts to modify an unmodifiable collection.
Keeping the code as it is will result in a java.lang.UnsupportedOperationException.
Noncompliant code examples
List<String> fruits = List.of("apple", "orange");
// ...
int size = fruits.size(); // Compliant
fruits.add("pear"); // Noncompliant; throws runtime exception
fruits.clear(); // Noncompliant; throws runtime exception
Map<String, String> colorsMap = Map.of("sky", "blue", "cloud", "white", "tree", "green");
// ...
colorsMap.putIfAbsent("banana", "yellow"); // Noncompliant; runtime exception here
Compliant code example
List<String> fruits = new ArrayList<>(List.of("apple", "orange"));
fruits.add("pear"); // Compliant; list is modifiable
- external references and/or language specifications:
- https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Collection.html#unmodifiable
- https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Map.html#unmodifiable
- https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Set.html#unmodifiable
- https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/List.html#unmodifiable
The rule should detect all cases where any mutator method is called on an instance that is known to have been created by one of the
java.util.Collections.unmodifiable*, java.util.Collections.empty* or java.util.Collections.singleton* methods or by one of the of(), copyOf(), ofEntries() static factory methods.
- type : Bug