Collection declared by class, not interface

Reports declarations of Collection variables made by using the collection class as a type, rather than an appropriate interface. The warning is not issued if weakening the variable type will cause a compilation error.

Example:

// Warning: concrete collection class ArrayList used.
int getTotalLength(ArrayList<String> list) {
  return list.stream().mapToInt(String::length).sum();
}

// No warning, as trimToSize() method is not
// available in the List interface
void addData(ArrayList<String> data) {
  data.add("Hello");
  data.add("World");
  data.trimToSize();
}

A quick-fix is suggested to use the appropriate collection interface (e.g. Collection, Set, or List).

Inspection options

Option	Type	Default
Ignore local variables	Checkbox	false
Ignore 'private' fields and methods	Checkbox	false

Inspection Details
Available in:	IntelliJ IDEA 2023.3, Qodana for JVM 2023.3
Plugin:	Java, 233.SNAPSHOT

Last modified: 13 July 2023