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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

Here you can find the description of settings available for the Collection declared by class, not interface inspection, and the reference of their default values.

Ignore local variables

Not selected

Ignore 'private' fields and methods

Not selected

Inspection Details

By default bundled with:

IntelliJ IDEA 2024.1, Qodana for JVM 2024.1,

Can be installed with plugin:

Java, 241.16690

Last modified: 29 April 2024