Abstract 'class' may be 'interface'
abstract classes that can be converted to interfaces.
Using interfaces instead of classes is preferable as Java doesn't support multiple class inheritance, while a class can implement multiple interfaces.
A class may be converted to an interface if it has no superclasses (other than Object), has only
public static final fields,
public abstract methods, and
public inner classes.
After the quick-fix is applied:
Configure the inspection:
Use the Report classes containing non-abstract methods when using Java 8 option to report only the classes with
static methods and non-abstract methods that can be converted to
default methods (only applicable to language level of 8 or higher).
Report classes containing non-abstract methods when using Java 8
IntelliJ IDEA 2023.3, Qodana for JVM 2023.3