Class DesignForExtensionCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable

    public class DesignForExtensionCheck
    extends AbstractCheck
    The check finds classes that are designed for extension (subclass creation).

    Nothing wrong could be with founded classes. This check makes sense only for library projects (not an application projects) which care of ideal OOP-design to make sure that class works in all cases even misusage. Even in library projects this check most likely will find classes that are designed for extension by somebody. User needs to use suppressions extensively to got a benefit from this check, and keep in suppressions all confirmed/known classes that are deigned for inheritance intentionally to let the check catch only new classes, and bring this to team/user attention.

    ATTENTION: Only user can decide whether a class is designed for extension or not. The check just shows all classes which are possibly designed for extension. If smth inappropriate is found please use suppression.

    ATTENTION: If the method which can be overridden in a subclass has a javadoc comment (a good practise is to explain its self-use of overridable methods) the check will not rise a violation. The violation can also be skipped if the method which can be overridden in a subclass has one or more annotations that are specified in ignoredAnnotations option. Note, that by default @Override annotation is not included in the ignoredAnnotations set as in a subclass the method which has the annotation can also be overridden in its subclass.

    More specifically, the check enforces a programming style where superclasses provide empty "hooks" that can be implemented by subclasses.

    The check finds classes that have overridable methods (public or protected methods that are non-static, not-final, non-abstract) and have non-empty implementation.

    This protects superclasses against being broken by subclasses. The downside is that subclasses are limited in their flexibility, in particular, they cannot prevent execution of code in the superclass, but that also means that subclasses cannot forget to call their super method.

    The check has the following options:

    • ignoredAnnotations - annotations which allow the check to skip the method from validation. Default value is Test, Before, After, BeforeClass, AfterClass.
    Author:
    lkuehne, Andrei Selkin