Allow annotations only on classes that inherit or implement parent class

Question

I'm trying to create annotations that are only allowed on certain classes that implement an interface.

Currently, I'm trying to do this to use the Reflections library and loop over all classes with the annotation. This results in a Set<Class<?>>. Since I use generics in the Initializer class, I cannot check if each element in the set is an instance of that type, because instanceOf doesn't work with generics.

public abstract class Initializer<T> {
    private final JavaPlugin plugin;
    private final Set<Class<T>> classSet;

    public Initializer(JavaPlugin plugin, Reflections reflections, Class<? extends Annotation> annotation) {
        this.plugin = plugin;
        // Here I get an error because the required type is Set<Class<T>> and the provided Set<Class<?>>
        this.classSet = reflections.getTypesAnnotatedWith(annotation);
    }

    public JavaPlugin getPlugin() {
        return this.plugin;
    }
}

Can't do this purely with an annotation definition. You could throw an error at run-time with a `Class#isInstance(Object)` or `Class#isAssignableFrom(Class)` check. You could also add compile-time checks with an annotation processor, but you can't enforce the processor is used. — Slaw, Jun 02 '22 at 15:30
I indeed want to have `Set>` but I cannot cast the set returned by the method `getTypesAnnotatedWith()` to this @JohannesKuhn ... — Lennert Soffers, Jun 02 '22 at 15:49
I've tried to use the `Class#isInstance()` but in this case I need to provide an object of T which I don't have in the program — Lennert Soffers, Jun 02 '22 at 15:51
@LennertSoffers Hence why I also suggested `Class#isAssignableFrom(Class)`. — Slaw, Jun 02 '22 at 17:48

Allow annotations only on classes that inherit or implement parent class

0 Answers0