Question

I have a parent class Parent and a child class Child, defined thus:

class Parent {
    @MyAnnotation("hello")
    void foo() {
        // implementation irrelevant
    }
}
class Child extends Parent {
    @Override
    foo() {
        // implementation irrelevant
    }
}

If I obtain a Method reference to Child::foo, will childFoo.getAnnotation(MyAnnotation.class) give me @MyAnnotation? Or will it be null?

I’m interested more generally in how or whether annotation works with Java inheritance.

Answer 1

Copied verbatim from http://www.eclipse.org/aspectj/doc/released/adk15notebook/annotations.html#annotation-inheritance:

Annotation Inheritance

It is important to understand the rules relating to inheritance of annotations, as these have a bearing on join point matching based on the presence or absence of annotations.

By default annotations are not inherited. Given the following program

        @MyAnnotation
        class Super {
          @Oneway public void foo() {}
        }

        class Sub extends Super {
          public void foo() {}
        }

Then Sub does not have the MyAnnotation annotation, and Sub.foo() is not an @Oneway method, despite the fact that it overrides Super.foo() which is.

If an annotation type has the meta-annotation @Inherited then an annotation of that type on a class will cause the annotation to be inherited by sub-classes. So, in the example above, if the MyAnnotation type had the @Inherited attribute, then Sub would have the MyAnnotation annotation.

@Inherited annotations are not inherited when used to annotate anything other than a type. A type that implements one or more interfaces never inherits any annotations from the interfaces it implements.