Annotation is not inherited from interface method

Question

I have an interface with an annotated method. The annotation is marked with @Inherited, so I expect an implementor to inherit it. However, it is not the case:

Code:

import java.lang.annotation.Inherited; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.reflect.Method; import java.util.Arrays; public class Example { public static void main(String[] args) throws SecurityException, NoSuchMethodException { TestInterface obj = new TestInterface() { @Override public void m() {} }; printMethodAnnotations(TestInterface.class.getMethod("m")); printMethodAnnotations(obj.getClass().getMethod("m")); } private static void printMethodAnnotations(Method m) { System.out.println(m + ": " + Arrays.toString(m.getAnnotations())); } } interface TestInterface { @TestAnnotation public void m(); } @Retention(RetentionPolicy.RUNTIME) @Inherited @interface TestAnnotation {}

The above code prints:

public abstract void annotations.TestInterface.m(): [@annotations.TestAnnotation()]

public void annotations.Example$1.m(): []

So the question is why does not the obj.m() have @TestAnnotation despite that it implements a method marked with @TestAnnotation which is @Inherited?

The answer was right there in the documentation of @Inherited as pointed out by @AbhinavSakar and @Gilberto. Sorry about that. I did quite a bit of experimentation but missed the obvious - the docs. — vitaly
– vitaly, Commented Sep 14, 2012 at 17:08
By the way, any idea on what is the reason for such a design decision? I would expect the meta-annotation to work on methods too. — vitaly
– vitaly, Commented Sep 14, 2012 at 17:09
No problem, it is surprising that super-classes are treated differently from super-interfaces. That's why some frameworks (such as Spring) ship with reflection utilities that also query the super interfaces. — meriton
– meriton, Commented Sep 14, 2012 at 17:10
org.springframework.core.type.classreading.MetadataReader. — meriton
– meriton, Commented Sep 14, 2012 at 17:25

Abhinav Sarkar · Accepted Answer · 2012-09-14 17:00:28Z

33

From the javadocs of java.lang.annotation.Inherited:

Note that this meta-annotation type has no effect if the annotated type is used to annotate anything other than a class. Note also that this meta-annotation only causes annotations to be inherited from superclasses; annotations on implemented interfaces have no effect.

answered Sep 14, 2012 at 17:00

Abhinav Sarkar

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3 Comments

Gilberto Torrezan Over a year ago

Woa, answered at same time =)

vitaly Over a year ago

I upvoted both, but had to accept only one answer. Sorry, @Gilberto, Abhinav was a tiny bit quicker :)

Gilberto Torrezan Over a year ago

No problem, we are here to help ;-)

Vikdor · Accepted Answer · 2016-05-25 06:09:56Z

From the @Inherited javadoc:

Note that this meta-annotation type has no effect if the annotated type is used to annotate anything other than a class. Note also that this meta-annotation only causes annotations to be inherited from superclasses; annotations on implemented interfaces have no effect.`

In summary, it doesn't apply to methods.

Clijsters · Accepted Answer · 2019-04-30 12:17:05Z

Alternatively, you can use reflection to derive the same information. The method printMethodAnnotations can be rewritten as:

private static void printMethodAnnotations(Method m) { Class<?> methodDeclaredKlass = m.getDeclaringClass(); List<Class<?>> interfases = org.apache.commons.lang3.ClassUtils.getAllInterfaces(methodDeclaredKlass); List<Annotation> annotations = new ArrayList<>(); annotations.addAll(Arrays.asList(m.getAnnotations())); for (Class<?> interfase : interfases) { for (Method interfaseMethod : interfase.getMethods()) { if (areMethodsEqual(interfaseMethod, m)) { annotations.addAll(Arrays.asList(interfaseMethod.getAnnotations())); continue; } } } System.out.println(m + "*: " + annotations); } private static boolean areMethodsEqual(Method m1, Method m2) { // return type, Modifiers are not required to check, if they are not appropriate match then it will be a compile // time error. This needs enhancements for Generic types parameter ? return m1.getName().equals(m2.getName()) && Arrays.equals(m1.getParameterTypes(), m2.getParameterTypes()); }

thanks.. worked for me. But i could find same using spring core's AnnotationUtils. Here is maven dep

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