CODEWITHSUNDEEP
javaannotations
vitaly
vitaly

Reputation: 2945

Annotation is not inherited from interface method

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?

Upvotes: 14

Views: 13309

Answers (3)

Sridivakar
Sridivakar

Reputation: 163

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());
}

Upvotes: 3

Gilberto Torrezan
Gilberto Torrezan

Reputation: 5277

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.

Upvotes: 23

Abhinav Sarkar
Abhinav Sarkar

Reputation: 23812

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.

Upvotes: 33

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