lundi 10 octobre 2016

Why annotation on generic type argument is not visible for nested type?

I don't get the behaviour of following code: http://ift.tt/2e6Rvn5 - see embedded:

import java.lang.reflect.*;
import java.util.*;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


public class AnnotationOnTypeArgument {

    @Target({ElementType.FIELD,ElementType.PARAMETER,ElementType.METHOD,ElementType.TYPE_USE})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Anno {

    }

    interface Nested<T> {

    }

    Toplevel<@Anno Integer> toplevel;

    Nested<@Anno Integer> nested;

    public static void main(String[] args) throws Exception {
        print(AnnotationOnTypeArgument.class.getDeclaredField("toplevel"));
        print(AnnotationOnTypeArgument.class.getDeclaredField("nested"));
    }

    private static void print(Field field) {
        AnnotatedType annotatedType = field.getAnnotatedType();
        AnnotatedParameterizedType annotatedParameterizedType = (AnnotatedParameterizedType)annotatedType;
        ParameterizedType parameterizedType = (ParameterizedType)annotatedParameterizedType.getType();
        AnnotatedType argType = annotatedParameterizedType.getAnnotatedActualTypeArguments()[0];
        System.out.printf("field %s%ntype=%s%nannotatedType=%s%nannotations=%s%ntype=%s%n%n",
                field.getName(), parameterizedType, argType, Arrays.asList(argType.getDeclaredAnnotations()), argType.getType());
    }

}

interface Toplevel<T> {

}

Why the array of declared annotations on type argument is empty when surrounding type is nested? I expect to have one element just as for top level type. I would appreciate any explanation based on JLS.

Happens consistently on JDK8u101 (http://compilejava.net), older JDK8 and Eclipse.

Thanks!





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