Question

I’m trying to find all fields annotated with a custom annotation, but it doesn’t seem to detect it. The same code works fine for standard annotations, such as @Deprecated.

Minimal code to reproduce:

public class MyClass {

    public @interface MyAnnotation {}

    @MyAnnotation Object someObject;
    @MyAnnotation @Deprecated Object someDeprecatedObject;
    @Deprecated Object aThirdObject;

    public static void main(String[] args) {
        Class<?> cls = MyClass.class;

        for (Field field : cls.getDeclaredFields()) {
            System.out.print(field.getName());

            for (Annotation a : field.getDeclaredAnnotations())
                System.out.print(" " + a);

            System.out.println();
        }
    }
}

Output:

someObject
someDeprecatedObject @java.lang.Deprecated()
aThirdObject @java.lang.Deprecated()

@Deprecated comes up, but @MyAnnotation doesn’t! Help!

Answer 1

By default, annotations are not kept at runtime and so cannot be reflected upon. You need to declare your annotation like this to ensure it exists at runtime:

@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
}