Subtle Changes in Java 8: Repeatable Annotations

Apart from the “big stuff”, related to extension methods, lambda, and the streams API, Java 8 also has a couple of minor, very subtle changes. One of them is the fact that you can now annotate an object several times with the same annotation! An example taken from the tutorial:


@Alert(role="Manager")
@Alert(role="Administrator")
public class UnauthorizedAccessException { ... }

For this to work, your @Alert annotation has to be meta-annotated with java.lang.annotation.Repeatable. Tools, which heavily rely on annotation processing may need to review their code to get ready for Java 8. Existing methods, such as AnnotatedElement.getAnnotations(), have not been retrofitted to return repeatable annotations. Instead, other, new methods, such as AnnotatedElement.getAnnotationsByType(Class) and AnnotatedElement.getDeclaredAnnotationsByType(Class) have been added to the JDK, in order to be able to discover repeated annotations on any element. More authoritative information can be found here:

Subtle Changes in Java 8: Repeatable Annotations

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Published by lukaseder

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