A DESCRIPTION OF THE PROBLEM :
Currently, any project which intends to create a custom subclass of an annotation interface has to reinvent the wheel to correctly implement all the methods specified in `java.lang.annotation.Annotation` and the annotation interface, because the JDK’s implementation is stored in private methods of `sun.reflect.annotation.AnnotationInvocationHandler`.

I propose to add a public API to `java.lang.runtime` for creating `MethodHandle`s and `CallSite`s like `java.lang.runtime.ObjectMethods`, but for `Annotation`s instead of `Record`s.

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Additionally, it would be a quality‑of‑life improvement if compiled annotation interfaces provided default implementations for methods with an `AnnotationDefault` attribute and the `Annotation.annotationType()` method.