Use cases for implementing annotations

Question

What are valid use cases for implementing annotations?

When designing primarily annotation based configuration systems I occasionally need to create classes which i

Answer 1

JAXBIntroductions is a good example: it allows configuring JAXB annotations using XML files. Two main use cases come to mind: configuring classes you don't have source access or different configurations for one class.

In general, I think instantiating annotations dynamically to pass them to frameworks is generally a good use case. However, if you are the designer of this framework, I certainly would think twice though.