How does Java extend annotation without changing the JVM?

Without JVM changes, how does Java introduce annotation?

Why?

1. Let's first explain why we should introduce it ..

A large number of configuration files will be used in a project. Every small change requires a configuration change. If there is a way for him to change the configuration automatically, how good is it?

At this time, annotation will be introduced.

2. Without JVM changes, how does Java introduce annotation?

(1). encapsulate the interface type into the @ interface type, that is, the annotation type. All of them inherit the annotation interface.

(2) How can Annotation on the method, attribute, and class name be obtained? At this time, reflection and extension of several reflection implementations in JDK are used.

Enable accessibleobject, class, constructor, field, method, and package to implement interface annotatedelement

Then, the annotation information is obtained through reflection.