Java Annotation Learning Finishing

Java provides four types of meta-annotations that are specifically responsible for the creation of new annotations. Whenever you create a class or interface of a descriptor nature, once it contains repetitive work, you can consider using annotations to simplify and automate the process

@Target

Indicates where the annotation can be used, and the possible ElementType include:

CONSTRUCTOR: Declaration of the constructor

Field: Domain declarations (including enum instances)

local_variable: local variable declaration

Method: Methods Declaration

Package: Packet declaration

PARAMETER: Parameter declaration

Type: class, interface (including annotation type) or enum declaration

@Retention

Indicates the level at which the annotation information needs to be saved, the available retentiontype include

SOURCE: Annotations are discarded by the compiler

Class: Annotations are available in the class file, but are discarded by the VM

RUMTIME:VM will also retain annotations at run time, so the information of annotations can be read through the reflection mechanism

@Documented

Include this note in the Javadoc

@Inherited

Allow subclasses to inherit annotations from parent class

Java Annotation Learning Finishing