[Java] Annotation

Annotation definition

-If @interface is added, it will be defined as an annotation.

Annotation parameter definition

--Declaration of parameters when using annotations


public @interface TestAnnotation {
    String param1();
    String param2() default "defaultValue";


@TestAnnotation (param1="30", param2="100")
public UserAnnotation() {}

Annotation reference

--Refer to using reflection.

Reference class

    Class<?> c = UserAnnotation.class;
    for (Annotation a : c.getDeclaredAnnotations()) {

Console output

@com.example.demo.com.annotation.TestAnnotation(param2=100, param1=30)

Meta annotation


@Target({ElementType.TYPE, ElementType.ANNOTATION_TYPE})
public @interface TestAnnotation{}

--Annotation attached to an annotation. --Of these, the one prepared on the java side is called the standard meta annotation.
ex. Documented, Target, Retention, Ingerited

@Documented --Whether to include annotation description in Javadoc.

@Target --Define where to place annotations.

type Description
TYPE Class interface, enum, annotation
FIELD field
ANNOTATION_TYPE Annotation type declaration

@Retantion ――How far will the annotation information be used?

type Description
SOURCE It is retained only on the source and deleted when the class file is created.
CLASS It can be retained in a class file, but it cannot be referenced when the application is executed.
RUNTIME Can be used even when the application is executed.
This is necessary if you want to refer to annotations in reflection.

@Inherited --Add annotation information to the subclass that declares the class.

Reference site

@Documented behavior https://qiita.com/opengl-8080/items/1cc996d9e8bb5c811567

What is @meta-annotation? https://www.techscore.com/tech/Java/JavaSE/JavaLanguage/7-3/

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