Menu
java.lang.annotation.ElementType:
A program element type. The constants of this enumerated type provide a simple classification of the declared elements in a Java program. These constants are used with the Target meta-annotation type to specify where it is legal to use an annotation type.
There are the following constants:
Can someone explain what each of them are (where they'd be annotated in actual code)?
637
@Target(ElementType. ANNOTATION_TYPE) it is a tool that allows to extend the use of annotations. Follow this answer to receive notifications.
This @Target meta-annotation indicates that the declared type is intended solely for use as a member type in complex annotation type declarations. It cannot be used to annotate anything directly: @Target({}) public @interface MemberType { ... }
@interface is used to create your own (custom) Java annotations. Annotations are defined in their own file, just like a Java class or interface. Here is custom Java annotation example: @interface MyAnnotation { String value(); String name(); int age(); String[] newNames(); }
java.lang.annotation.Target. Indicates the contexts in which an annotation type is applicable. The declaration contexts and type contexts in which an annotation type may be applicable are specified in JLS 9.6. 4.1, and denoted in source code by enum constants of java.
Let's say the annotation to which you specify the ElementType is called YourAnnotation:
ANNOTATION_TYPE - Annotation type declaration. Note: This goes on other annotations
@YourAnnotation public @interface AnotherAnnotation {..} CONSTRUCTOR - Constructor declaration
public class SomeClass { @YourAnnotation public SomeClass() {..} } FIELD - Field declaration (includes enum constants)
@YourAnnotation private String someField; LOCAL_VARIABLE - Local variable declaration. Note: This can't be read at runtime, so it is used only for compile-time things, like the @SuppressWarnings annotation.
public void someMethod() { @YourAnnotation int a = 0; } METHOD - Method declaration
@YourAnnotation public void someMethod() {..} PACKAGE - Package declaration. Note: This can be used only in package-info.java.
@YourAnnotation package org.yourcompany.somepackage; PARAMETER - Parameter declaration
public void someMethod(@YourAnnotation param) {..} TYPE - Class, interface (including annotation type), or enum declaration
@YourAnnotation public class SomeClass {..} You can specify multiple ElementTypes for a given annotation. E.g.:
@Target({ElementType.CONSTRUCTOR, ElementType.METHOD}) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
