{"id":1676,"date":"2011-03-16T11:08:27","date_gmt":"2011-03-16T05:38:27","guid":{"rendered":"http:\/\/JitendraZaa.com\/blog\/?p=1676"},"modified":"2011-03-16T11:08:27","modified_gmt":"2011-03-16T05:38:27","slug":"meta-annotation-annotate-other-annotation","status":"publish","type":"post","link":"https:\/\/www.jitendrazaa.com\/blog\/java\/meta-annotation-annotate-other-annotation\/","title":{"rendered":"Meta Annotation – annotate other annotation"},"content":{"rendered":"

In Previous article, we have seen that what are the types of annotation provided by the JAVA.<\/a><\/p>\n

What is Meta Annotation ?<\/strong><\/p>\n

Fortunately Java allows us to define our own annotation. The annotations which are used to define\u00a0costume\u00a0annotations are known as “Meta Annotation<\/strong>“.<\/p>\n

There are four annotation types in the “java.lang.annotation”<\/em> package. These so-called meta-annotations are used to annotate other annotation types.<\/p>\n

\n
\n
\"Inbuilt<\/a><\/dt>\n
Inbuilt Annotation and Meta Annotations in JAVA<\/dd>\n<\/dl>\n<\/div>\n


\n1. @Documented:<\/strong>
\nIf the Annotation itself is annotated by @Documented, then in the java documentation, annotation will also be shown with the description of class and members.<\/strong><\/p>\n

For Example:<\/p>\n

\npackage com.G2.Annotations.Meta;\n\nimport java.lang.annotation.Documented;\n\n@Documented\n@interface Nagpur{}\n\n@interface Mumbai{}\n\n@Mumbai\n@Nagpur\npublic class TestDocumented {\n\n}\n\n<\/pre>\n
In above code, when the documentation for the class “TestDocumented”\u009d is generated, @Nagpur will be shown in the document whereas Mumbai will not.<\/p>\n
2.   @ Inherited:<\/strong>
\nIf any Annotation is marked by @Inherited then the child class inherits that annotation.<\/strong>
\nExample :<\/p>\n
\npackage com.G2.Annotations.Meta;\n\nimport java.lang.annotation.Inherited;\n\n@Inherited\n@interface Maharashtra {\n}\n\n@interface Gujarat {\n}\n\n@Maharashtra\n@Gujarat\nclass Gujrat_Maharashtra {\n\n}\n\nclass Nag extends Gujrat_Maharashtra {\n\tpublic void display() {\n\t\tSystem.out.println("Nagpur is in Maharashtra");\n\t}\n}\n\n<\/pre>\n
In above example, there are two annotations defined:  “@Maharashtra”\u009d and “@Gujrat”\u009d.
\nSubclass “Nag”\u009d inherited annotation “@Maharashtra”\u009d only from its parent class “Gujarat_Maharashtra”\u009d, because it is marked as @Inherited.<\/p>\n
3.\t@Retention<\/strong>
\nDifferent annotation types have different purposes. Some are intended for use with the compiler; others are meant to be reflected dynamically at runtime. There’s no reason for a compiler annotation to be available at runtime.<\/strong>
\nThis Meta annotation \u2013 @Retention is responsible to specify that how long an annotation type should be retained.<\/strong><\/em><\/p>\n
The value attribute is one of the “java.lang.annotation.Retention”<\/em> Policy enum constants. The possible values, in order from shortest to longest retention, are as follows:<\/p>\n
RetentionPolicy.SOURCE<\/strong>
\nThe annotation will not be included in the class file. This is useful for annotations which are intended for the compiler only.<\/p>\n
RetentionPolicy.CLASS<\/strong>
\nThe annotation will be included in the class file, but cannot be read reflectively.<\/p>\n
RetentionPolicy.RUNTIME<\/strong>
\nThe annotation can be reflected at runtime.<\/p>\n
If no @Retention policy is specified, it defaults to RetentionPolicy.CLASS.<\/em><\/p>\n
4.\t@Target<\/strong><\/p>\n
<\/strong>@Target annotation decided which type of elements can be marked by the annotation.<\/strong><\/p>\n
If the @Target is method and annotation is applied on any other element lets say class, then compiler will generate an error.<\/p>\n
The value attribute is one or more of the “java.lang.annotation.ElementType<\/em>” enum constants. Those constants are ElementType.ANNOTATION_TYPE, CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, PARAMETER, and TYPE.<\/p>\n","protected":false},"excerpt":{"rendered":"
What is Meta Annotation and its usage in JAVA<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"advanced_seo_description":"","jetpack_seo_html_title":"","jetpack_seo_noindex":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"jz_research_post":"","_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[3],"tags":[36],"class_list":["post-1676","post","type-post","status-publish","format-standard","hentry","category-java","tag-annotation"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack-related-posts":[{"id":1683,"url":"https:\/\/www.jitendrazaa.com\/blog\/java\/reading-and-writing-custom-annotation\/","url_meta":{"origin":1676,"position":0},"title":"Reading and Writing Custom Annotation","author":"Jitendra","date":"March 16, 2011","format":false,"excerpt":"Article on Reading and Writing Custom Annotation with example","rel":"","context":"In "JAVA"","block_context":{"text":"JAVA","link":"https:\/\/www.jitendrazaa.com\/blog\/category\/java\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":1655,"url":"https:\/\/www.jitendrazaa.com\/blog\/java\/introduction-to-annotation-in-java\/","url_meta":{"origin":1676,"position":1},"title":"Introduction to Annotation in JAVA","author":"Jitendra","date":"March 14, 2011","format":false,"excerpt":"Introduction to Annotation in JAVA","rel":"","context":"In "JAVA"","block_context":{"text":"JAVA","link":"https:\/\/www.jitendrazaa.com\/blog\/category\/java\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":1959,"url":"https:\/\/www.jitendrazaa.com\/blog\/java\/servlet\/create-servlet-using-annotation\/","url_meta":{"origin":1676,"position":2},"title":"Create Servlet using Annotation – Servlet 3.0","author":"Jitendra","date":"April 13, 2011","format":false,"excerpt":"Create the Servlet without any deployment descriptor. 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