Annotations are used to provide supplemental information about a program.
- Annotations starts with @
- Annotation do not change the action of a compiled program
- Annotations helps to associate metadata to the program elements.(i.e) instant varibale,method,constructor,class etc.
- Annotations are basically used to provide additional information
Types of Annotations
- Built in Annotations (General purpose annotations & meta annotations)
- Custom Annotation
Built in Annotations
Java popularly defines seven built in annotations
Four are imported from java.lang.annotation:
- @Retention,
- @Documented,
- @Target,
- @Inherited.
Three are included in java.lang:
- @Deprecated,
- @Override,
- @SuppressWarnings.
Example
1)@override
It is a marker annotation that can be used only on methods. A method annotated with @Override must override a method from a superclass.
Program
Output:
Moon girl
2) @Deprecated
- It is a marker annotation. It indicates that a declaration is obsolete and has been replaced by a newer form
- @deprecated tag is for documentation and @Deprecated annotation is for runtime reflection
- @deprecated tag has higher priority than @Deprecated annotation when both are together used
Example
Output
Deprecatedtest display();
Categories of Annotations
1)Marker Annotations
- The only purpose is to mark a declaration
- @Override is an example of Marker Annotation.
- Syntax: @TestAnnotations( )
2)Single value Annotations
- These annotations contain only one member and allow a shorthand form of specifying the value of the member.
- Syntax: @TestAnnotations(“testing”);
3)Full Annotations
- These annotations consist of multiple data members, names, values, pairs
- Syntax: @TestAnnotations(name=”Moon”,value=”…”)
4)Type Annotations
- These annotations can be applied to any place where a type is being used. For example, we can annotate the return type of a method.
- These are declared annotated with @Target annotation.
5)Repeating Annotations
- These are the annotations that can be applied to a single item more than once.
- For an annotation to be repeatable it must be annotated with the @Repeatable annotation, which is defined in the java.lang.annotation package
Custom Annotations
Java Custom annotations or Java User-defined annotations are easy to create and use. The @interface element is used to declare an annotation
Example:
@interface Myannotation{
}
