Table of contents

annotations

declaring an annotation

@interface ClassPreamble {
   String author();
   String date();
   int currentRevision() default 1;
   String lastModified() default "N/A";
   String lastModifiedBy() default "N/A";
   String[] reviewers();
}

annotation annotations

annotation can be inherited from its superclass

@Inherited

meta annotation that includes annotated annotation in the javadoc

@Documented

target

specify which java elements may have the annotation

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Menu {
	String text();
}

target types

ElementType.ANNOTATION_TYPE		annotation type
ElementType.CONSTRUCTOR			constructor
ElementType.FIELD				field or property
ElementType.LOCAL_VARIABLE		local variable
ElementType.METHOD				method-level annotation
ElementType.PACKAGE				package declaration
ElementType.PARAMETER			parameters of a method
ElementType.TYPE				element of a class

retention

setting the retention policy of an annotation

@Retention(RetentionPolicy.RUNTIME)
@Inherited
public @interface Immutable {
}

available retention policies

RetentionPolicy.SOURCE     only in source; ignored by the compiler
RetentionPolicy.CLASS      retained by the compiler at compile time, but ignored by the JVM
RetentionPolicy.RUNTIME    retained by the JVM; can be used by the runtime environment

repeatable

annotation can be repeated

/* container annotation for backwards compatibility */
public @interface Imports {
	Import[] value();
}

@Repeatable(Imports.class)
public @interface Import {
	String value();
}