![]() ![]() Here is another annotation using most of the types above:Įnum AccessLevel ĪccessLevel accessLevel() default AccessLevel.PACKAGE_PROTECTED ![]() an array containing one of the above types.primitive types like int, long, double or boolean.The latter requirement is somewhat inconvenient and forces programmers to use other default values like “” or Void.class.Īdditionally, annotation elements cannot have arguments, cannot define thrown exceptions, cannot be generic and their element types are limited to: The default value must be a constant and can never be a null value. If it is not specified, the default value is used. If the element has a default value, it can but don’t have to be specified when using the annotation. It is, however, impossible to create a new annotation type by extending (inheriting from) existing annotation type.Īnother important difference is the ability to specify a default value for the annotation element. It is also possible to create static fields, static classes and enums inside an annotation. The similar syntax is not a coincidence because in fact annotations are visible to the virtual machine as plain interfaces extending Annotation interface and the annotation elements are visible as abstract methods. The most visible difference is the usage of interface keyword preceded by the at sign when defining annotation type. Creating custom annotationĪnnotation type definition is very similar to an interface definition: In this article I would like to describe how to create custom annotations and later access them through reflection. Of course, the list is not even one percent complete. For example many Java frameworks define custom annotations to provide (or at least simplify usage of) such functionality as: Java developers are not limited to using built-in annotations only but can also create their own annotations to provide additional functionality. ![]()
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