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How and where are Annotations used in Java?
Java beans, annotations: What do they do? How do they help me?
Over and over, I read about Java 5's annotations being an 'advanced feature' of the language. Until recently, I haven't much used annotations (other than the usual @Override, &c), but work on a number of webservice-related projects has forced my hand. Since I learned Java pre-5, I never really took the time to sit down and grok the annotation system.
My question- do you guys actually use annotations? How helpful are they to you, day-to-day? How many StackOverflow-ers have had to write a custom annotation?
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It is also possible to use multiple annotations on the same declaration: @Author(name = "Jane Doe") @EBook class MyClass { ... } If the annotations have the same type, then this is called a repeating annotation: @Author(name = "Jane Doe") @Author(name = "John Smith") class MyClass { ... }
It is now possible to use an annotation zero times, once, or, if the annotation's type is marked as @Repeatable , more than once. It is also possible to restrict where an annotation type can be used by using the @Target meta-annotation.
Repeatable Annotation: The Repeating Annotation has to be annotated with @Repeatable to have the capability to repeat. We have to pass the class name as a parameter to the meta-annotation @Repeatable where the compiler can store all the multiple annotations and that acts as a container for values.
Annotations are used to provide supplemental information about a program. Annotations start with '@'. Annotations do not change the action of a compiled program. Annotations help to associate metadata (information) to the program elements i.e. instance variables, constructors, methods, classes, etc.
Perhaps the most useful and used case of Java Annotations is to use POJO + Annotation instead of xml configuration files
I use it a lot since (as you already stated) if you use a web framework (like spring or seam) they usually have plenty of annotations to help you.
I have recently wrote some annotations to build a custom statemachine, validations purpose and annotations of annotations (using the metadata aspect of it). And IMO they help a lot making the code cleaner, easier to understand and manage.
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