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Java annotations can be added to program elements such as classes, methods, fields, parameters, local variables, and packages. Unlike tags added to Java documentation and processed with tools such as [[XDoclet]], Java annotations are completely accessible to the programmer while the software is running using [[reflection (programming)|reflection]].
==History
Java annotations were introduced to the [[Java Community Process]] as JSR-175 in [[2002]] and approved in September [[2004]]. Annotations became available with the [[JDK]] version 1.5. The feature was added to the Java language through the specification.
==Processing==
When Java source code is compiled, the Java compiler stores annotation metadata in the class files. Later, the [[JVM]] or other programs can look for the metadata to determine how to interact with the program elements or change their behavior.
==Syntax
Declaring an annotation is a variation on tags that have been added to comment sections in the past.
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In the above example both Retention and Target are examples of annotations.
==Impact and Perception==
===Pros===
Annotations allow the programmer to declare in their source code how the software should behave. It is an example of how declarative programming constructs can be added to a procedural language.
===Cons===
* Adding metadata to a run time causes additional memory overhead.
* There are few standards that dictate what metadata tags should be used
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