Attribute-oriented programming (@OP) is a program-level marking technique. Programmers can mark program elements (e.g. classes and methods) to indicate that they maintain application-specific or domain-specific semantics. For example, some programmers may define a "logging" attribute and associate it with a method to indicate the method should implement a logging function, while other programmers may define a "web service" attribute and associate it with a class to indicate the class should be implemented as a web service. Attributes separate application's core logic (or business logic) from application-specific or domain-specific semantics (e.g. logging and web service functions). By hiding the implementation details of those semantics from program code, attributes increase the level of programming abstraction and reduce programming complexity, resulting in simpler and more readable programs. The program elements associated with attributes are transformed to more detailed programs by a supporting tool (e.g. preprocessor). For example, a preprocessor may insert a logging program into the methods associated with a "logging" attribute.
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Java
With the inclusion of The Metadata Facility for the Java Programming Language (JSR-175) into the J2SE 5.0 release it is possible to utilize attribute-oriented programming right out of the box. XDoclet library makes it possible to use attribute-oriented programming approach in earlier versions of Java.
C#
The C# language has supported attributes from its very first release. However these attributes are used to give run-time information and are not used by a pre-processor (there isn't one in C#'s reference implementation).
UML
The Unified Modeling Language (UML) supports a kind of attribute named Stereotypes.