Aspect Oriented Programming (AOP) - AspectJ

http://www.voelter.de/data/articles/aop/aop.html

Object oriented programming has become mainstream over the last years, having almost completely replaced the procedural approach. One of the biggest advantages of object orientation is that a software system can be seen as being built of a collection of discrete classes. Each of these classes has a well defined task, its responsibilities are clearly defined. In an OO application, those classes collaborate to achieve the application's overall goal. However, there are parts of a system that cannot be viewed as being the responsibility of only one class, they cross-cut the complete system and affect parts of many classes. Examples might be locking in a distributed application, exception handling, or logging method calls. Of course, the code that handles these parts can be added to each class separately, but that would violate the principle that each class has well-defined responsibilities. This is where AOP comes into play: AOP defines a new program construct, called an aspect, which is used to capture cross-cutting aspects of a software system in separate program entities. The application classes keep their well-defined responsibilities. Additionally, each aspect captures cross-cutting behaviour.