AspectJ is a seamless aspect-oriented extension to the Java programming language, Java platform compatible and easy to learn and use. AspectJ enables the clean modularization of crosscutting concerns such as: error checking and handling, synchronization, context-sensitive behavior, performance optimizations, monitoring and logging, debugging support, multi-object protocols.
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Aspect-oriented programming is a way of modularizing crosscutting concerns much like object-oriented programming is a way of modularizing common concerns. AspectJ is an implementation of aspect-oriented programming for Java.
AspectJ adds to Java just one new concept, a join point -- and that's really just a name for an existing Java concept. It adds to Java only a few new constructs: pointcuts, advice, inter-type declarations and aspects. Pointcuts and advice dynamically affect program flow, inter-type declarations statically affects a program's class hierarchy, and aspects encapsulate these new constructs.
A join point is a well-defined point in the program flow. A pointcut picks out certain join points and values at those points. A piece ofadvice is code that is executed when a join point is reached. These are the dynamic parts of AspectJ.
AspectJ also has different kinds of inter-type declarations that allow the programmer to modify a program's static structure, namely, the members of its classes and the relationship between classes.
AspectJ's aspect are the unit of modularity for crosscutting concerns. They behave somewhat like Java classes, but may also include pointcuts, advice and inter-type declarations.
