AspectJ is a simple and practical aspect-oriented extension to Java. With just a few new constructs, AspectJ provides support for modular implementation of a range of crosscutting concerns.

Adoption of AspectJ into an existing Java development project can be a straightforward and incremental task. One path is to begin by using only development aspects, going on to using production aspects and then reusable aspects after building up experience with AspectJ. Adoption can follow other paths as well. For example, some developers will benefit from using production aspects right away. Others may be able to write clean reusable aspects almost right away.

AspectJ enables both name-based and property based crosscutting. Aspects that use name-based crosscutting tend to affect a small number of other classes. But despite their small scale, they can often eliminate significant complexity compared to an ordinary Java implementation. Aspects that use property-based crosscutting can have small or large scale.

Using AspectJ results in clean well-modularized implementations of crosscutting concerns. When written as an AspectJ aspect the structure of a crosscutting concern is explicit and easy to understand. Aspects are also highly modular, making it possible to develop plug-and-play implementations of crosscutting functionality.

AspectJ provides more functionality than was covered by this short introduction. The next chapter, The AspectJ Language, covers in detail more of the features of the AspectJ language. The following chapter, Examples, then presents some carefully chosen examples that show you how AspectJ might be used. We recommend that you read the next two chapters carefully before deciding to adopt AspectJ into a project.