The primary claimed benefits of aspect-oriented programming (AOP) are that it improves the understandability and maintainability of software applications by modularizing crosscutting concerns. Before there is widespread adoption of AOP, developers need further evidence of the actual benefits as well as costs. Applying AOP techniques to refactor legacy applications is one way to evaluate costs and benefits. We replace crosscutting concerns with aspects in three industrial applications to examine the effects on qualities that affect the maintainability of the applications. We study several revisions of each application, identifying crosscutting concerns in the initial revision and also crosscutting concerns that are added in later revisions. Aspect-oriented refactoring reduced code size and improved both change locality and concern diffusion. Costs include the effort required for application refactoring and aspect creation, as well as a decrease in performance.

Moving program code that implements cross-cutting concerns into aspects can improve the maintainability of legacy systems. This kind of refactoring, called aspectualization, can also introduce faults into a system. A test driven approach can identify these faults during the refactoring process so that they can be removed. We perform systematic testing as we aspectualize commercial VLSI CAD applications. The process of refactoring these applications revealed the kinds of faults that can arise during aspectualization, and helped us to develop techniques to reduce their occurrences