Scripting parametric refactorings in Java to retrofit design patterns

Retrofitting design patterns into a program by hand is tedious and error-prone. A programmer must distinguish refactorings that are provided by an Integrated Development Environment (IDE) from those that must be realized manually, determine a precise sequence of refactorings to apply, and perform this sequence repetitively to a laborious degree. We designed, implemented, and evaluated Reflective Refactoring (R²), a Java package to automate the creation of classical design patterns (Visitor, Abstract Factory, etc.), their inverses, and variants. We encoded 18 out of 23 Gang-of-Four design patterns as R² scripts and explain why the remaining are inappropriate for refactoring engines. We evaluate the productivity and scalability of R² with a case study of 6 real-world applications. In one case, R² automatically created a Visitor with 276 visit methods by invoking 554 Eclipse refactorings in 10 minutes - an achievement that could not be done manually. R² also sheds light on why refactoring correctness, expressiveness, and speed are critical issues for scripting in next-generation refactoring engines.