Design Pattern Refactoring by Pretty-Printing

Most design patterns in the Gang-of-Four text can be written as a refactoring script – a programmatic sequence of refactorings.R is a new Java refactoring engine based on prettyprinting. It builds a main-memory, non-persistent database to encode containment relationships among Java entity declarations (e.g., packages, classes, methods), language features such as inheritance and modifiers, and precondition checks for each declaration. R design pattern scripts modify the database and do not modify Abstract Syntax Trees (ASTs). While classical refactoring engines transform source code or ASTs directly, R produces refactored code by displaying the contents of the modified database when pretty-printing ASTs. R performs comparable precondition checks and code changes to that of the Eclipse Java Development Tools (JDT) refactorings but R’s codebase is about half the size of JDT refactorings and runs an order of magnitude faster. R refactorings pass relevant regression tests in JDT and fix JDT refactoring bugs that we found.