_Object-oriented Tree Traversal with Tools.JJForester_ TobiasKuipers, JoostVisser *Abstract* We want to use the advanced language processing technology available in the Asf+Sdf Meta-Environment in combination with general purpose programming languages. In particular, we want to combine the syntax definition formalism SDF and the associated components that support Sdf.GeneralizedLR parsing, with the object-oriented language Java. To this end, we implemented Tools.JJForester, a tool that generates class structures from SDF grammar definitions. The generated class structures implement a number of _design patterns_ to facilitate construction and traversal of parse trees represented by object structures. In a detailed case study, we demonstrate how program analyses and transformations can be constructed with Tools.JJForester. http://www.cwi.nl/~jvisser/papers/JJForester.pdf