Ja TS

Program-Transformation.Org: The Program Transformation Wiki

Transformation system for the Java programming language.

Program transformation is a powerful technique for supporting software engineering activities: refactoring, formal software development, code generation and language translation.

In fact, refactoring, the process of restructuring code with the purpose of making it easier to understand and maintain without changing its observable behavior, is strongly coupled with program transformation. Refactorings can be specified as parameterized program transformations that obey behavior-preserving preconditions. Nowadays, the use of refactoring to increase quality is considered a very important development practice. For instance, Extreme Programming , a approach for software development, recommends the use of refactoring as a continuous activity, intimately related to coding. Formal and rigorous software development methods are strong candidates to the use of program transformation as well, since refinement laws can be easily described as program transformations satisfying preconditions that guarantee the soundness of the refinement. This is the case for imperative languages, as in the refinement calculus, but also for object oriented languages. In both cases, algebraic laws for programming languages can be viewed and implemented as program transformations.

Those applications of program transformation show its importance, but its use in practical, large scale, projects is not possible without automation. Tool support is vital to the application of program transformations, in order to provide productivity and eliminate the danger of introducing errors, when performing such a tedious and demanding task. Several program transformation tools have been implemented. Many of these are not language specific, being able to transform programs from an arbitrary source language to an arbitrary destination language. Although this may be an advantage, it complicates the use of the tools, since they require two kinds of user: the transformation engineer, who configures the tool (encodes the transformations) and the programmer, who uses the tool for software development (applies the transformations). This is usually necessary because, in most cases, the language in which the transformations are encoded is substantially different from the one to which they are applied.

There are also language-specific tools for program transformation. Most of these have the drawback of supporting only a fixed set of built-in transformations. For instance, refactoring systems usually implement a few simple refactorings that can be applied, but a programmer cannot add a new refactoring to this tool, unless he has access to the source code of the system. Formal software development systems are usually similar: they support a set of built-in refinement laws that cannot be extended.

In order to avoid the drawbacks of the general purpose and language-specific transformation tools, we present a language to specify program transformations for the Java programming language. In this language, transformations are specified using a superset of Java, making it easier for programmers to specify the transformations they wish to apply and thus eliminating the need for the transformation engineer. Also, it takes the semantics of Java into account, making it possible to implement transformations that could not be implemented if only the syntax was taken into account. The language has been named JaTS, an acronym for Java Transformation System, the system that actually implements this language and applies transformations to Java programs.