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We present algebraic laws for a language similar to a subset of sequential Java that includes inheritance, recursive classes, dynamic binding, access control, type tests and casts, assignment, but no sharing. These laws are proved sound with respect to a weakest precondition semantics. We also show that they are complete in the sense that they are sufficient to reduce an arbitrary program to a normal form substantially close to an imperative program; the remaining object-oriented constructs could be further eliminated if our language had recursive records. This suggests that our laws are expressive enough to formally derive behaviour preserving program transformations; we illustrate that through the derivation of provably-correct refactorings.

The Java Modeling Language (JML) is a behavioral interface specification language (BISL) designed for Java. It was developed to improve functional software correctness of Java applications. However, instrumented object program generated by the JML compiler use the Java reflection mechanism and data structures not supported by Java ME applications. To deal with this limitation, we propose the use of AspectJ to implement a new JML compiler, which generates an instrumented bytecode compliant with both Java SE and Java ME applications. The paper includes a comparative study to demonstrate the quality of the final code generated by our compiler. The size of the code is compared against the code generated by an existent JML compiler. Moreover, we evaluate the amount of additional code required to implement the JML assertions in Java applications. Results indicate that the overhead in code size produced by our compiler is very small, which is essential for Java ME applications.

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