Superimpositions and Aspect-oriented Programming

The ideas of a classic distributed superimposition are used to design a new object-oriented version incorporating aspects. A superimposition is a collection of generic parameterized aspects and new classes (often singleton concrete classes). Superimpositions can be combined, either sequentially or in a merge, to create new ones. Superimpositions also include specifications about assumed properties of basic programs to which the superimposition can be applied and desired properties added by the superimposition. These specifications are used to define proof obligations for the correctness of superimpositions and to check feasibility of combining superimpositions. SuperJ, a notation and an implemented preprocessor over AspectJ, is described. SuperJ can be used to apply a superimposition to a basic system, generating concrete aspects from generic aspects and then weaving them to basic classes. Superimpositions are separately declared, specified and verified. Among the examples used to demonstrate the approach are a termination detection algorithm, a version of the Dining Philosophers Problem and a monitoring superimposition that gathers statistics on basic objects.