Encapsulation, delegation and inheritance in object-oriented languages

For the reuse of software to become routine, it is essential that all modules have well defined interfaces and that all users of these modules respect these interfaces. The paper examines the interfaces in object-oriented programs. It uses the notion of delegation, which can be thought of as underlying all inheritance mechanisms, to provide a framework for the examination of encapsulation mechanisms in object-oriented languages. Using delegation, the encapsulation mechanisms in class-based languages are reviewed, and suggestions are made as to how they might be improved