Encapsulation and inheritance in object-oriented programming languages

Object-oriented programming is a practical and useful programming methodology that encourages modular design and software reuse. Most object-oriented programming languages support data abstraction by preventing an object from being manipulated except via its defined external operations. In most languages, however, the introduction of inheritance severely compromises the benefits of this encapsulation. Furthermore, the use of inheritance itself is globally visible in most languages, so that changes to the inheritance hierarchy cannot be made safely. This paper examines the relationship between inheritance and encapsulation and develops requirements for full support of encapsulation with inheritance.