Nil or export coupling only

Classes should only exhibit nil or export coupling with other classes, i.e. a class should only use operations in the public interface of another class or have nothing to do with that class Riel's Heuristic 2.7, Arthur Riel 1996

Classes should only depend on the public methods of another class or nothing at all. Other forms of coupling give away implementation details of a class, which is bad for maintenance when implementations need to be changed.

Riel also states that class cohesion ensures that all elements of a class are related.

See also

• Riel's heuristics
• Program to the interface not the implementation
• Design by contract