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