Composition over inheritance

Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should achieve polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) rather than inheritance from a base or parent class. This is an often-stated principle of OOP, such as in the influential book Design Patterns.While there is not huge opportunity to replace inheritance with composition (...), the opportunity is significant (median of 2% of uses are only internal reuse, and a further 22% are only external or internal reuse).Our results suggest there is no need for concern regarding abuse of inheritance (at least in open-source Java software), but they do highlight the question regarding use of composition versus inheritance. If there are significant costs associated with using inheritance when composition could be used, then our results suggest there is some cause for concern. Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should achieve polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) rather than inheritance from a base or parent class. This is an often-stated principle of OOP, such as in the influential book Design Patterns. An implementation of composition over inheritance typically begins with the creation of various interfaces representing the behaviors that the system must exhibit. Interfaces enable polymorphic behavior. Classes implementing the identified interfaces are built and added to business domain classes as needed. Thus, system behaviors are realized without inheritance.