Class hierarchy

A class hierarchy or inheritance tree in <a href="/facts/Computer_science/lN3pEyPz">computer science</a> is a classification of <a href="/facts/Object_(computer_science)/eX99dtAw">object</a> types, denoting objects as the instantiations of <a href="/facts/Class_(computer_programming)/zvzkSAtE">classes</a> (class is like a blueprint, the object is what is built from that blueprint) inter-relating the various classes by relationships such as "inherits", "extends", "is an abstraction of", "an interface definition". In <a href="/facts/Object-oriented_programming/TxNMEcao">object-oriented programming</a>, a class is a template that defines the state and behavior common to objects of a certain kind. A class can be defined in terms of other classes.
The concept of class hierarchy in computer science is very similar to <a href="/facts/Taxonomy_(biology)/Qkg8wuyw">taxonomy</a>, the classifications of species. 
The relationships are specified in the science of <a href="/facts/Object-oriented_design/erWk0mUW">object-oriented design</a> and object interface standards defined by popular use, language designers (<a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a>, <a href="/facts/C%2B%2B/Et0F2qn9">C++</a>, <a href="/facts/Smalltalk/Ru2UPVDE">Smalltalk</a>, <a href="/facts/Visual_Prolog/03tnjaK8">Visual Prolog</a>) and standards committees for software design like the <a href="/facts/Object_Management_Group/SNpN8n9U">Object Management Group</a>.
The class hierarchy can be as deep as needed. The instance variables and methods are inherited down through the levels and can be redefined according to the requirement in a subclass. In general, the further down in the hierarchy a class appears, the more specialized its behavior. When a message is sent to an object, it is passed up the inheritance tree starting from the class of the receiving object until a definition is found for the method. This process is called upcasting.

Class hierarchy open-in-new

Class hierarchy