Inheritance

A new class may be derived from an existing class.
- The new class is called the derived class or the subclass.
- The other class is called the base class or the superclass.
- The subclass has its own data members and member functions.
- The subclass inherits all the data members and member functions of the base class.
The HAS_A Relation
- If an object of class A has a component that is an object of class B, then the HAS_A relation holds from class A to class B.
- Example:
  - A Car has an Engine.
  - The HAS_A relation holds from class Car to class Engine.
- If every class A object HAS_A class B component, then an object of class B should be a data member of class A.
The IS_A Relation
- If an object of class A is an object of a more general class B, then the IS_A relation holds from class A to class B.
- Example:
  - A Car is a Vehicle.
  - The IS_A relation holds from class Car to class Vehicle.
- If every class A object IS_A class B object, then class A should be derived as a subclass of class B.
The IS_A relation is transitive.
- If a FordMustang IS_A Car and a Car IS_A Vehicle, then a FordMustang IS_A Vehicle.
Class inheritance is transitive.
- If class B is a subclass of class A and class C is a subclass of class B, then class C is a subclass of class A.
- Class C inherits data members and member functions from classes A and B.
Examples
- Header files
  - person.h (original), person.h (copy),
  - man.h (original), man.h (copy),
  - woman.h (original), woman.h (copy),
  - father.h (original), father.h (copy),
  - mother.h (original), mother.h (copy),
  - marriedman.h (original), marriedman.h (copy),
  - marriedwoman.h (original), marriedwoman.h (copy),
- Programs

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This page was last modified on Mar 1, 2001

URL: http://people.hsc.edu/faculty-staff/robbk/Coms262/Lectures/Inheritance.html