Object Oriented Programming - C++

Inheritance - C++

Inheritance is the ability of a class to inherit features of one or more other classes. That is, inheritance is achieved by creating a new or derived class from at least one exisiting class. The existing class sometimes is called the base class, and the new class is called the derived class.

Inheritance pertains to class, and not to ordinary non-class variables and functions. In practice programs do inherit. For example, programs inherit windows, screens, and such gadgets. In an integrated environment the main screen for a Spreadsheet is thesame across the board for the Wordprocessor and the Database programs. This comes as result of one application inheriting features that they have in common.

Charateristics of Inheritance

• Base class - the class from which a new class is derived
• The derived class inherits members from the base class
• The derived class may add to its inheritance
• Private members of the base class remains private to the base class
• Added functions of the derived class cannot have access to any of the private members of the base class
• Private members of the base class may be accessed by member functions that were inherited from the base class

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Base and Derived Classes
As was mentioned, inheritance is achieved by creating a new or a derived class from at least one exisiting class. The format for class derivation follows the following pattern:

class Derived: access_specifier Base1, access_specifier Base2, …. {
// Code for the derived class };

Access specifier can either be:

• private, where private members that are derived from the base class remains private to the base class
• protected, where members of the derived class can have access to protected members of the base class, or
• public, where members of the derived class can have access to public members of the base class.

Analysis

• If a derived class needs to access a private data member of the base class, change that private member to a protected member of the base class.
• Neither main nor any non-member function can have access to either private members or protected members·
• There can be multiple inheritances from a base class
• There can be heirarchy of inheritances
• Constructors and destructors are not inherited
• Each derived class must provide its own constructors and destructors
• The order in which the constructors are called match the order in which they are specified in the derived class' inheritance list.
• The destructors are called in the reverse order of how the constructors were called
• A derived class' constructor arguments can be passed to base class constructor

Demonstrations Programs

Inheritance I: Introduction

Inheritance II:Private vs Public Members

Inheritance III Protected Members

Inheritance IV Constructors and Destructors

Inheritance IV class: A Data Type

Inheritance IV Derived class initializes Base class constructor

Inheritance I: Go Back to the Schedule