Inheritance-Object Oriented Programming-Lecture Slides, Slides of Object Oriented Programming

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Object Orientedj

Programming using C++

Lecture – 8

Inheritance

Inheritance

Function A

Base Class Local Data

Function B

Local Data

Function A

Derived Class (^) Derived Class Local Data

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Function A Function B Function C, D

Function A

Local Data

Function B Function E

Function B Function F

Derived Class

Inheritance

„ A tool for reusability, such that new classes ,called derived classes, are created fromcalled derived classes are created from the existing ones, base classes „ Derived classes inherit the capabilities of their base classes, and can add their own „ Terminology

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‰ Base class (super-class) ‰ Derived class (sub-class)

Inheritance - Advantages

„ Reusability: ‰ H lHelps the code to be reused th d t b d ‰ Base classes are written and tested once, sort of standardized ‰ Derived classes inherit the attributes and behavior of the base class, and add their own specialties

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specialties ‰ No limit on the number of derived classes

Inheritance - Advantages

„ Saves time and money ‰ SS pecialization is only required in the derivedi li ti i l i d i th d i d class coding ‰ Where as base classes have been already standardized with much efforts „ Helps better structuring your program

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„ Increased reliability

Inheritance (contd..)

„ Example: „ In a 3D game engine, the code for ah d f character is written once with all its attributes and behavior ‰ Character’s shape ‰ Its walk

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‰ Jump ‰ Crawling ‰ Etc..

Inheritance (contd..)

„ All these properties can then be inherited by a specific character „ With required tweaks, it could be formed into a specialized character „ Finally, you can have as many objects of this character in your game, as you want

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Inheritance (contd..)

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Soldiers in CoD

Zombies in PoP

Inheritance

Specialization Vs. Generalization

CCar

Performance

Luxury Sports

ralization

Specializati

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Performance

Toyota Honda

Phantom Porche

Gener

on

Syntax

Base class

Derived class class derivedClass: public baseClass class baseClass { private: //private data of the base protected: //protected data of the base

{ //Derived class inherits all the //data of base class (except //private) private: //private data of the derived protected:

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public: //pubic data of the base };

protected: //protected data of the derived public: //pubic data of the derived };

Syntax (contd..) „ Colon in the declaration identifies that the class is inherited „ Colon is followed by a keyword (public in previous case) ‰ This identifies the access of the base class members using derived class’s objectderived class’s object ‰ E.g., void main() { derivedClass dObject; dObject.private_data; //Error dObject.public_data; //Okay d b bl d f b k

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dObject.public_data_of_base; //Okay

baseClass bObject; bObject.private_data; //Error bObject.public_data_of_base; //Okay }

Protected Access

„ So far, we have seen two access modes in C++C++ ‰ Public: „ Directly accessible by the users of a class ‰ Private: „ Not directly accessible by the users of a class, not even by the derived classes

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by the derived classes „ A third access mode ‰ Protected „ Directly accessible by the derived classes, but not by the users (objects)

Public and Private Derivation

private

When you don’t class A supply an access specifier, private is protected public

private private

class B : public A class c : private A

assumed

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protected public

protected public Object B (^) Object C

Object A

PUBLIC INHERITANCE

„ Public inheritance means that: ‰ public members of the base class become publicbli b f th b l b bli members of the derived class; ‰ protected members of the base class become protected members of the derived class; and ‰ private members of the base class are inaccessible within the derived class

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inaccessible within the derived class.

class Base { }; class Derived : public Base { };

PROTECTED INHERITANCE

„ Protected inheritance means that: ‰ public members of the base class becomebli b f th b l b protected members of the derived class; ‰ protected members of the base class become protected members of the derived class; and ‰ private members of the base class are inaccessible within the derived class

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inaccessible within the derived class.

class Base { }; class Derived : protected Base { };

PRIVATE INHERITANCE

„ Private inheritance means that: ‰ public members of the base class become privatebli b f th b l b i t members of the derived class; ‰ protected members of the base class become private members of the derived class; and ‰ private members of the base class are inaccessible within the derived class

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inaccessible within the derived class.

class Base { }; class Derived : private Base { };