Inheritance in C .1

8/13/2019 Inheritance in C .1

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Inheritance in C++

[email protected]


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Three types of Inheritance in C++

Public inheritance - Inheritance for extension

Private inheritance andprotected inheritance - Inheritance

for restriction


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Syntax inheritance in C++

Public Inheritance (Inheritance for Extension)

Equivalent to Manager extends Employee in Java


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Public Inheritance in C++ Users View

Same as Java extends

Interface of Derived class objects is super set of baseclass objects

Interface ( Derived ) =Interface (Base) U Interface (added in derived class)

Derived class objects are subtype of base class, i.e., theycan substitute base class objects


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Users View of Private Inheritance in C++

(Inheritance for Restriction)

Interface of Derived class objects is subset of base classobjects

IMP: derived class objects are not subtype of base class,therefore, they can not substitute base class objects

Note: java does not support this type of inheritance


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Implementation View of various Inheritance types

in C++


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Protected Visibility in C++

Protected members are as good as private except thatthese are seen by derived classes, that means

Protected members can not be accessed by methods ofother class, unless other class is derived class (or friend

class)


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Implementation View of

Public Inheritance in C++

Same as Java extends

Public members are inherited as public

Private fields are inherited but can not be accessed byderived class methods

Private methods are not inherited

Protected are inherited and have protected visibility inderived class


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Public Inheritance If inheritance is public then, class

B inherits as following - x is inaccessible in it

xp, and getXP() as protected

getX() as public


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Private Inheritance - Inheritance for restriction

Public members are inherited as private

Private fields are inherited but can not be accessed by

derived class methods


Protected are inherited as private


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Private Inheritance

If inheritance is private then B

inherits x is inaccessible in it

xp, and getXP() as private

getX() as private


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Protected Inheritance Inheritance for restriction

Public members are inherited as protected in derived class

Private fields are inherited but can not be accessed by

derived class methods


Protected are inherited as protected


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Protected Inheritance

If inheritance is protected then B

inherits x is inaccessible in it

xp, and getXP() as protected

getX() as protected


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Type Substitution in C++

In C++, type substitution has two variations-

Object Substitution: When object of subtype

substitutes objects of super-type

Reference Substitution: When pointer (or reference) of

base type refers to objects of subtype


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Consider classes- Manager public inherits Employee


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Object Substitution

Considering code below-

Employee e("Sumit Mehta", 45000.00);Manager m("Anil",50000.00,"Marktg");

m.setBonus( 5000 );

Employee x = m;

It is object substitution- however there is loss of data insuch assignments, known as object slicing problem in

C++ ? Also, guess, what will happen if you write e = m ?

Note: Type Substitution works only when you have inheritance forextension, i.e. have public inheritance


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Reference Substitution

Consider object m of previous example, following is

example of reference substitution (pointer of base typerefers to objects of subtype) -

Employee* x = &m;

In this case, there is no object slicing, since object is

intact, only the thing, pointer is of super type same as in

Java


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Method Binding

In case of Object Substitution, it is always static

In fact object substitution is a copying data from subtype

object to super type object

In the example here, x.getSalary() will be bound to

Employee::getSalary(), where as m.getSalary would bebound to Manager::getSalary(), after all x and m are two

different objects of two different types ?


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Questions


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Thanks

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Inheritance in C .1