C++ Inheritance

C++ Inheritance

• 1.
  Inheritance Jussi PohjolainenTAMK University of Applied Sciences
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  Introduction to InheritanceInheritance is a relationship between two or more classes where derived class inherites behaviour and attributes of pre-existing (base) classes Intended to help reuse of existing code with little or no modification
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  Inheritance Inheritance canbe continous Derived class can inherit another class, which inherits another class and so on When changing the base class all the derived classes changes also Example: Mammal <– Human <– Worker <- Programmer Could mammal be a derived class? If so, what would be the base class?
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  Picture about InheritanceC lass B F eatures: a,b,c C lass D F eatures: a,b,d,e,f a b C lass A features: a,b c d e C lass C F eatures: a,b,d,e f
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  Multiple Inheritance Inmultiple inheritance a derived class has multiple base classes C++ supports multiple base classes, Java don't Driver - license - Y ear of approval Conductor - A ccount number Taxi Driver - area House Boat Houseboat
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  Inheritance and Capsulationprivate Is accessible only via the base class public Is accessible everywhere (base class, derived class, othe classes) protected Is accessible by the base class and derived classes
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  Basic example Whatare Programmer's attributes and methods? Human string name void sleep() void drink() void eat() Programmer int salary void implementApps() void beNerd()
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  Overriding? What aboutnow? Human string name void sleep() void drink() void eat() Programmer int salary void implementApps() void beNerd() void drink() void eat()
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  Overriding Since programmereats and drinks differently than humans (only Coke and Pizza) the eat and drink methods are overriden in Programmer!
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  Abstract Class Abstractclass is a class which you cannot instantiate (create objects) You can inherit abstract class and create objects from the inherited class, if it is concrete one Abstract class in C++ has abstract methods, that do not have implementations These methods forces derived classes to implement those methods
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  Example <<abstract>> Mammalstring name void makesound() {abstract} Elephant int trunkLength makesound()
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  Example <<abstract>> Figureint x, y double calculateArea() {abstract} Circle double radius double calculateArea() Rect double length, height double calculateArea()
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  Exercises
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  INHERITANCE IN C++
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  Declaring Inheritance classCircle : public Figure { }
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  Declaring Inheritance classFigure { public: int x, y; }; class Circle : public Figure { public: int radius; }; int main() { Circle a; a.x = 0; a.y = 0; a.radius = 10; }
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  Encapsulation class Figure { protected : int x, y; }; class Circle : public Figure { public: int radius; }; int main() { Circle a; a.x = 0; a.y = 0; a.radius = 10; } example.cpp: In function ‘int main()’: example.cpp:5: error: ‘int Figure::x’ is protected example.cpp:17: error: within this context example.cpp:5: error: ‘int Figure::y’ is protected example.cpp:18: error: within this context
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  Encapsulation class Figure { protected: int x_, y_; }; class Circle : public Figure { private: int radius_; public: Circle(int x, int y, int radius); }; Circle::Circle(int x, int y, int radius) { x_ = x; y_ = y; radius_ = radius; } int main() { Circle a(0,0,10); }
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  Encapsulation class Figure { private : int x_, y_; }; class Circle : public Figure { private: int radius_; public: Circle(int x, int y, int radius); }; Circle::Circle(int x, int y, int radius) { x_ = x; y_ = y; radius_ = radius; } int main() { Circle a(0,0,10); } example.cpp: In constructor ‘Circle::Circle(int, int, int)’: example.cpp:5: error: ‘int Figure::x_’ is private example.cpp:18: error: within this context example.cpp:5: error: ‘int Figure::y_’ is private example.cpp:19: error: within this context
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  Encapsulation class Figure { private: int x_, y_; public: void SetX(int x); void SetY(int y); }; void Figure::SetX(int x) { x_ = x; } void Figure::SetY(int y) { y_ = y; } class Circle : public Figure { private: int radius_; public: Circle(int x, int y, int radius); }; Circle::Circle(int x, int y, int radius) { SetX(x); SetY(y); this->radius_ = radius; } int main() { Circle a(0,0,10); }
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  What is theresult? class Figure { public: Figure() { cout << &quot;Figure Constructor\n&quot;; } ~Figure() { cout << &quot;Figure Destructor\n&quot;; } }; class Circle : public Figure { public: Circle() { cout << &quot;Circle Constructor\n&quot;; } ~Circle() { cout << &quot;Circle Destructor\n&quot;; } }; int main() { Circle a; }
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  Inheritance and ConstructorsWhen creating a object from derived class, also the member values of the base class must be initialized Base constructor is called before the derived classes constructor Destructors vice versa.
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  Calling the BaseClasses constructor class Figure { public: Figure() { cout << &quot;Figure Constructor\n&quot;; } ~Figure() { cout << &quot;Figure Destructor\n&quot;; } }; class Circle : public Figure { public: Circle() : Figure() { cout << &quot;Circle Constructor\n&quot;; } ~Circle() { cout << &quot;Circle Destructor\n&quot;; } }; int main() { Circle a; }
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  Calling the BaseClasses constructor class Figure { private: int x_, y_; public: Figure(int x, int y) : x_(x), y_(y) { cout << &quot;Figure Constructor\n&quot;; } ~Figure() { cout << &quot;Figure Destructor\n&quot;; } };
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  Calling the BaseClasses constructor class Circle : public Figure { private: double radius_; public: Circle(int x, int y, int radius) : Figure(x, y), radius_(radius) { cout << &quot;Circle Constructor\n&quot;; } ~Circle() { cout << &quot;Circle Destructor\n&quot;; } }; int main() { Circle a(0,0,5); }
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  Abstract Class InC++, Abstract class is a class that has one abstract method Abstract method is a method without implementation. Abstract method is created by reserverd word &quot;virtual&quot;
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  Example of Abstractclass class Figure { private: int x_, y_; public: Figure(int x, int y) : x_(x), y_(y) { cout << &quot;Figure Constructor\n&quot;; } ~Figure() { cout << &quot;Figure Destructor\n&quot;; } virtual double calculateArea() = 0; };
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  Example of Abstractclass class Circle : public Figure { private: double radius_; public: Circle(int x, int y, int radius) : Figure(x, y), radius_(radius) { cout << &quot;Circle Constructor\n&quot;; } ~Circle() { cout << &quot;Circle Destructor\n&quot;; } double calculateArea() { return 3.14 * radius_ * radius_; } };
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  Example of Abstractclass int main() { Circle a(0,0,5); cout << a.calculateArea() << endl; // This Does not work, since figure is abstract: // Figure f(0,0); }