1 / 32

Inheritance

Inheritance. Reference: Chapter 7. Inheritance Terminology. inheritance hierarchy “is a” relationship base class (superclass) derived class (subclass) class member access specifiers public protected private abstract class member function overriding member slicing

murray
Download Presentation

Inheritance

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Inheritance Reference: Chapter 7

  2. Inheritance Terminology • inheritance hierarchy • “is a” relationship • base class (superclass) • derived class (subclass) • class member access specifiers • public • protected • private • abstract class • member function overriding • member slicing • multiple inheritance

  3. Class Access Specifiers • Public • Member functions • Friend functions • Non-friend functions • Protected • Member functions • Friend functions • Private • Member functions • Friend functions

  4. Class Access Specifiers (continued) • Why Use Protected? • Allows derived classes to use member functions and data • items directly (don’t need to use base class accessor methods) • Still hides these member functions and data items from • non-friend functions • Watch Out! • Using “Protected” violates encapsulation! • If the protected members are changed in the base class, • it may affect the derived class code • New derived classes will have access to the protected • members • Use only in “emergency” situations

  5. Types of Inheritance • Public • The most common type • Protected • Rare • Private • Rare

  6. Public Inheritance • Specified by: • class name: public base-class-name • Inheritance: • public in base class, public in derived class • protected in base class, protected in derived class • private in base class, not accessible in derived class • (must use public or protected base class accessor methods) • By far, the most common type of inheritance.

  7. Protected Inheritance • Specified by: • class name: protected base-class-name • Inheritance: • public in base class, protected in derived class • protected in base class, protected in derived class • private in base class, not accessible in derived class • (must use public or protected base class accessor methods) • Rarely used.

  8. Private Inheritance • Specified by: • class name: private base-class-name • Inheritance: • public in base class, private in derived class • protected in base class, private in derived class • private in base class, not accessible in derived class • (must use public or protected base class accessor methods) • Rarely used.

  9. Public Inheritance Example class Time { public: Time(int h = 0, int m = 0, int s = 0); // cannot be inherited void set(int h, int m, int s); // overriden to set zone void increment(); // inherited void write() const; // overriden to print zone private: int hrs, mins, secs; }; // all data members inherited class ExtTime: public Time { public: ExtTime(int h = 0, int m = 0, int s = 0, ZoneType z = EST); void set(int h, int m, int s, ZoneType z); void write() const; private: ZoneType zone; }; // new data member

  10. Public Inheritance Example Using Protected class Time { public: Time(int h = 0, int m = 0, int s = 0); // cannot be inherited void set(int h, int m, int s); // overriden to set zone void increment(); // inherited void write() const; // overriden to print zone protected: // ENCAPSULATION VIOLATION! int hrs, mins, secs; }; // all data members inherited class ExtTime: public Time { public: ExtTime(int h = 0, int m = 0, int s = 0, ZoneType z = EST); void set(int h, int m, int s, ZoneType z); void write() const; private: ZoneType zone; }; // new data member

  11. Time Class Code #include <iostream.h> #include "time.H" Time::Time(int initHrs, int initMins, int initSecs) : hrs(initHrs), mins(initMins), secs(initSecs) { } void Time::Set(int hours, int minutes, int seconds) { hrs = hours; mins = minutes; secs = seconds; }

  12. Time Class Code (continued) void Time::Increment() { secs++; if (secs > 59) { secs = 0; mins++; if (mins > 59) { mins = 0; hrs++; if (hrs > 23) hrs = 0; } } }

  13. Time Class Code (continued) void Time::Write() const { if (hrs < 10) cout << '0'; cout << hrs << ':'; if (mins < 10) cout << '0'; cout << mins << ':'; if (secs < 10) cout << '0'; cout << secs; }

  14. Extended Time Class Code (Public Inheritance) #include <iostream.h> #include "exttime.H" ExtTime::ExtTime(int initHrs, int initMins, int initSecs, ZoneType initZone) : Time(initHrs, initMins, initSecs) { zone = initZone; } void ExtTime::Set(int hours, int minutes, int seconds, ZoneType timeZone) { Time::Set(hours, minutes, seconds); zone = timeZone; }

  15. Extended Time Class Code (continued) void ExtTime::Write() const { static char zoneString[8][4] = { "EST", "CST", "MST", "PST", "EDT", "CDT", "MDT", "PDT" }; Time::Write(); cout << ' ' << zoneString[zone]; }

  16. Operations on Base and Derived Class Objects • Time t(10, 5, 0); • ExtTime et(20, 15, 10, EST); • A derived class object can be assigned to a base class • object • t = et; // legal • Member slicing occurs. • A base class object cannot be assigned to a derived class • object • et = t; // illegal! Not all data members can be filled

  17. Operations on Base and Derived Class Objects (continued) • Time t(10, 5, 0); • ExtTime et(20, 15, 10, EST); • A base class pointer can point to a base class object • Time tPtr = &t; • A dervied class pointer can point to a derived class object • ExtTime etPtr = &et; • A base class pointer can point to a derived class object • Time tPtr = &et; // legal, but can only access base class data • members • A derived class pointer cannot point to a base class object • ExtTime etPtr = &t; // illegal!

  18. Sample Program Using Time and Extended Time Code: #include <iostream.h> #include "exttime.H" void main() { Time t1, t2(15, 10, 5); cout << "Instantiation of t1 = "; t1.Write(); cout << endl; cout << "Instantiation of t2 = "; t2.Write(); cout << endl; Output: Instantiation of t1 = 00:00:00 Instantiation of t2 = 15:10:05

  19. Sample Program Using Time and Extended Time Code: ExtTime et1, et2(30, 25, 20, CST); cout << "Instantiation of et1 = "; et1.Write(); cout << endl; cout << "Instantiation of et2 = "; et2.Write(); cout << endl; Output: Instantiation of et1 = 00:00:00 EST Instantiation of et2 = 30:25:20 CST

  20. Sample Program Using Time and Extended Time Code: et1.Set(50, 45, 40, MDT); cout << "et1 after Set(50, 45, 40, MDT) = "; et1.Write(); cout << endl; Output: et1 after Set(50, 45, 40, MDT) = 50:45:40 MDT

  21. Sample Program Using Time and Extended Time Code: // Set and display an extended time using base class Set // Should invoke base class Set, but get a compiler error // that the 4th parameter (zone) is missing. Should be an // overload, but compiler sees it as an override. // // et1.Set(70, 65, 60); // cout << "et1 after base class Set = "; // et1.Write(); cout << endl;

  22. Sample Program Using Time and Extended Time Code: // Mixing base and derived class objects t1 = et1; // Base class = derived class is legal cout << "t1 after t1=et1: "; t1.Write(); cout << endl; // et2 = t1; // Derived class = base class illegal -- syntax error! Output: t1 after t1=et1: 50:45:40

  23. Sample Program Using Time and Extended Time Code: // Mixing base and derived class pointers Time *tPtr; ExtTime *etPtr; // Base class pointer pointing to base class object tPtr = &t1; // 50, 45, 40 cout << "tPtr=&t1, tPtr->Write() = "; tPtr->Write(); cout << endl; // Dervied class pointer pointing to derived class object etPtr = &et2; // 30, 25, 20, CST cout << "etPtr=&et2, etptr->Write() = "; etPtr->Write(); cout << endl; Output: tPtr=&t1, tPtr->Write() = 50:45:40 etPtr=&et2, etptr->Write() = 30:25:20 CST

  24. Sample Program Using Time and Extended Time Code: // Base class pointer pointing to derived class object tPtr = &et2; // 30, 25, 20, CST cout << "tPtr=&et2, tPtr->Write() = "; tPtr->Write(); cout << endl; // Try to access a derived class method // tPtr->WriteZone(); // illegal -- syntax error! // Derived class pointer pointing to base class object // etPtr = &t1; // illegal -- syntax error! Output: tPtr=&et2, tPtr->Write() = 30:25:20

  25. Constructors and Destructors in Derived Classes • Base class constructors are not inherited by derived classes • A derived class’ constructor must invoke its base class’ • constructor (or use its base class’ default constructor) • ExtTime::ExtTime(int initHrs, int initMins, int initSecs, • ZoneType initZone) : • Time(initHrs, initMins, initSecs) • { • zone = initZone; • } • The base class’ constructor is called before the derived • class’ constructor code is executed

  26. Constructors and Destructors in Derived Classes (continued) • Destruction takes place in the opposite order of construction • Therefore, the derived class’ destructor is invoked before • the base class’ destructor

  27. Constructor/Destructor Example class Point { // From “C++: How to Program, by Dietel & Dietel public: Point(int = 0, int = 0); ~Point(); protected: int x, y; {; class Circle: public Point { public: Circle(double r = 0.0, int x = 0, int y = 0); ~Circle(); private: double radius; };

  28. Constructor/Destructor Example (continued) Point::Point(int a, int b) { x = a; y = b; cout << “Point constructor: “ << ‘[‘ << x << “, “ << y << ‘]’ << endl; } Point::~Point() { cout << “Point destructor: “ << ‘[‘ << x << “, “ << y << ‘]’ << endl; }

  29. Constructor/Destructor Example (continued) Circle::Circle(double r, int a, int b) : Point(a, b) { radius = r; cout << “Circle constructor: radius is “ << radius << “ [“ << x << “, “ << y << ‘]’ << endl; } Circle::~Circle() { cout << “Circle destructor: radius is “ << radius << “ [“ << x << “, “ << y << ‘]’ << endl; }

  30. Constructor/Destructor Example (continued) #include <iostream.h> #include “point.h” #include “circle.h” void main() { { Point p(11, 22); } cout << endl; Circle circle1(4.5, 72, 29); cout << endl; Circle circle2(10.0, 5, 5); cout << endl; }

  31. Constructor/Destructor Example (continued) Point constructor: [11, 22] Point destructor: [11, 22] Point constructor: [72, 29] Circle constructor: radius is 4.5 [72, 29] Point constructor: [5, 5] Circle constructor: radius is 10.0 [5, 5] Circle destructor: radius is 10.0 [5, 5] Point destructor: [5, 5] Circle destructor: radius is 4.5 [72, 29] Point destructor: [72, 29]

  32. Multiple Inheritance

More Related