Lecturespecial

Lecturespecial

• 1.
  Inheritance In C++  Inheritanceis a mechanism for • building class types from other class types • defining new class types to be a –specialization –augmentation of existing types
• 2.
  Inheritance Subgroupings with respectto a parent are called – Subclass – Derived Class – Children The derived class – inherits from the parent all • characteristics • properties • capabilities – can modify or extend inherited abilities
• 3.
  Inheritance VEHICLE LANDBASED AUTOMOBILE BICYCLE • Considerthe vehicle hierarchy: • Note that each entity is also a class • Classes are used in an object centered paradigm as a means of encapsulating common data and functions shared by members of the class
• 4.
  Class and InstanceHierarchy We actually have two hierarchies AUTOMOBILE BICYCLE LANDBASED VEHICLE myAutomyBicycle myLandBased myVehicle
• 5.
  Single/Multiple Inheritance Single Inheritance Eachclass or instance object has a single parent Multiple Inheritance Classes inherit from multiple base classes ( might not have same ancestors as shown in the example below) Defines a relationship Between several (independent) class types Vehicle LandBased WaterBased Automobile MotorBoat AutoBoat Example: Multiple Parents Common Ancestor
• 6.
  Virtual Inheritance The derivedclass AutoBoat… Inherits Attributes and Properties From Automobile MotorBoat Vehicle Vehicle LandBased WaterBased Automobile MotorBoat AutoBoat
• 7.
  Derivation Hierarchy • Theclass Vehicle is an abstraction… – It represents an encapsulation of common • Properties • Attributes • Its sole purpose – Define a class from which to derive other classes…. • It encapsulates common – Data members – Function members • Called – Abstract Base Class – Abstract Super Class
• 8.
  Class Derivation Any classcan serve as a base class… – Thus a derived class can also be a base class – Worth spending time at the outset of a design to develop sound definitions syntax class DerivedClassName:specification BaseClassName DerivedClassName - the class being derived specification - specifies access to the base class members public protected private - private by default
• 9.
  Class Derivation Class Cbe derived from base class A - PUBLIC class C : public A In class C The inherited public members of A Appear as public members of C If myValue is a public data member of A myValue can be accessed publicly through instances of C C myC; myC.myValue; // ok
• 10.
  Class Derivation Class Cbe derived from base class B - PRIVATE class C : private B In class C The inherited public members of B Appear as private members of C if myValue is a public data member of B myValue cannot be accessed publicly and directly through instances of C C myC; myC.myValue; // compile error Function members of C can still access public members of B as public
• 11.
  Simple Inheritance -Example #include <iostream> class BaseClass { public: BaseClass( ) : baseValue (20) { }; BaseClass(int aValue) : baseValue (aValue) { }; int baseValue; }; class DerivedClass : public BaseClass { public: DerivedClass() : derivedValue (10){ }; DerivedClass(int aDerivedValue) : BaseClass(15), derivedValue(aDerivedValue){ }; int getDerivedValue() { return derivedValue; } private: int derivedValue; }; int main( ) { BaseClass base; DerivedClass child(5); cout << base.baseValue << endl; // will print 20 cout << child.baseValue << endl; // will print 15 cout << child.getDerivedValue() << endl; // will print 5 return 0; }
• 12.
  Derived Class –Public Inheritance • Generally all data is private, so we just add additional data members in the derived class by specifying them in the private section • Any base class member functions that are not specified in the derived class are inherited unchanged, with the following exceptions: constructor, destructor, copy constructor, and operator=. • Any base class member function that is declared in the derived class’ private section is disabled in the derived class • Any base class member function that is declared in the derived class’ public section requires an overriding definition that will be applied to objects of the derived class • Additional member functions can be added in the derived class
• 13.
  Derived Class-Public Inheritance classDerived : public Base { // Any members that are not listed are inherited unchanged except // for constructor, destructor, copy constructor, and operator= public: // Constructors, and destructors if defaults are not good // Base members whose definitions are to change in Derived // Additional public member functions private: // Additional data members (generally private) // Additional private member functions // Base members that should be disabled in Derived };
• 14.
  Visibility rules • Anyprivate members in the base class are not accessible to the derived class (because any member that is declared with private visibility is accessible only to methods of the class) • What if we want the derived class to have access to the base class members? 1) use public access =>public access allows access to other classes in addition to derived classes 2) use a friend declaration=>this is also poor design and would require friend declaration for each derived class 3) make members protected =>allows access only to derived classes A protected class member is private to every class except a derived class, but declaring data members as protected or public violates the spirit of encapsulation 1) write accessor and modifier methods =>the best alternative Note: However, if a protected declaration allows you to avoid convoluted code, then it is not unreasonable to use it.
• 15.
  Class Derivation Constructors andDestructors • Constructors and destructors are not inherited – Each derived class should define its constructors/destructor – If no constructor is written=> hidden constructor is generated and will call the base default constructor for the inherited portion and then apply the default initialization for any additional data members • When a derived object is instantiated, memory is allocated for – Base object – Added parts • Initialization occurs in two stages: – the base class constructors are invoked to initialize the base objects – the derived class constructor is used to complete the task • The derived class constructor specifies appropriate base class constructor in the initialization list – If there is no constructor in base class, the compiler created default constructor used • If the base class is derived, the procedure is applied recursively
• 16.
  Inherited Member Initialization •Initialized in two ways: – If the base class has only a default constructor=> initialize the member values in the body of the derived class constructor – If the base class has a constructor with arguments=> the initialization list is used to pass arguments to the base class constructors syntax (for Single Base Class) DerivedClass ( derivedClass args ) : BaseClass ( baseClass args ) { DerivedClass constructor body } • The set of derived class constructor arguments may contain initialization values for the base class arguments
• 17.
  Derived class DateTime classDateTime : public Date // derived from base class Date { private: // additional data members int hour, minutes; public: // additional member functions void DateTime(); //default constructor void DateTime(const char* mm_dd_yy, int h, int mi); // constructor void setTime(int h, int m); void addMinutes(int m); void addHours(int h); void display(void) const; // overrides Date::display() };
• 18.
  Derived Class DateTime DateTime::DateTime(constchar * mm_dd_yy, int h, int mi) : Date(mm_dd_yy) , hours(h) , minutes(mi) // invokes the constructor Date(const char* mmddyy) {} void DateTime::display() const { //add the code for displaying the date and time . //Hint : cout<<(Date&)(*this)<<endl; will display the date } void DateTime::AddHours(int h) { //make sure that if the hours goes more than 24 you have to add 1 day // and you can do that as follows (*this) += 1; }
• 19.
  Derived Class DateTime intmain(){ DateTime dt(”11/06/01”,20,15); //constructor dt+=5; // operator+=() of class Date cout << ”Date is: ” << justdt<<endl; dt.AddHours(2); // AddHours() of class DateTime dt.display(); // display() of class DateTime return 0; }