C++面向对象程序设计第七章

C++面向对象程序设计

13Object-Oriented Programming: Polymorphism

C++面向对象程序设计

OBJECTIVESIn this chapter you will learn: What polymorphism is, how it makes programming more convenient, and how it makes systems more extensible and maintainable. To declare and use virtual functions to effect polymorphism. The distinction between abstract and concrete classes. To declare pure virtual functions to create abstract classes. How to use run-time type information (RTTI) with downcasting, dynamic_cast, typeid and type_info. How C++ implements virtual functions and dynamic binding "under the hood." How to use virtual destructors to ensure that all appropriate destructors run on an object.

C++面向对象程序设计

13.1 13.2 13.3

Introduction Polymorphism Examples Relationships Among Objects in an Inheritance Hierarchy 13.3.1 13.3.2 13.3.3 13.3.4 13.3.5 Invoking Base-Class Functions from DerivedClass Objects Aiming Derived-Class Pointers at Base-Class Objects Derived-Class Member-Function Calls via BaseClass Pointers Virtual Functions Summary of the Allowed Assignments Between Base-Class and Derived-Class Objects and Pointers

13.4 13.5

Type Fields and switch Statements Abstract Classes and Pure virtual Functions

C++面向对象程序设计

13.6

Case Study: Payroll System Using Polymorphism 13.6.1 13.6.2 13.6.3 13.6.4 13.6.5 13.6.6 Creating Abstract Base Class Employee Creating Concrete Derived Class SalariedEmployee Creating Concrete Derived Class HourlyEmployee Creating Concrete Derived Class CommissionEmployee Creating Indirect Concrete Derived ClassBasePlusCommissionEmployee

Demonstrating Polymorphic Processing

13.7 13.8

(Optional) Polymorphism, Virtual Functions and Dynamic Binding "Under the Hood" Case Study: Payroll System Using Polymorphism and Run-Time Type Information with Downcasting, dynamic_cast, typeid andtype_info

13.9 13.10 13.11

Virtual Destructors (Optional) Software Engineering Case Study: Incorporating Inheritance into the ATM System Wrap-Up

C++面向对象程序设计

Software Engineering Observation 13.1With virtual functions and polymorphism, you can deal in generalities and let the execution-time environment concern itself with the specifics. You can direct a variety of objects to behave in manners appropriate to those objects without even knowing their types (as long as those objects belong to the same inheritance hierarchy and are being accessed off a common base-class pointer).

C++面向对象程序设计

Software Engineering Observation 13.2Polymorphism promotes extensibility: Software written to invoke polymorphic behavior is written independently of the types of the objects to which messages are sent. Thus, new types of objects that can respond to existing messages can be incorporated into such a system without modifying the base system. Only client code that instantiates new objects must be modified to accommodate new types.

C++面向对象程序设计

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// Fig. 13.1: CommissionEmployee.h // CommissionEmployee class definition represents a commission employee. #ifndef COMMISSION_H #define COMMISSION_H #include <string> // C++ standard string class using s

td::string; class class CommissionEmployee

Outline

Commission Employee.h

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10 { 11 public: public: 12 13 14 15 16 17 18 19 20 21 22 23 24 25 void setGrossSales( double ); // set gross sales amount const; double getGrossSales() const; // return gross sales amount void setSocialSecurityNumber( const string & ); // set SSN getSocialSecurityNumber() const; string getSocialSecurityNumber() const; // return SSN void setLastName( const string & ); // set last name const; string getLastName() const; // return last name void setFirstName( const string & ); // set first name getFirstName() const; string getFirstName() const; // return first name CommissionEmployee( const string &, const string &, const string &, 0.0, double = 0.0, double = 0.0 );

C++面向对象程序设计

26 27 28 29 30 31 33 34 35 36 37 39 40 #endif const; double earnings() const; // calculate earnings const; object void print() const; // print CommissionEmployee object string firstName; string lastName; string socialSecurityNumber; double grossSales; // gross weekly sales double commissionRate; // commission percentage void setCommissionRate( double ); // set commission rate const; double getCommissionRate() const; // return commission rate

Outline

32 private: private:

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38 }; // end class CommissionEmployee

C++面向对象程序设计

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// Fig. 13.2: CommissionEmployee.cpp member// Class CommissionEmployee member-function definitions. #include <iostream> using std::cout; #include "CommissionEmployee.h" // CommissionEmployee class definition

Outline

// constructor 9 CommissionEmployee::CommissionEmployee( CommissionEmployee::CommissionEmployee( 10 const string &first, const string &last, const string &ssn, 11 double sales, double rate ) 12 : firstName( first ), lastName( last ), socialSecurityNumber( ssn ) 13 { 14 setGrossSales( sales ); // validate and store gross sales 15 setCommissionRate( rate ); // validate and store commission rate 16 } // end CommissionEmployee constructor 17 18 19 20 21 22 23 24 25 26 27 28 // set first name void CommissionEmployee::setFirstName( const string &first ) { firstName = first; // should validate } // end function setFirstName // return first name string CommissionEmployee::getFirstName() const { return firstName; } // end function getFirstName

Commission Employee.cpp

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C++面向对象程序设计

29 30 // set last name 31 void CommissionEmployee::setLastName( const string &last ) 32 { lastNa …… 此处隐藏：5441字，全部文档内容请下载后查看。喜欢就下载吧 ……