Object Oriented Programming Using C CLASS 12 1 Objectives Using inheritance to promote software reusability 2 What is Inheritance Inheritance allows a new class to be based on an existing class The new class inherits the protected member variables and public functions of the class it is based on Represents an is a relationship 3 hardware cpp models hardware store inventory using inheritance include iostream h const int LEN 80 class items private char name LEN item name float price item price int quantity number in stock 4 public void getdata get data from user cout n Enter item name cin name cout Enter price format 12 95 cin price cout Enter quantity in stock cin quantity void putdata display data cout n Name name cout n Price price cout nQuantity quantity 5 class pipe public item pipe class private float length length of pipe float size size of pipe char type LEN type of pipe public void getdata get data from user item getdata cout Enter length cin length cout Enter size cin size cout Enter type cin type 6 void putdata display data item putdata cout n Length length cout n Size size cout n Type type 7 class light bulbs public item private int watts wattage of light bulbs public void getdata get data from user item getdata cout Enter wattage cin watts void putdata display data item putdata cout n Wattage watts 8 class tools public item tool class no additional data 9 class paint public item paint class private int size size of pints char color LEN color of paint public void getdata getdata from user item getdata cout Enter size pints cin size cout Enter color cin color void putdata display data item putdata cout n Size size cout n Color color 10 void main pipe p1 make one item lightbulbs b1 of each class tools t1 paint pnt1 cout endl cout nEnter data for pipe item p1 getdata cout nEnter data for light bulb item b1 getdata p1 putdata b1 putdata 11 void main pipe p1 make one item lightbulbs b1 of each class tools t1 paint pnt1 cout endl cout nEnter data for pipe item p1 getdata cout nEnter data for light bulb item b1 getdata p1 putdata b1 putdata 12 Constructors and Destructors in Inheritance Constructor Order Constructor of any objects within the Base Class Constructor of the base class Constructor of objects within the Derived class Constructor of the Derived class Destructor is the reverse 13 Points to Remember Software Engineering Observations 14 Software Engineering Observations A derived class cannot directly access private members of its base class 15 Software Engineering Observations Suppose we create an object of a derived class where both the base class and the derived class contain objects of other classes When an object of that derived class is created first the constructors for the base class member objects execute then the base class constructor executes then the constructors for the derived class member objects execute then the derived class constructor executes Destructors are called in the reverse of the order in which their corresponding constructors are called 16 Software Engineering Observations The order in which member objects are constructed is the order in which those objects are declared within the class definition The order in which the member initializers are listed does not affect construction 17 Software Engineering Observations In inheritance base class constructors are called in the order in which inheritance is specified in the derived class definition The order in which the base class constructors are specified in the derived class member initializer list does not affect the order of construction 18 Software Engineering Observations Creating a derived class does not affect it s base class s source code or object code the integrity of a base class is preserved by inheritance 19 Software Engineering Observations In an object oriented system classes are often closely related Factor out common attributes and behavior and place these in a base class Then use inheritance to form derived classes 20 Software Engineering Observations A derived class contains the attributes and behaviors of its base class A derived class can also contain additional attributes and behaviors With inheritance the base class can be compiled independent of the derived class Only the derived class s incremental attributes and behaviors need to be compiled to be able to combine these with the base class to form a derived class 21 Software Engineering Observations Modifications to a base class do not require derived classes to change as long as the public and protected interfaces to the base class remain unchanged Derived classes may however need to be recompiled 22 Software Engineering Observations Program modifications to a class that is a member of another class do not require the enclosing class to change as long as the public interface to the member class remains unchanged Note that the composite class may however need to be recompiled 23 Looking at Some Examples 24 class Employee public Employee const char const char void print const Employee private char firstName char lastName 25 Employee Employee const char first const char last firstName new char strlen first 1 assert firstName 0 strcpy firstNmae first lastName new char strlen last 1 assert lastName last Employee print cout firstName lastName Employee Employee delete first Name delete lastName 26 class HourlyWorker public Employee public HourlyWorker const char const char double double double getPay const void print const private double wage double hours 27 HourlyWorker HourlyWorker const char first const char last double initHours double initWage Employee first last hours initHours wage initWage double HourlyWorker getPay const return wage hours void HourlyWorker print const Employee print cout is an hourly worker with pay of getPay 28 int main HourlyWorker h Bob Smith 40 0 10 00 h print return 0 29 Object Oriented Design Employee database of salaried managers permanent hourly employees temporary hourly employees 30 In Class Exercise Getting Up to Speed with Inheritance Create an inheritance scheme a UML diagram and the interfaces for the following 31 Getting Up to Speed with Inheritance Salaried Hrly Perm name name home phone home phone office phone office phone salary level wage bonus level reports to reports to assistant Hrly Temp name home phone office phone wage reports to 32 class employee public employee char name char home phone char office phone reports to void show employee void private char name 64 char home