Advanced C Topics Chapter 8 CS 308 Chapter

Advanced C++ Topics Chapter 8 CS 308 Chapter 8 -- Advanced C++ Topics

n This chapter describes techniques that make collections of reusable software components possible. Inheritance n Virtual Functions and Late Bindings n Friends n Class Templates n Overloaded Operators n Iterators n CS 308 Chapter 8 -- Advanced C++ Topics 2

Inheritance Revisited n Inheritance is a relationship among classes. One class can derive the behavior and structure of another class. n On the next page we see relationships among timepieces n CS 308 Chapter 8 -- Advanced C++ Topics 3

n CS 308 A digital alarm clock is a digital clock Chapter 8 -- Advanced C++ Topics 4

Def: derived class (subclass) n Def: base class (superclass) n n In C++, a derived class inherits all the members of its base class, excepts the constructors and destructor. n Some languages allow you to have more than 1 base class. CS 308 Chapter 8 -- Advanced C++ Topics 5

n CS 308 Inheritance allows you to reuse software components when you define a new class. Chapter 8 -- Advanced C++ Topics 6

Class Sphere{ public: Sphere(); Sphere(double initial. Radius); void Set. Radius(double new. Radius); double get. Radius() const; double get. Diameter() cosnt; double get. Circumference(); double get. Area() const; double get. Volume() const; double display. Statistics() const; private: double the. Radius; }; CS 308 Chapter 8 -- Advanced C++ Topics 7

Class Ball: public Sphere { public: Ball(); Ball(double initial. Radius, cosnt string initial. Name); void get. Name(string current. Name) const; void set. Name(const string new. Name); void reset. Ball(double new. Radius, const string new. Name); double display. Statistics() const; private: string the. Name; }; CS 308 Chapter 8 -- Advanced C++ Topics 8

Ball: : Ball() : Sphere() { set. Name(“”); } Ball: : Ball(double initial. Radius, const string initial. Name): Sphere(initial. Radius) { set. Name(initial. Name); } void Ball: : reset. Ball(double new. Radius, const string new. Name) { set. Radius(new. Radius); set. Name(new. Name); } void Ball: : display. Statistics() const { cout << “statistics for a “<< the. Name << “: ”; Sphere: : display. Statistics(); } CS 308 Chapter 8 -- Advanced C++ Topics 9

n n n Ball my. Ball(5. 0, “Volleyball”); Sphere my. Shpere(); The compiler can tell which function to use at compile time and this is called early binding or static binding CS 308 Chapter 8 -- Advanced C++ Topics 10

n A derived class’s constructor executes after the base class’s constructor. n n Built inside out The destructor of the derived class executes before the destructor of the base class. n CS 308 Destroyed outside in Chapter 8 -- Advanced C++ Topics 11

n Addition of the protected section CS 308 Chapter 8 -- Advanced C++ Topics 12

n Public, Private, and Protected Inheritance n Several kinds of inheritance are possible. n The key is -- if you have layers of inheritance, how are the lower layers treated. n Public inheritance n Public and protected members of the base class remain public and protected members of the derived class n Protected inheritance n Public and protected members of the base class are protected members of the derived class n Private inheritance n CS 308 Public and protected members of the base class are private members of the derived class. Chapter 8 -- Advanced C++ Topics 13

n Is-a, Has-a, and As-a Relationships n Is-a relationships - public inheritance n A Ball is a Sphere n Whatever is true of type sphere is also true of type ball n This is called object type compatibility n void display. Diameter(Sphere thing) { cout << “The diameter is “ << thing. get. Diameter() << “. n”; } n n CS 308 Chapter 8 -- Advanced C++ Topics 14

n If you define my. Sphere and my. Ball as n Sphere my. Sphere(2. 0); n Ball my. Ball(5. 0, “Volleyball”); n The following calls are legal: n display. Diameter(my. Sphere); n display. Diameter(my. Ball); CS 308 Chapter 8 -- Advanced C++ Topics 15

n Has-a relationship n A ball point pen has a ball n class Pen {. . . Private: Ball point; }; n n n CS 308 Thus another name for the has-a relationship is containment. Chapter 8 -- Advanced C++ Topics 16

n As-a relationship n You can implement a Stack as a list n class Stack: private List n Thus within the Stack you can manipulate the list by using list’s methods. n Both descendants and clients of stack, however, would not be able to access any members of List. CS 308 Chapter 8 -- Advanced C++ Topics 17

Virtual Functions and Late Binding n Example: n Case 1: n Sphere *sphere. Ptr = &my. Sphere n sphere. Ptr->display. Statistics(); n Case 2: n sphere. Ptr = &my. Ball; n sphere. Ptr->display. Statistics(); n CS 308 What is the difference, what functions get called? Chapter 8 -- Advanced C++ Topics 18

n Answer: They both invoke sphere’s version of display. Statistics() because of early binding. n We need to tell the compiler that the function might be changed so it will not bind at compile time but will wait until run-time to see which one to call. n You do this with the keyword virtual CS 308 Chapter 8 -- Advanced C++ Topics 19

n In the base class you do it this way n class n n Sphere{ public: . . . virtual void display. Statistics() const; . . . n }; n CS 308 Now the compiler will do late binding or dynamic binding. Chapter 8 -- Advanced C++ Topics 20

n display. Statistics is called a polymorphic function n polymorphism means many forms. n We also say that Balls’ version of display. Statistics overrides Sphere’s version n Now let’s look at some examples of how early and late binding can interact. CS 308 Chapter 8 -- Advanced C++ Topics 21

n Assume display statistics is virtual and get. Area is not. n Now if it is. . CS 308 Chapter 8 -- Advanced C++ Topics 22

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n Abstract Base Classes n If your base class has a virtual function that all of its descendants will have to overload, n you can give just a prototype and no code n This is called a pure virtual function n virtual void set. Radius(double new. Radius) = 0; n Any class with pure virtual functions (or a derived class that has not defined all pure virtual functions) is called an Abstract Base class, and no instances of it can be declared. CS 308 Chapter 8 -- Advanced C++ Topics 25

Friends n Declaring a non-member function as a friend to a class allows that function to access all the private members of the class n For example: input and output functions are often defined as friend functions n You also saw class fiends in your linked list nodes. CS 308 Chapter 8 -- Advanced C++ Topics 26

Class Templates You can avoid multiple class definitions by using a C++ class template to specify a class in terms of a data-type parameter. n You have used templates since the middle of CS 202 n CS 308 Chapter 8 -- Advanced C++ Topics 27

Overloaded Operators An operator with more than one meaning is said to be overloaded and is an example of a simple form of polymorphism n To overload an operator, you define an operator function whose name has the form n n n operator symbol where symbol is the operator that you want to overload CS 308 Chapter 8 -- Advanced C++ Topics 28

Iterators An iterator traverses a collection of objects n Typically an iterator has an operation that accesses the item it currently references. n n n Usually this is implemented by overloading the dereference operator, * Iterators also have operations that move the iterator forward and backward through a collection (++, --). They also usually have == and != overloaded as well. CS 308 Chapter 8 -- Advanced C++ Topics 29

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