Nheritance, polymorphism, and virtual functions

Сентябрь 7, 2022

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Nheritance, polymorphism, and virtual functions

Содержание

2. What Is Inheritance? Provides a way to create a new class from an existing class The
3. Example: Insect Taxonomy CS1 -- Inheritance and Polymorphism
4. The "is a" Relationship Inheritance establishes an "is a" relationship between classes. A poodle is a
5. Inheritance – Terminology and Notation in C++ Base class (or parent) – inherited from Derived class
6. Back to the ‘is a’ Relationship An object of a derived class 'is a(n)' object of
7. What Does a Child Have? An object of the derived class has: all members defined in
8. Protected Members and Class Access protected member access specification: like private, but accessible by objects of
9. Class Access Specifiers public – object of derived class can be treated as object of base
10. Inheritance vs. Access CS1 -- Inheritance and Polymorphism
11. Inheritance vs. Access CS1 -- Inheritance and Polymorphism
12. Inheritance vs. Access CS1 -- Inheritance and Polymorphism
13. Inheritance vs. Access CS1 -- Inheritance and Polymorphism
14. Constructors and Destructors in Base and Derived Classes Derived classes can have their own constructors and
15. Constructors and Destructors in Base and Derived Classes CS1 -- Inheritance and Polymorphism
16. Constructors and Destructors in Base and Derived Classes CS1 -- Inheritance and Polymorphism
17. Constructors and Destructors in Base and Derived Classes CS1 -- Inheritance and Polymorphism
18. Passing Arguments to Base Class Constructor Allows selection between multiple base class constructors Specify arguments to
19. Passing Arguments to Base Class Constructor CS1 -- Inheritance and Polymorphism Square::Square(int side):Rectangle(side,side) derived class constructor
20. Redefining Base Class Functions Redefining function: function in a derived class that has the same name
21. Redefining Base Class Functions Not the same as overloading – with overloading, parameter lists must be
22. Base Class CS1 -- Inheritance and Polymorphism
23. Derived Class CS1 -- Inheritance and Polymorphism Redefined setScore function
24. Driver Program CS1 -- Inheritance and Polymorphism
25. Problem with Redefining Consider this situation: Class BaseClass defines functions x() and y(). x() calls y().
26. Problem with Redefining CS1 -- Inheritance and Polymorphism BaseClass DerivedClass void X(); void Y(); void Y();
27. Class Hierarchies CS1 -- Inheritance and Polymorphism A base class can be derived from another base
28. Class Hierarchies CS1 -- Inheritance and Polymorphism Consider the GradedActivity, FinalExam, PassFailActivity, PassFailExam hierarchy in Chapter
29. Polymorphism and Virtual Member Functions Virtual member function: function in base class that expects to be
30. Polymorphism and Virtual Member Functions CS1 -- Inheritance and Polymorphism Because the parameter in the displayGrade
31. CS1 -- Inheritance and Polymorphism
32. CS1 -- Inheritance and Polymorphism As you can see from the example output, the getLetterGrade member
33. Static Binding Program 15-10 displays 'C' instead of 'P' because the call to the getLetterGrade function
34. Virtual Functions A virtual function is dynamically bound to calls at runtime. At runtime, C++ determines
35. Virtual Functions To make a function virtual, place the virtual key word before the return type
36. Updated Version of GradedActivity CS1 -- Inheritance and Polymorphism The function is now virtual. The function
37. Polymorphism CS1 -- Inheritance and Polymorphism If we recompile our program with the updated versions of
38. CS1 -- Inheritance and Polymorphism
39. CS1 -- Inheritance and Polymorphism
40. Polymorphism Requires References or Pointers Polymorphic behavior is only possible when an object is referenced by
41. Base Class Pointers CS1 -- Inheritance and Polymorphism Can define a pointer to a base class
42. Base Class Pointers Base class pointers and references only know about members of the base class
43. Redefining vs. Overriding In C++, redefined functions are statically bound and overridden functions are dynamically bound.
44. Virtual Destructors It's a good idea to make destructors virtual if the class could ever become
45. Abstract Base Classes and Pure Virtual Functions Pure virtual function: a virtual member function that must
46. Abstract Base Classes and Pure Virtual Functions Abstract base class: class that can have no objects.
47. Multiple Inheritance CS1 -- Inheritance and Polymorphism A derived class can have more than one base
49. Скачать презентацию

Слайд 2

What Is Inheritance?
Provides a way to create a new class from

an existing class
The new class is a specialized version of the existing class

CS1 -- Inheritance and Polymorphism

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Example: Insect Taxonomy
CS1 -- Inheritance and Polymorphism

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The "is a" Relationship
Inheritance establishes an "is a" relationship between classes.
A

poodle is a dog
A car is a vehicle
A flower is a plant
A football player is an athlete

CS1 -- Inheritance and Polymorphism

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Inheritance – Terminology and Notation in C++
Base class (or parent) –

inherited from
Derived class (or child) – inherits from the base class
Notation:
class Student // base class
{
. . .
};
class UnderGrad : public student
{ // derived class
. . .
};

CS1 -- Inheritance and Polymorphism

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Back to the ‘is a’ Relationship
An object of a derived class

'is a(n)' object of the base class
Example:
an UnderGrad is a Student
a Mammal is an Animal
A derived object has all of the characteristics of the base class

CS1 -- Inheritance and Polymorphism

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What Does a Child Have?
An object of the derived class has:
all

members defined in child class
all members declared in parent class
An object of the derived class can use:
all public members defined in child class
all public members defined in parent class

CS1 -- Inheritance and Polymorphism

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Protected Members and Class Access
protected member access specification: like private, but

accessible by objects of derived class
Class access specification: determines how private, protected, and public members of base class are inherited by the derived class

CS1 -- Inheritance and Polymorphism

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Class Access Specifiers
public – object of derived class can be treated

as object of base class (not vice-versa)
protected – more restrictive than public, but allows derived classes to know details of parents
private – prevents objects of derived class from being treated as objects of base class.

CS1 -- Inheritance and Polymorphism

Слайд 10

Inheritance vs. Access
CS1 -- Inheritance and Polymorphism

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Inheritance vs. Access
CS1 -- Inheritance and Polymorphism

Слайд 12

Inheritance vs. Access
CS1 -- Inheritance and Polymorphism

Слайд 13

Inheritance vs. Access
CS1 -- Inheritance and Polymorphism

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Constructors and Destructors in Base and Derived Classes
Derived classes can have

their own constructors and destructors
When an object of a derived class is created, the base class’s constructor is executed first, followed by the derived class’s constructor
When an object of a derived class is destroyed, its destructor is called first, then that of the base class

CS1 -- Inheritance and Polymorphism

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Constructors and Destructors in Base and Derived Classes
CS1 -- Inheritance and

Polymorphism

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Constructors and Destructors in Base and Derived Classes
CS1 -- Inheritance and

Polymorphism

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Constructors and Destructors in Base and Derived Classes
CS1 -- Inheritance and

Polymorphism

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Passing Arguments to Base Class Constructor
Allows selection between multiple base class

constructors
Specify arguments to base constructor on derived constructor heading:
Square::Square(int side) : Rectangle(side, side)
Can also be done with inline constructors
Must be done if base class has no default constructor

CS1 -- Inheritance and Polymorphism

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Passing Arguments to Base Class Constructor
CS1 -- Inheritance and Polymorphism
Square::Square(int side):Rectangle(side,side)
derived

class constructor

base class constructor

derived constructor parameter

base constructor parameters

Слайд 20

Redefining Base Class Functions
Redefining function: function in a derived class that

has the same name and parameter list as a function in the base class
Typically used to replace a function in base class with different actions in derived class

CS1 -- Inheritance and Polymorphism

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Redefining Base Class Functions
Not the same as overloading – with overloading,

parameter lists must be different
Objects of base class use base class version of function; objects of derived class use derived class version of function

CS1 -- Inheritance and Polymorphism

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Base Class
CS1 -- Inheritance and Polymorphism

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Derived Class
CS1 -- Inheritance and Polymorphism
Redefined setScore function

Слайд 24

Driver Program
CS1 -- Inheritance and Polymorphism

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Problem with Redefining
Consider this situation:
Class BaseClass defines functions x() and y().

x() calls y().
Class DerivedClass inherits from BaseClass and redefines function y().
An object D of class DerivedClass is created and function x() is called.
When x() is called, which y() is used, the one defined in BaseClass or the the redefined one in DerivedClass?

CS1 -- Inheritance and Polymorphism

Слайд 26

Problem with Redefining
CS1 -- Inheritance and Polymorphism
BaseClass
DerivedClass
void X();
void Y();
void Y();
DerivedClass D;
D.X();
Object

D invokes function X()
In BaseClass. Function X()
invokes function Y() in BaseClass, not function Y() in DerivedClass,
because function calls are bound at compile time. This is static binding.

Слайд 27

Class Hierarchies
CS1 -- Inheritance and Polymorphism
A base class can be derived

from another base class.

Слайд 28

Class Hierarchies
CS1 -- Inheritance and Polymorphism
Consider the GradedActivity, FinalExam, PassFailActivity, PassFailExam

hierarchy in Chapter 15.

Слайд 29

Polymorphism and Virtual Member Functions
Virtual member function: function in base class

that expects to be redefined in derived class
Function defined with key word virtual:
virtual void Y() {...}
Supports dynamic binding: functions bound at run time to function that they call
Without virtual member functions, C++ uses static (compile time) binding

CS1 -- Inheritance and Polymorphism

Слайд 30

Polymorphism and Virtual Member Functions
CS1 -- Inheritance and Polymorphism
Because the parameter

in the displayGrade function is a GradedActivity reference variable, it can reference any object that is derived from GradedActivity. That means we can pass a GradedActivity object, a FinalExam object, a PassFailExam object, or any other object that is derived from GradedActivity.
A problem occurs in Program 15-10 however...

Слайд 31

CS1 -- Inheritance and Polymorphism

Слайд 32

CS1 -- Inheritance and Polymorphism
As you can see from the example

output, the getLetterGrade member function returned ‘C’ instead of ‘P’. This is because the GradedActivity class’s getLetterGrade function was executed instead of the PassFailActivity class’s version of the function.

Слайд 33

Static Binding
Program 15-10 displays 'C' instead of 'P' because the call

to the getLetterGrade function is statically bound (at compile time) with the GradedActivity class's version of the function. We can remedy this by making the function virtual.

CS1 -- Inheritance and Polymorphism

Слайд 34

Virtual Functions
A virtual function is dynamically bound to calls at runtime. At

runtime, C++ determines the type of object making the call, and binds the function to the appropriate version of the function.

CS1 -- Inheritance and Polymorphism

Слайд 35

Virtual Functions
To make a function virtual, place the virtual key word

before the return type in the base class's declaration:
virtual char getLetterGrade() const;
The compiler will not bind the function to calls. Instead, the program will bind them at runtime.

CS1 -- Inheritance and Polymorphism

Слайд 36

Updated Version of GradedActivity
CS1 -- Inheritance and Polymorphism
The function is now

virtual.

The function also becomes virtual in all derived classes automatically!

Слайд 37

Polymorphism
CS1 -- Inheritance and Polymorphism
If we recompile our program with the

updated versions of the classes, we will get the right output, shown here: (See Program 15-11 in the book.)

This type of behavior is known as polymorphism. The term polymorphism means the ability to take many forms.
Program 15-12 demonstrates polymorphism by passing
objects of the GradedActivity and PassFailExam classes to the displayGrade function.

Слайд 38

CS1 -- Inheritance and Polymorphism

Слайд 39

CS1 -- Inheritance and Polymorphism

Слайд 40

Polymorphism Requires References or Pointers
Polymorphic behavior is only possible when an

object is referenced by a reference variable or a pointer, as demonstrated in the displayGrade function.

CS1 -- Inheritance and Polymorphism

Слайд 41

Base Class Pointers
CS1 -- Inheritance and Polymorphism
Can define a pointer to

a base class object
Can assign it the address of a derived class object

Слайд 42

Base Class Pointers
Base class pointers and references only know about members

of the base class
So, you can’t use a base class pointer to call a derived class function
Redefined functions in derived class will be ignored unless base class declares the function virtual

CS1 -- Inheritance and Polymorphism

Слайд 43

Redefining vs. Overriding
In C++, redefined functions are statically bound and overridden

functions are dynamically bound. So, a virtual function is overridden, and a non-virtual function is redefined.

CS1 -- Inheritance and Polymorphism

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Virtual Destructors
It's a good idea to make destructors virtual if the

class could ever become a base class.
Otherwise, the compiler will perform static binding on the destructor if the class ever is derived from.
See Program 15-14 for an example

CS1 -- Inheritance and Polymorphism

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Abstract Base Classes and Pure Virtual Functions
Pure virtual function: a virtual

member function that must be overridden in a derived class that has objects
Abstract base class contains at least one pure virtual function:
virtual void Y() = 0;
The = 0 indicates a pure virtual function
Must have no function definition in the base class

CS1 -- Inheritance and Polymorphism

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Abstract Base Classes and Pure Virtual Functions
Abstract base class: class that

can have no objects. Serves as a basis for derived classes that may/will have objects
A class becomes an abstract base class when one or more of its member functions is a pure virtual function

CS1 -- Inheritance and Polymorphism

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Multiple Inheritance
CS1 -- Inheritance and Polymorphism
A derived class can have more

than one base class
Each base class can have its own access specification in derived class's definition:
class cube : public square,
public rectSolid;

Nheritance, polymorphism, and virtual functions

Содержание

What Is Inheritance?Provides a way to create a new class from

Example: Insect TaxonomyCS1 -- Inheritance and Polymorphism

The "is a" RelationshipInheritance establishes an "is a" relationship between classes.A

Inheritance – Terminology and Notation in C++Base class (or parent) –

Back to the ‘is a’ RelationshipAn object of a derived class

What Does a Child Have?An object of the derived class has:all

Protected Members and Class Accessprotected member access specification: like private, but

Class Access Specifierspublic – object of derived class can be treated

Inheritance vs. Access CS1 -- Inheritance and Polymorphism

Inheritance vs. AccessCS1 -- Inheritance and Polymorphism

Inheritance vs. AccessCS1 -- Inheritance and Polymorphism

Inheritance vs. AccessCS1 -- Inheritance and Polymorphism

Constructors and Destructors in Base and Derived ClassesDerived classes can have

Constructors and Destructors in Base and Derived ClassesCS1 -- Inheritance and

Constructors and Destructors in Base and Derived ClassesCS1 -- Inheritance and

Constructors and Destructors in Base and Derived ClassesCS1 -- Inheritance and

Passing Arguments to Base Class ConstructorAllows selection between multiple base class

Passing Arguments to Base Class ConstructorCS1 -- Inheritance and PolymorphismSquare::Square(int side):Rectangle(side,side) derived

Redefining Base Class FunctionsRedefining function: function in a derived class that

Redefining Base Class FunctionsNot the same as overloading – with overloading,

Base ClassCS1 -- Inheritance and Polymorphism

Derived Class CS1 -- Inheritance and PolymorphismRedefined setScore function

Driver ProgramCS1 -- Inheritance and Polymorphism

Problem with RedefiningConsider this situation:Class BaseClass defines functions x() and y().

Problem with RedefiningCS1 -- Inheritance and PolymorphismBaseClassDerivedClassvoid X();void Y();void Y();DerivedClass D;D.X();Object

Class HierarchiesCS1 -- Inheritance and PolymorphismA base class can be derived

Class HierarchiesCS1 -- Inheritance and PolymorphismConsider the GradedActivity, FinalExam, PassFailActivity, PassFailExam

Polymorphism and Virtual Member FunctionsVirtual member function: function in base class

Polymorphism and Virtual Member FunctionsCS1 -- Inheritance and PolymorphismBecause the parameter

CS1 -- Inheritance and Polymorphism

CS1 -- Inheritance and PolymorphismAs you can see from the example

Static BindingProgram 15-10 displays 'C' instead of 'P' because the call

Virtual FunctionsA virtual function is dynamically bound to calls at runtime. At

Virtual FunctionsTo make a function virtual, place the virtual key word

Updated Version of GradedActivityCS1 -- Inheritance and PolymorphismThe function is now

PolymorphismCS1 -- Inheritance and PolymorphismIf we recompile our program with the

CS1 -- Inheritance and Polymorphism

CS1 -- Inheritance and Polymorphism

Polymorphism Requires References or PointersPolymorphic behavior is only possible when an

Base Class PointersCS1 -- Inheritance and PolymorphismCan define a pointer to

Base Class PointersBase class pointers and references only know about members

Redefining vs. OverridingIn C++, redefined functions are statically bound and overridden

Virtual DestructorsIt's a good idea to make destructors virtual if the

Abstract Base Classes and Pure Virtual FunctionsPure virtual function: a virtual

Abstract Base Classes and Pure Virtual FunctionsAbstract base class: class that

Multiple InheritanceCS1 -- Inheritance and PolymorphismA derived class can have more

Похожие презентации

What Is Inheritance?
Provides a way to create a new class from

Example: Insect Taxonomy
CS1 -- Inheritance and Polymorphism

The "is a" Relationship
Inheritance establishes an "is a" relationship between classes.
A

Inheritance – Terminology and Notation in C++
Base class (or parent) –

Back to the ‘is a’ Relationship
An object of a derived class

What Does a Child Have?
An object of the derived class has:
all

Protected Members and Class Access
protected member access specification: like private, but

Class Access Specifiers
public – object of derived class can be treated

Inheritance vs. Access
CS1 -- Inheritance and Polymorphism

Inheritance vs. Access
CS1 -- Inheritance and Polymorphism

Inheritance vs. Access
CS1 -- Inheritance and Polymorphism

Inheritance vs. Access
CS1 -- Inheritance and Polymorphism

Constructors and Destructors in Base and Derived Classes
Derived classes can have

Constructors and Destructors in Base and Derived Classes
CS1 -- Inheritance and

Constructors and Destructors in Base and Derived Classes
CS1 -- Inheritance and

Constructors and Destructors in Base and Derived Classes
CS1 -- Inheritance and

Passing Arguments to Base Class Constructor
Allows selection between multiple base class

Passing Arguments to Base Class Constructor
CS1 -- Inheritance and Polymorphism
Square::Square(int side):Rectangle(side,side)
derived

Redefining Base Class Functions
Redefining function: function in a derived class that

Redefining Base Class Functions
Not the same as overloading – with overloading,

Base Class
CS1 -- Inheritance and Polymorphism

Derived Class
CS1 -- Inheritance and Polymorphism
Redefined setScore function

Driver Program
CS1 -- Inheritance and Polymorphism

Problem with Redefining
Consider this situation:
Class BaseClass defines functions x() and y().

Problem with Redefining
CS1 -- Inheritance and Polymorphism
BaseClass
DerivedClass
void X();
void Y();
void Y();
DerivedClass D;
D.X();
Object

Class Hierarchies
CS1 -- Inheritance and Polymorphism
A base class can be derived

Class Hierarchies
CS1 -- Inheritance and Polymorphism
Consider the GradedActivity, FinalExam, PassFailActivity, PassFailExam

Polymorphism and Virtual Member Functions
Virtual member function: function in base class

Polymorphism and Virtual Member Functions
CS1 -- Inheritance and Polymorphism
Because the parameter

CS1 -- Inheritance and Polymorphism
As you can see from the example

Static Binding
Program 15-10 displays 'C' instead of 'P' because the call

Virtual Functions
A virtual function is dynamically bound to calls at runtime. At

Virtual Functions
To make a function virtual, place the virtual key word

Updated Version of GradedActivity
CS1 -- Inheritance and Polymorphism
The function is now

Polymorphism
CS1 -- Inheritance and Polymorphism
If we recompile our program with the

Polymorphism Requires References or Pointers
Polymorphic behavior is only possible when an

Base Class Pointers
CS1 -- Inheritance and Polymorphism
Can define a pointer to

Base Class Pointers
Base class pointers and references only know about members

Redefining vs. Overriding
In C++, redefined functions are statically bound and overridden

Virtual Destructors
It's a good idea to make destructors virtual if the

Abstract Base Classes and Pure Virtual Functions
Pure virtual function: a virtual

Abstract Base Classes and Pure Virtual Functions
Abstract base class: class that

Multiple Inheritance
CS1 -- Inheritance and Polymorphism
A derived class can have more