Object
Object-
-Oriented Programming
Oriented Programming
(OOP)
(OOP)
Lecture No. 29
Lecture No. 29
Abstract Class
Abstract Class
Shape
Line Circle Triangle
draw
calcArea
draw
calcArea
draw
calcArea
draw
calcArea
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Understanding Abstract Classes, Virtual Functions, and Destructors in OOP, Slides of Object Oriented Programming
An in-depth exploration of object-oriented programming (oop) concepts, focusing on abstract classes, pure virtual functions, and virtual destructors in c++. Learn how abstract classes implement abstract concepts, cannot be instantiated, and are used for inheriting interfaces and/or implementation. Discover the role of pure virtual functions in making a class abstract and the difference between abstract and concrete classes. Additionally, explore the concept of virtual destructors and their impact on base class destructors when delete operator is applied to a base class pointer.
Typology: Slides
2011/2012
1 / 17
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Object
Object
Oriented Programming
Oriented Programming
(OOP)
(OOP)
Lecture No. 29
Lecture No. 29
Abstract Class
Abstract Class
►
►
Implements an abstract concept
Implements an abstract concept
►
►
Cannot be instantiated
Cannot be instantiated
► ►
Used for inheriting interface and/or
Used for inheriting interface and/or
implementation
implementation
Pure Virtual Functions
Pure Virtual Functions
►
►
A class having pure virtual function(s)
A class having pure virtual function(s)
becomes abstract
becomes abstract
class Shape {
class Shape {
…
…
public:public:
virtual void draw() = 0;
virtual void draw() = 0;
…
…
Shape s;Shape s; // Error!// Error!
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Shape Hierarchy
Shape Hierarchy
Shape
Line Circle Quadrilateral
draw = 0
draw draw
Rectangle
Virtual Destructors
Virtual Destructors
class Quadrilateral : public Shape { class Quadrilateral : public Shape {
public: public:
~Quadrilateral() {
~Quadrilateral() {
cout <<
cout << “
Quadrilateral destructor
Quadrilateral destructor
called
*called *
\
n
n ”
Virtual Destructors
Virtual Destructors
►
►
When delete operator is applied to a base
When delete operator is applied to a base
class pointer, base class destructor is called
class pointer, base class destructor is called
regardless of the object type
regardless of the object type
Virtual Destructors
Virtual Destructors
class Quadrilateral : public Shape { class Quadrilateral : public Shape {
public: public:
virtual ~Quadrilateral() {
virtual ~Quadrilateral() {
cout <<
cout << “
Quadrilateral destructor
Quadrilateral destructor
called
*called *
\
n
n ”
Virtual Destructors
Virtual Destructors
►
►
Now base class destructor will run after the
Now base class destructor will run after the
derived class destructor
derived class destructor
Inherit interface and
Inherit interface and
implementation
implementation
Shape
Line Circle Triangle
draw = 0
calcArea
draw draw
calcArea
draw
calcArea
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Inherit interface and
Inherit interface and
implementation
implementation
►
►
Each derived class of
Each derived class of
Shape
Shape
inherits default
inherits default
implementation of implementation of calcArea()calcArea()
► ► Some may override this, such asSome may override this, such as CircleCircle
and and TriangleTriangle
► ► Others may not, such asOthers may not, such as PointPoint andand LineLine
Example
Example
V Table
V Table
calcArea
draw
Shape vTable
… draw
Line vTable
calcArea
Line object
Shape …
point1 = p
point2 = p
Conclusion
Conclusion
► ► Polymorphism addsPolymorphism adds
Memory overhead due to vTables
Memory overhead due to vTables
Processing overhead due to extra pointerProcessing overhead due to extra pointer
manipulation
manipulation
► ► However, this overhead is acceptable forHowever, this overhead is acceptable for
many of the applications
many of the applications
►
►