object oriented programming (oop) - cs304 power point slides lecture 28

8/13/2019 Object Oriented Programming (OOP) - CS304 Power Point Slides Lecture 28

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Object-Oriented Programming(OOP)

Lecture No. 28


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Problem Statement

Develop a function that can draw differenttypes of geometric shapes from an array


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Shape Hierarchy

Shape

Line Circle Triangle

draw

calcArea

drawcalcArea

drawcalcArea

drawcalcArea


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Shape Hierarchy

class Shape {

protected:

char _type; public:Shape() { }void draw(){ cout


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Shape Hierarchy

class Circle : public Shape {

public:

Circle(Point center, double radius){

}

void draw(){ cout


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Shape Hierarchy

class Triangle : public Shape {

public:

Triangle(Line l1, Line l2,double angle)

{ } void draw(){ cout


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Drawing a Scene

int main() {Shape* _shape[ 10 ];Point p1(0, 0), p2(10, 10);

shape[1] = new Line(p1, p2);shape[2] = new Circle(p1, 15);

void drawShapes( shape, 10 );return 0;}


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Function drawShapes()

void drawShapes(Shape* _shape[],int size) {

for (int i = 0; i < size; i++){

_shape[i]->draw();}

}


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Sample Output

ShapeShapeShapeShape


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Function drawShapes()

void drawShapes(Shape* _shape[], int size) {for (int i = 0; i < size; i++) {

// Determine object type with// switch & accordingly call// draw() method

}}


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Required Switch Logicswitch ( _shape[i]->getType() ){

case L : static_cast(_shape[i])->draw();

break;case C :

static_cast(_shape[i])->draw();

break;

}


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Equivalent If Logic

if ( _shape[i]- >getType() == L ) static_cast(_shape[i])->draw();

else if ( _shape[i]- >getType() == C )static_cast(_shape[i])->draw();


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Problems with Switch

Statement


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Delocalized Code

Consider a function that prints area ofeach shape from an input array


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Function printArea

void printArea(Shape* _shape[], int size) {for (int i = 0; i < size; i++) {

// Print shape name.// Determine object type with// switch & accordingly call

// calcArea() method.}}


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Required Switch Logic

switch ( _shape[i]->getType() ){

case L :

static_cast(_shape[i])->calcArea(); break;case C :

static_cast(_shape[i])

->calcArea(); break; }


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Delocalized Code

The above switch logic is same as was infunction drawArray()

Further we may need to draw shapes or

calculate area at more than one places incode


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Other Problems

Programmer may forget a check

May forget to test all the possible cases

Hard to maintain


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Polymorphism Revisited

In OO model, polymorphism means thatdifferent objects can behave in differentways for the same message (stimulus)

Consequently, sender of a message doesnot need to know the exact class of

receiver


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Virtual Functions

Target of a virtual function call isdetermined at run-time

In C++, we declare a function virtual by

preceding the function header withkeyword virtual

class Shape { virtual void draw();

}


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Shape Hierarchy

Shape

Line Circle Triangle

draw

calcArea

drawcalcArea

drawcalcArea

drawcalcArea


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Function printArea

void printArea(Shape* _shape[],int size) {

for (int i = 0; i < size; i++) {

// Print shape namecoutcalcArea();

cout


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Static vs Dynamic Binding

Static binding means that target functionfor a call is selected at compile time

Dynamic binding means that targetfunction for a call is selected at run time


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object oriented programming (oop) - cs304 power point slides lecture 28

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