n Polymorph is m

7/24/2019 n Polymorph is m

1/32

NCST 1

Object Oriented Programming Using C++

Polymorphism

Polymorphism


2/32

NCST 2


Polymorphism

Static Binding

Method binding is at compile-time Pointer is Base* though it contains Deried

instance

Compiler sees Base*

Deried instance in!o aailable only at run-

time


3/32

NCST "


Polymorphism

Dynamic Binding

Methods should get bound at run-time #ae a per!ormance oerhead

C$$ does not dynamically bind till

e%plicitly as&ed

Special mechanism proided


4/32

NCST '


Polymorphism

virtual

Special construct De!ers method binding to run-time

Class has to tag a method as virtual

Method become irtual !or it and its

subclasses

(irtual cannot be )unirtualied+ by

subclasses


5/32

NCST ,


Polymorphism

Example

class Fruit {virtual void print();

};

class Apple { void print(); };

class Orange { void print(); };

Print

for ( items in bag ) bag.fruit->print()


6/32

NCST


Polymorphism

Polymorphism

Di!!erent ob.ects belonging to di!!erentclasses can respond to the same message in

di!!erent /ays0

Polymorphism allo/s a programmer to send

a message to an ob.ect /ithout concern

about ho/ the S is going to implementthe operation0


7/32NCST


Polymorphism

Polymorphism in C++

C$$ supports polymorphism at both early and

late binding0

3arly binding4static binding5

through operator and !unction oerloading0

6ate binding4dynamic binding5

through irtual !unctions 4pure polymorphism5

The ob.ects must be o! compatible types !or

polymorphism to /or&0

7n C$$ a public base class is compatible /ith its

deried classes0


8/32

NCST 8


Polymorphism

Polymorphism using Virtual Functions

class geom9ob. :

public ;000

irtual oid dra/4 5 < => ?* pure irtual *?@>

class circle ; public geom9ob. :public ;

000

oid dra/4 5> ?? dra/ circle

@>class line ; public geom9ob. :

public ;

oid dra/4 5> ?? dra/ line

@>


9/32

NCST A


Polymorphism

geom9ob. *gp>circle c>

line l>

000

gp < c> gp-dra/4 5> ?? Circle is dra/n

gp < l> gp-dra/4 5> ?? 6ine is dra/n

3%ample; sing (irtual Eunctions


10/32

NCST 1=


Polymorphism

Example: (contd

Feom9ob. *ob.9list GMHI9JBKL>?? array o! pointers to geometric ob.ects such circle

rectangle line 000 etc0

?? To dra/ all geom ob.ects in the ob.9list

!or 4i< => i MHI9JBK> i$$ 5

ob.9listGiL-dra/4 5> ?? dynamic binding used


11/32

NCST 11


Polymorphism

!"stract Class

Hn abstract class is one that is designed to representabstract concepts !or /hich ob.ects cannot e%ist0

7t is not used to create ob.ects0

H class /ith a Pure (irtual !unction is an abstract class0

3%ample;

class geom9ob. : ?? class geom9ob. is an abstract class

public ;

irtual oiddra/4 5 < => ?? pure irtual !unction

000

@>


12/32

NCST 12


Polymorphism

Pure Virtual

Hbstract class e%pressed using pure irtualmethods

=0added to the method

7ndicates method ispure virtual 7nstances o! classes /ith pure irtual

methods cannot be created


13/32

NCST 1"


Polymorphism

Pure Virtual

Subclass has to proide de!inition !or pureirtual method

i! not proided it also becomes an abstract

class

Obj O i d P i U i C


14/32

NCST 1'


Polymorphism

Example

// abstract classclass !ape {

virtual void dra"()#$; // pure virtual

};

class %ine & public !ape {

void dra"();

};

Obj t O i t d P i U i C


15/32

NCST 1,


Polymorphism

!"stract Class

Oepresents an abstract concept eg0 Class Shape

7t only de!ines an inter!ace /ithout giing

any implementationNo ob.ects created o! this class

sed as the base class in a class hierarchy

Deried classes proide implementation o!

inter!ace

Obj t O i t d P i U i C+


16/32

NCST 1


Polymorphism

Example: !"stract classHn operating system may hide details o! its deice

driers behind an abstract deice drier inter!ace

class character9deice :

public;irtual int open4 5 < =>

irtual int close4const char*5 < =>

irtual int read4const char* int5 < =>irtual int /rite4const char* int5 < =>

??

@>

Obj t O i t d P i U i C+


17/32

NCST 1


Polymorphism

Example

!ape s' s;!ape *ps';

%ine l';

ps' # +l';

ps'->dra"();

s.dra"();

Object Oriented Programming Using C+


18/32

NCST 18


Polymorphism

Example

!ape s' s; // error!ape *ps'; // ok

%ine l';

ps' # +l'; // ok

ps'->dra"(); // ok

s.dra"(); // error



19/32

NCST 1A


Polymorphism

Example

class !ape {virtual void dra"()#$;

};

class ,losed!ape & public !ape {

};

class ect & public ,losed!ape {

void dra"();

};



20/32

NCST 2=


Polymorphism

Example

!ape s' s;!ape *ps';

,losed!ape cs';

,losed!ape *pcs';

ect r';

ps' # +r';

pcs' # +r';

pcs'->dra"();



21/32

NCST 21


Polymorphism

Example

!ape s' s; // error!ape *ps'; // ok

,losed!ape cs'; // error

,losed!ape *pcs'; // ok

ect r';

ps' # +r';

pcs' # +r';

pcs'->dra"();



22/32

NCST 22


Polymorphism

Virtual Destructor

Deallocator may use sie o! ob.ect duringdeletion

Problem i! Base* contains Deried instance

sie o! Base /ill be used

Base destructor declared irtual

deallocator gets proper sie



23/32

NCST 2"


Polymorphism

Virtual Destructor

sed /hen custom allocation?deallocationused

Choices

either declare destructor as irtual

re!rain !rom using sie during deletion



24/32

NCST 2'


Polymorphism

Example

class {() { cout 0 ctor1n0; }

2() { cout 0 dtor1n0; }

};

class 3 & public {

3() { cout 03 ctor1n0; }

23() { cout 03 dtor1n0; }

};

* 4 # ne" 3;delete 4;



25/32

NCST 2,


Polymorphism

#utput

3%pected ctor

3 ctor

3 dtor

dtor

Hctual

ctor

3 ctor

dtor



26/32

NCST 2


Polymorphism

Example

class {() { cout 0 ctor1n0; }

virtual 2() { cout 0 dtor1n0; }

};



27/32

NCST 2


Polymorphism

$ip

Proide irtual destructor in all classes thatact as base class /hen deried type is

manipulated through base pointer



28/32

NCST 28


Polymorphism

Virtual Constructor

Not possible Constructor needs to &no/ e%act type o!

ob.ect to be created

Constructor is not a normal !unctionNot called on an e%isting ob.ect

Pointer to constructor not possible



29/32

NCST 2A

j g g g+

Polymorphism

Cloning

Similar !unctionality can be proided bye%plicit irtual !unction

(irtual !unction oerridden by subclasses

sed !or ob.ect )cloning+



30/32

NCST "=

j g g g+

Polymorphism

Example

class Fruit {virtual Fruit* clone()#$;

};

class Apple {

virtual Fruit* clone() {

return ne" Apple();

}

};



31/32

NCST "1

j g g g+

Polymorphism

Example

Fruit *f' *f;

f' # bag.fruit();

f # f'->clone(); // f2 is Apple if f1 is Apple*

// f2 is Orange if f1 is Orange*



32/32

NCST "2

j g g g+

P l hi

Diagrammatic %epresentation

Bag

o1

Eruit*

a1

Copy o!

a1

f'->clone()

Still an Apple

a1a1

n Polymorph is m

Documents

Transcript of n Polymorph is m