Chuong 03 - Lop Va Doi Tuong

CHNG 3. LP V I TNG

ThS. Trn Anh Dng

Ni dung

C php khai bo lp

nh ngha hm thnh phn ca lp

Khai bo v to lp i tng

Phm vi truy xut

Phng thc thit lp Constructor

Phng thc hy b Destructor

Phng thc Truy vn, Cp nht

Thnh vin tnh static member

14/09/2014 Lp trnh hng i tng 2

Lp trong C++

Mt lp bao gm cc thnh phn d liu (thuc

tnh) v cc phng thc (hm thnh phn).

Lp trong C++ thc cht l mt kiu d liu do

ngi s dng nh ngha.

Trong C++, dng t kha class ch im bt

u ca mt lp s c ci t.


Lp i tng

Lp l mt m t tru tng ca nhm cc i

tng cng bn cht, ngc li mi mt i

tng l mt th hin c th cho nhng m t

tru tng .


C php khai bo lp

class

{

//Thnh phn d liu

//Thnh phn x l

};


C php khai bo lp

class {

private:

protected:

public:

}; 14/09/2014 Lp trnh hng i tng 6

C php khai bo lp


class class_name

{

Access_Control_label:

members; (data & code)

Access_Control_label :

members; (data & code)

};

class Rectangle

{

private:

int width;

int length;

public:

void set(int w, int l);

int area();

};

Header

Cc thnh phn ca lp

Thuc tnh: Cc thuc tnh c khai bo

ging nh khai bo bin trong C

Phng thc: Cc phng thc c khai

bo ging nh khai bo hm trong C. C

hai cch nh ngha thi hnh ca mt

phng thc

nh ngha thi hnh trong lp

nh ngha thi hnh ngoi lp


C ch to lp cc lp

Xc nh cc thuc tnh (d liu)

Nhng g m ta bit v i tng ging nh

mt struct

Xc nh cc phng thc (hnh vi)

Nhng g m i tng c th lm

Xc nh cc quyn truy xut


nh ngha hm thnh phn

C php nh ngha cc hm thnh phn

bn ngoi khai bo lp:

:: ()

{

}

V d:

void point::display() {

//..

}


nh ngha hm thnh phn


class Rectangle{

private:

int width, length;

public:

void set (int w, int l);

int area() { return width*length; }

};

void Rectangle :: set (int w, int l)

{

width = w;

length = l;

}

inline

class name

member function name

scope operator

V d lp Time


class Time {

public:

void Set (int hours , int minutes , int seconds);

void Increment ( );

void Write ( ) const;

Time (int initHrs, int initMins, int initSecs ); //constructor

Time ( ); //default constructor

private: int hrs; int mins; int secs;

} ;

V d lp Time


Private data:

hrs

mins

secs

Set

Increment

Write

Time

Time

Time class


Khai bo v to i tng:

;

Gi hm thnh phn ca lp

. ();

();




class Rectangle

{

private:

int width;

int length;

public:


int area();

};

void main()

{

Rectangle r1;

r1.set(5, 8);

}

r1 is statically allocated

width

length

r1 width = 5

length = 8



class Rectangle

{

private:

int width;

int length;

public:


int area();

};

main()

{

Rectangle r1;

r1.set(5, 8);

Rectangle *r2; r2 = &r1;

r2->set(8,10);

}

r2 is a pointer to a Rectangle object

width

length

r1 width = 5

length = 8

5000

???

r2 6000

5000

width = 8

length = 10

//dot notation

//arrow notation



class Rectangle

{

private:

int width;

int length;

public:


int area();

};

main()

{

Rectangle *r3; r3 = new Rectangle();

r3->set(80,100);

delete r3; r3 = NULL;

}

r3 is dynamically allocated

???

r3 6000

NULL

//arrow notation

V d

Xy dng lp im (Point) trong hnh hc 2D

Thuc tnh

Tung

Honh

Thao tc (phng thc)

Khi to

Di chuyn

In ra mn hnh


V d


/*point.cpp*/

#include

using namespace std;

class point {

/*khai bo cc thnh phn d liu ring*/

private:

int x,y;

/*khai bo cc hm thnh phn cng cng*/

public:

void init(int ox, int oy);

void move(int dx, int dy);

void display();

};

V d


void point::init(int ox, int oy) {

cout

V d


void main()

{

point p;

p.init(2,4); /*gi hm thnh phn t i tng*/

p.display();

p.move(1,2);

p.display();

}

Ham thanh phan init

Ham thanh phan display

Toa do: 2 4

Ham thanh phan move

Ham thanh phan display

Toa do: 3 6

Phm vi truy xut

Trong nh ngha ca lp ta c th xc nh kh

nng truy xut thnh phn ca mt lp no t

bn ngoi phm vi lp.

private, protected v public l cc t kha xc

nh phm vi truy xut

Mi thnh phn c lit k trong phn public

u c th truy xut trong bt k hm no.

Nhng thnh phn c lit k trong phn

private ch c truy xut bn trong phm vi lp.


Phm vi truy xut

Trong lp c th c nhiu nhn private v public

Mi nhn ny c phm vi nh hng cho n khi

gp mt nhn k tip hoc ht khai bo lp.

Nhn private u tin c th b qua v C++ ngm

hiu rng cc thnh phn trc nhn public u

tin l private.


Phm vi truy xut V d


class TamGiac{

private:

float a,b,c;/* di ba cnh*/

public:

void Nhap();/*nhp vo di ba cnh*/

void In();/*in ra cc thng tin lin quan n tam gic*/

private:

int Loaitg();//cho bit kiu ca tam gic: 1-d,2-vc,3-c,4-v,5-t

float DienTich();/*tnh din tch ca tam gic*/

};

Phm vi truy xut V d


class TamGiac{

private:

float a,b,c;/* di ba cnh*/

int Loaitg();//cho bit kiu ca tam gic: 1-d,2-vc,3-c,4-

v,5-t

float DienTich();/*tnh din tch ca tam gic*/

public:

void Nhap();/*nhp vo di ba cnh*/

void In();/*in ra cc thng tin lin quan n tam gic*/

};

Tham s hm thnh phn

Hm thnh phn c quyn truy nhp n cc

thnh phn private ca i tng gi n


void point::init (int xx, int yy){

x = xx;

y = yy; //x, y la thanh phan cua lop point

}

?

Tham s hm thnh phn


int Trung (point pt){

return (x==pt.x && y==pt.y);

}

int Trung (point *pt){

return (x==ptx && y==pty);

}

int Trung (point &pt) {

return (x==pt.x && y==pt.y);

}

? Hm thnh phn c quyn truy cp n tt c

cc thnh phn private ca cc i tng, tham

chiu i tng hay con tr i tng c cng

kiu lp khi c dng l tham s hnh thc ca

n.

Con tr this

T kha this trong nh ngha ca cc hm thnh

phn lp dng xc nh a ch ca i tng

dng lm tham s ngm nh cho hm thnh

phn.

Con tr this tham chiu n i tng ang gi

hm thnh phn.

V d:

int Trung(point pt){

return (this x == pt.x && this y == pt.y);

} 14/09/2014 Lp trnh hng i tng 28

Php gn i tng

L vic sao chp gi tr cc thnh phn d

liu t i tng a sang i tng b tng

ng tng i mt

V d:

point a, b;

a.init(5,2);

b = a;


2 y

5

b a

x 5

2

x

y

Phng thc thip lp

Trong hu ht cc thut gii, gii quyt

mt vn thng phi thc hin cc

cng vic:

Khi to gi tr cho bin, cp pht vng b nh

ca bin con tr, m tp tin truy cp,

Hoc khi kt thc, chng ta phi thc hin qu

trnh ngc li nh: Thu hi vng b nh

cp pht, ng tp tin,


Phng thc thip lp

Cc ngn ng OOP c cc phng thc

thc hin cng vic ny mt cch t

ng gi l phng thc thit lp v

phng thc hy b.


Phng thc thip lp

Phng thc thit lp hay cn gi l constructor,

l mt loi phng thc c bit dng khi

to th hin ca lp.

Bt k mt i tng no c khai bo u

phi s dng mt hm thit lp khi to cc

gi tr thnh phn ca i tng.

Hm thit lp c khai bo ging nh mt

phng thc vi tn phng thc trng vi tn

lp v khng c gi tr tr v (k c void).

Constructor phi c thuc tnh public


Phng thc thip lp

Constructor c th c khai bo chng nh cc

hm C++ thng thng khc hay khng?

Constructor c th c khai bo vi cc tham

s c gi tr ngm nh hay khng?


V d


class point{

/*Khai bo cc thnh phn d liu*/

int x, y;

public:

point() { x = 0; y = 0; } /*Hm thit lp mc nh*/

point(int ox, int oy) { x = ox; y = oy; }/*Hm thit lp*/

void move (int dx, int dy);

void display();

};

point a(5,2);

point b;

point c(3); ?

V d


class point{


int x, y;

public:

point() { x = 0; y = 0; } /*Hm thit lp mc nh*/

point(int ox, int oy = 1){ x = ox; y = oy;}/*Hm thit lp*/


void display();

};

point a(5,2);

point b;

point c(3);

Phng thc thip lp mc nh

Constructor mc nh (default constructor) l

constructor c gi khi th hin c khai bo

m khng c i s no c cung cp

MyClass x;

MyClass* p = new MyClass;

Ngc li, nu tham s c cung cp ti khai

bo th hin, trnh bin dch s gi constructor

khc (overload)

MyClass x(5);

MyClass* p = new MyClass(5);



i vi constructor mc nh, nu ta khng cung

cp bt k constructor no, C++ s t sinh

constructor mc nh l mt phng thc rng.

Tuy nhin, nu ta khng nh ngha constructor

mc nh nhng li c cc constructor khc, trnh

bin dch s bo li khng tm thy constructor

mc nh nu ta khng cung cp tham s khi to

th hin.


V d


class point{


int x, y;

public:

point(int ox, int oy = 1){ x = ox; y = oy;}


void display();

};

point a(5,2);

point b;

point c(3);

Phng thc thip lp sao chp

Chng ta c th to i tng mi ging i

tng c mt s c im, khng phi hon ton

nh php gn bnh thng, hnh thc ging

nhau c nh ngha theo quan nim ca

ngi lp trnh. lm c vn ny, trong

cc ngn ng OOP cho php ta xy dng

phng thc thit lp sao chp.

y l phng thc thit lp c tham s l tham

chiu n i tng thuc chnh lp ny.




Trong phng thc thit lp sao chp c th ta

ch s dng mt s thnh phn no ca i

tng ta tham chiu gn ging nhau

Phng thc hy b

Phng thc hy b hay cn gi l destructor,

c gi ngay trc khi mt i tng b thu hi.

Destructor thng c dng thc hin vic

dn dp cn thit trc khi mt i tng b hy.


Phng thc hy b

Mt lp ch c duy nht mt Destructor

C php:

Phng thc Destructor c tn trng tn vi

tn lp v c du ~ t trc

Khng c gi tr tr v

c t ng gi thc hin khi i tng ht

phm vi s dng.

Destructor phi c thuc tnh public


V d


class vector{

int n; //s chiu

float *v; //vng nh ta

public:

vector(); //Hm thit lp khng tham s

vector(int size); //Hm thit lp mt tham s

vector(int size, float *a);

~vector(); //Hm hy b, lun lun khng c tham s

void display();

};

Thao tc vi d liu private

Khi mun truy xut d liu private t cc i

tng th phi lm th no?

Khi mun cp nht d liu private t cc i

tng th phi lm th no?


Phng thc Truy vn

C nhiu loi cu hi truy vn c th:

Truy vn n gin (gi tr ca x l bao nhiu?)

Truy vn iu kin (thnh vin x c > 10 khng?)

Truy vn dn xut (tng gi tr ca cc thnh vin x v

y l bao nhiu?)

c im quan trng ca phng thc truy vn

l n khng nn thay i trng thi hin ti ca

i tng


Phng thc Truy vn

i vi cc truy vn n gin, quy c t tn

phng thc nh sau: Tin t get, tip theo l

tn ca thnh vin cn truy vn

int getX();

int getSize();

Cc loi truy vn khc nn c tn c tnh m t

Truy vn iu kin nn c tin t is


Phng thc Cp nht

Thng thay i trng thi ca i tng

bng cch sa i mt hoc nhiu thnh vin d

liu ca i tng .

Dng n gin nht l gn mt gi tr no cho

mt thnh vin d liu.

i vi dng cp nht n gin, quy c t tn

nh sau: Dng tin t set km theo tn thnh

vin cn sa

int setX(int); 14/09/2014 Lp trnh hng i tng 47

Truy vn v Cp nht

Nu phng thc get/set ch c nhim v cho ta

c/ghi gi tr cho cc thnh vin d liu Quy

nh cc thnh vin private c ch li g?

Ngoi vic bo v cc nguyn tc ng gi, ta cn

kim tra xem gi tr mi cho thnh vin d liu c hp

l hay khng.

S dng phng thc truy vn cho php ta thc hin

vic kim tra trc khi thc s thay i gi tr ca

thnh vin.

Ch cho php cc d liu c th truy vn hay thay i

mi c truy cp n.


V d


int Student::setGPA (double newGPA){

if ((newGPA >= 0.0) && (newGPA gpa = newGPA;

return 0; // Return 0 to indicate success

}

else

{

return -1; // Return -1 to indicate failure

}

}


Trong C, static xut hin trc d liu c khai

bo trong mt hm no th gi tr ca d liu

vn c lu li nh mt bin ton cc.

Trong C++, nu static xut hin trc mt d liu

hoc mt phng thc ca lp th gi tr ca n

vn c lu li v c ngha cho i tng

khc ca cng lp ny.

Cc thnh vin static c th l public, private

hoc protected.



i vi class, static dng khai bo thnh vin

d liu dng chung cho mi th hin ca lp:

Mt bn duy nht tn ti trong sut qu trnh

chy ca chng trnh.

Dng chung cho tt c cc th hin ca lp.

Bt k lp c bao nhiu th hin.


V d


class Rectangle

{

private:

int width;

int length;

static int count;

public:


int area();

}

Rectangle r1; Rectangle r2; Rectangle r3;

width

length

width

length

width

length

r1

r3

r2

count

V d

m s i tng MyClass:


class MyClass{

public:

MyClass();

~MyClass();

void printCount();

private:

static int count;

};

V d


int MyClass::count = 0;

MyClass::MyClass(){

this count++;

}

MyClass::~MyClass(){

this count--;

}

void MyClass::printCount(){

cout

V d


void main()

{

MyClass* x = new MyClass;

x printCount();

MyClass* y = new MyClass;

x printCount();

y printCount();

delete x;

y printCount();

}


Phng thc static?

i vi cc phng thc static, ngoi ngha

tng t vi d liu, cn c s khc bit c

bn l vic cho php truy cp n cc

phng thc static khi cha khai bo i

tng (thng qua tn lp)



Cc thnh vin lp tnh public c th c truy

cp thng qua bt k i tng no ca lp ,

hoc chng c th c truy cp thng qua tn

lp s dng ton t nh phm vi.

Cc thnh vin lp tnh private v protected phi

c truy cp thng qua cc hm thnh vin

public ca lp hoc thng qua cc friend ca lp.

Cc thnh vin lp tnh tn ti ngay c khi i

tng ca lp khng tn ti.



truy cp mt thnh vin lp tnh public khi cc

i tng ca lp khng tn ti, n gin thm

vo u tn lp v ton t nh phm vi cho

thnh vin d liu.

truy cp mt thnh vin lp tnh private hoc

protected khi cc i tng ca lp khng tn ti,

mt hm thnh vin public phi c cung cp

v hm phi c gi bi thm vo u tn ca

n vi tn lp v ton t nh phm vi.


V d v i tng ton cc

Xt on chng trnh sau:

#include

void main(){

cout

V d v i tng ton cc


#include

class Dummy{

public:

Dummy(){cout

Bi tp

Vit chng trnh cho php nhp, xut, khi to

1 hc sinh. Thng tin cn quan tm v 1 hc sinh:

M hc sinh (8 k t), h tn hc sinh (30 k t),

im ton (int), im vn (int).

Danh t: Hc sinh cu trc HS

ng t:

Nhp mt hs Hm Nhap()

Xut mt hs Hm Xuat();


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Chuong 03 - Lop Va Doi Tuong