Chuong 04 - Viec Khoi Tao Doi Tuong, Ham Ban, Lop Ban

VIC KHI TO I TNG, HM BN V

LP BN

ThS. Trn Anh Dng

Ni dung

i tng l thnh phn ca lp

i tng l thnh phn ca mng

i tng c cp pht ng

Hm bn

Lp bn

Cc nguyn tc xy dng lp

14/09/2014 Lp trnh hng i tng 2


i tng c th l thnh phn ca i tng

khc, khi mt i tng thuc lp ln c to

ra, cc thnh phn ca n cng c to ra.



Phng thc thit lp (nu c) s c t ng

gi cho cc i tng thnh phn.

Khi i tng kt hp b hy i tng thnh

phn ca n cng b hy, ngha l phng thc

hy b s c gi cho cc i tng thnh

phn, sau khi phng thc hy b ca i tng

kt hp c gi.



Nu i tng thnh phn phi cung cp tham

s khi thit lp th i tng kt hp (i tng

ln) phi c phng thc thit lp cung cp

tham s thit lp cho cc i tng thnh phn.

C php khi ng i tng thnh phn l

dng du hai chm (:) theo sau bi tn thnh

phn v tham s khi ng.


V d


class TamGiac{

Diem A, B, C;

public:

TamGiac(double xA, double yA, double xB, double yB,

double xC, double yC) : A(xA,yA), B(xB,yB),C(xC,yC){

}

void Ve();

// ...

};

TamGiac t(100,100,200,400,300,300);

{

V d


class TamGiac{

Diem A,B,C;

int loai;

public:

TamGiac(double xA, double yA, double xB, double yB,

double xC, double yC, int l): A(xA,yA), B(xB,yB),

C(xC,yC), loai(l) {

}

void Ve();

// ...

};

TamGiac t (100, 100, 200, 400, 300, 300, 1);

C php du hai chm cng c dng cho i tng thnh phn thuc kiu c s

?

V d


class Diem{

double x,y;

public:

Diem(double xx = 0, double yy = 0) : x(xx), y(yy){

}

void Set(double xx, double yy){

x = xx;

y = yy;

}

};

?


Khi mt mng c to ra cc phn t ca n

cng c to ra phng thc thit lp s

c gi cho tng phn t.

V khng th cung cp tham s khi ng cho tt

c cc phn t ca mng khi khai bo mng,

mi i tng trong mng phi c kh nng t

khi ng, ngha l c th thit lp khng cn

tham s.



i tng c kh nng t khi ng trong

nhng trng hp no?

1. Lp khng c phng thc thit lp

2. Lp c phng thc thit lp khng

tham s

3. Lp c phng thc thit lp m mi

tham s u c gi tr mc nhin




class Diem

{

double x,y;

public:

Diem(double xx, double yy) : x(xx), y(yy) { }

void Set(double xx, double yy) {

x = xx, y = yy;

}

// ...

};



class String {

char *p;

public:

String(char *s) { p = strdup(s); }

String(const String &s) { p = strdup(s.p); }

~String() {

cout



class SinhVien{

String MaSo;

String HoTen;

int NamSinh;

public:

SinhVien(char *ht, char *ms, int ns) : HoTen(ht),

MaSo(ms), NamSinh(ns){ }

};

String arrs[3];

Diem arrd[5];

SinhVien arrsv[7]; ?

Dng phng thc thit lp vi tham s c gi tr mc nhin


class Diem

{

double x,y;

public:

Diem(double xx = 0, double yy = 0) : x(xx), y(yy) { }

void Set(double xx, double yy) {

x = xx, y = yy;

}

// ...

};



class String{

char *p;

public:

String(char *s = "") { p = strdup(s); }

String(const String &s) { p = strdup(s.p); }

~String() {

cout



class SinhVien{

String MaSo, HoTen;

int NamSinh;

public:

SinhVien(char *ht=Nguyen Van A, char *ms=19920014, int ns = 1982) : HoTen(ht), MaSo(ms), NamSinh(ns) { }

};

String as[3];

Diem ad[5];

SinhVien asv[7];

?

Dng phng thc thit lp khng tham s


class Diem

{

double x,y;

public:

Diem(double xx, double yy) : x(xx), y(yy)

{ }

Diem() : x(0), y(0)

{ }

// ...

};



class String{

char *p;

public:

String(char *s) { p = strdup(s); }

String() { p = strdup(); }

~String() {

cout



class SinhVien {

String MaSo, HoTen;

int NamSinh;

public:

SinhVien(char *ht, char *ms, int ns) : HoTen(ht),

MaSo(ms), NamSinh(ns) { }

SinhVien() : HoTen(Nguyen Van A), MaSo(19920014), NamSinh(1982) { }

};

String as[3];

Diem ad[5];

SinhVien asv[7];

?

i tng c cp pht ng

i tng c cp pht ng l cc i tng

c to ra bng php ton new v b hy i

bng php ton delete

Php ton new cp i tng trong vng heap v

gi phng thc thit lp cho i tng c

cp.


i tng c cp pht ng


class String {

char *p;

public:

String( char *s ) { p = strdup(s); }

String( const String &s ) { p = strdup(s.p); }

~String() { delete [] p; }

//...

};

class Diem {

double x,y;

public:

Diem(double xx, double yy) : x(xx), y(yy) { }

//...

};

Cp pht v hy mt i tng


int *pi = new int;

int *pj = new int(15);

Diem *pd = new Diem(20,40);

String *pa = new String("Nguyen Van A");

//...

delete pa;

delete pd;

delete pj;

delete pi;

Cp pht v hy nhiu i tng

int *pai = new int[10];

Diem *pad = new Diem[5];

String *pas = new String[5];


?

Sai

Trong trng hp cp pht nhiu i tng, ta

khng th cung cp tham s cho tng phn t

c cp pht.

Cp v hy nhiu i tng

Thng bo li cho on chng trnh trn nh

sau:

Cannot find default constructor to initialize array

element of type 'Diem'

Cannot find default constructor to initialize array

element of type String

Khc phc li?


Li trn c khc phc bng cch cung cp phng

thc thit lp i tng c kh nng t khi ng.

Cp v hy nhiu i tng


class String{

char *p;

public:

String (char *s = "Alibaba") { p = strdup(s); }

String (const String &s) { p = strdup(s.p); }

~String () {delete [] p;}

//...

};

class Diem {

double x,y;

public:

Diem (double xx, double yy) : x(xx),y(yy){};

Diem () : x(0),y(0){};

};

Cp v hy nhiu i tng

Khi mi phn t c cp u c khi

ng vi cng gi tr.

int *pai = new int[10];

Diem *pad = new Diem[5];

//Ca 5 diem co cung toa do (0,0)

String *pas = new String[5];

//Ca 5 chuoi cung duoc khoi dong la Alibaba


Cp v hy nhiu i tng

Vic hy nhiu i tng c thc hin bng

cch dng delete v c thm du [] trc.

delete [] pas;

delete [] pad;

delete [] pai;

C th thay ba pht biu trn bng mt pht biu

duy nht sau hay khng?

delete pas,pad,pai;


Hm bn, lp bn

Gi s c lp Vector, lp Matrix

Cn vit hm nhn Vector vi mt Matrix

Hm nhn:

Khng th thuc lp Vector

Khng th thuc lp Matrix

Khng th t do

Gii php: Xy dng hm truy cp d liu?


Hm bn (Friend function)

Hm bn khng thuc lp. Tuy nhin, c

quyn truy cp cc thnh vin private.

Khi nh ngha mt lp, c th khai bo

mt hay nhiu hm bn (bn ngoi lp)

u im:

Kim sot cc truy nhp cp lp khng

th p t hm bn cho lp nu iu khng

c d tr trc trong khai bo ca lp. 14/09/2014 Lp trnh hng i tng 30

Hm bn (Friend function)

Cc tnh cht ca quan h friend:

Phi c cho, khng c nhn

Lp B l bn ca lp A, lp A phi khai bo r rng

B l bn ca n

Khng i xng

Khng bc cu


V d


class COUNTERCLASS{

int Counter;

public:

char CounterChar;

void Init( char );

void AddOne( ){

Counter++;

}

friend int Total (int);

};

V d


COUNTERCLASS MyCounter[26];

int Total(int NumberObjects)

{

for (int i=0, sum=0; i

Lp bn (Friend class)

Mt lp c th truy cp n cc thnh phn

c thuc tnh private ca mt lp khc.

thc hin c iu ny, chng ta c

th ly ton b mt lp lm bn (hm

friend) cho lp khc.


V d


class TOM{

public:

friend class JERRY; //C lp bn l JERRY

private:

int SecretTom; //B mt ca TOM

};

class JERRY{

public:

void Change(TOM T){

T.SecterTom++; //Bn nn c th thao th }

};

Giao din v chi tit ci t

Lp c hai phn tch ri

Phn giao din khai bo trong phn public ngi

s dng thy v s dng.

Chi tit ci t bao gm d liu khai bo trong phn

private ca lp v chi tit m ha cc hm thnh phn,

v hnh i vi ngi dng.

Lp ThoiDiem c th c ci t vi cc thnh

phn d liu l gi, pht, giy hoc tng s giy

tnh t 0 gi.


Giao din v chi tit ci t

Ta c th thay i uyn chuyn chi tit ci t,

ngha l c th thay i t chc d liu ca lp,

cng nh c th thay i chi tit thc hin cc

hm thnh phn (do s thay i t chc d liu

hoc ci tin gii thut). Nhng nu bo m

khng thay i phn giao din th khng nh

hng n ngi s dng, v do khng lm

v kin trc ca h thng.


Lp ThoiDiem Cch 1


class ThoiDiem{

int gio, phut, giay;

static bool HopLe(int g, int p, int gy);

public:

ThoiDiem(int g = 0, int p = 0, int gy = 0) {Set(g,p,gy);}

void Set(int g, int p, int gy);

int LayGio() const {return gio; }

int LayPhut() const {return phut; }

int LayGiay() const {return giay; }

void Nhap();

void Xuat() const;

void Tang();

void Giam();

};

Lp ThoiDiem Cch 2


class ThoiDiem{

long tsgiay;

static bool HopLe(int g, int p, int gy);

public:

ThoiDiem(int g = 0, int p = 0, int gy = 0) {Set(g,p,gy);}

void Set(int g, int p, int gy);

int LayGio() const {return tsgiay/3600;}

int LayPhut() const {return (tsgiay%3600)/60;}

int LayGiay() const {return tsgiay%60;}

void Nhap();

void Xuat() const;

void Tang();

void Giam();

};


Hnh thnh lp: Khi ta ngh n n nh mt

khi nim ring l Xy dng lp biu din khi

nim .

Lp l biu din c th ca mt khi nim v vy

tn lp lun l danh t.

Cc thuc tnh ca lp l cc thnh phn d liu

nn chng lun l danh t.

Cc hm thnh phn (cc hnh vi) l cc thao tc

ch r hot ng ca lp nn cc hm l ng t.




Problem

properties

Operation

(function,

method,

behavior)

Program

class XX

{ type1 prop1;

type2 prop2;

.......

type Method1(...)

{

}

.....

};

void main()

{ XX x; // object variable

x.Method(...);

}

pick

nouns

pick

verbs

Bao gi d liu v hnh vi thnh class


Cc thuc tnh c th suy din t nhng thuc

tnh khc th nn dng hm thnh phn thc

hin tnh ton.


class TamGiac{

Diem A,B,C;

double ChuVi;

double DienTich;

public:

//...

};

class TamGiac{

Diem A,B,C;

public:

//...

double ChuVi() const;

double DienTich() const;

};


Tuy nhin, nu cc thuc tnh suy din di hi

nhiu ti nguyn hoc thi gian thc hin tnh

ton, ta nn khai bo l d liu thnh phn.


class QuocGia{

long DanSo;

double DienTich;

double TuoiTrungBinh;

public:

double TinhTuoiTB() const;

//...

};


D liu thnh phn nn c kt hp:


class TamGiac{

Diem A,B,C;

public:

//...

};

class HinhTron{

Diem Tam;

double BanKinh;

public:

//...

};

class TamGiac{

double xA, yA;

double xB, yB, xC, yC;

public:

//...

};

class HinhTron{

double tx, ty, BanKinh;

public:

//...

};


Trong mi trng hp, nn c phng thc thit

lp (Constructor) khi ng i tng.

Nn c phng thc thit lp c kh nng t

khi ng khng cn tham s



Nu i tng c nhu cu cp pht ti nguyn th

phi c phng thc thit lp, copy constructor

khi ng i tng bng i tng cng

kiu v c destructor dn dp. Ngoi ra cn

c php gn (chng 5).

Nu i tng n gin khng cn ti nguyn

ring Khng cn copy constructor v destructor


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();


Documents

Chuong 04 - Viec Khoi Tao Doi Tuong, Ham Ban, Lop Ban