Chuong 06 - Ke Thua

CHNG 6. K THA

ThS. Trn Anh Dng

Ni dung

14/09/2014 Lp trnh hng i tng 2

Quan h gia cc lp i tng 1

K tha 2

K tha n 3

Phm vi truy xut trong k tha 4

a k tha 5 5

Quan h gia cc lp i tng

Gia cc lp i tng c nhng loi quan

h sau:

Quan h mt mt (1-1)

Quan h mt nhiu (1-n)

Quan h nhiu nhiu (n-n)

Quan h c bit ha, tng qut ha


Quan h mt mt (1-1)

Khi nim: Hai lp i tng c gi l

c quan h mt-mt vi nhau khi mt i

tng thuc lp ny quan h vi mt i

tng thuc lp kia v mt i tng thuc

lp kia c quan h duy nht vi mt i

tng thuc lp ny.

K hiu:


ClassA ClassB Quan h

Quan h mt mt (1-1)

V d:


LOPHOC GIAOVIEN Ch nhim

VO CHONG Hn nhn

COUNTRY CAPITAL C


Khi nim: Hai lp i tng c gi l

c quan h mt-nhiu vi nhau khi mt i

tng thuc lp ny quan h vi nhiu i

tng thuc lp kia v mt i tng lp

kia c quan h duy nht vi mt i tng

thuc lp ny.

K hiu:




V d:


LOPHOC HOCSINH C

CONGTY NHANVIEN C

HOASI TACPHAM Sng tc


Khi nim: hai lp i tng c gi l

quan h nhiu-nhiu vi nhau khi mt i

tng thuc lp ny c quan h vi nhiu

i tng thuc lp kia v mt i tng

lp kia cng c quan h vi nhiu i

tng thuc lp ny.

K hiu




V d


NAM NU Yu

BACSI BENHNHAN Khm bnh

Quan h c bit ha tng qut ha

Khi nim: hai lp i tng c gi l

c quan h c bit ha-tng qut ha vi

nhau khi lp i tng ny l trng hp

c bit ca lp i tng kia v lp i

tng kia l trng hp tng qut ca lp

i tng ny.

K kiu:


ClassA

ClassB


V d:


TAMGIAC

TAMGIACCAN

NGUOI

SINHVIEN



Triangle

Polygon

Animal

Cat Horse Chicken

TerrestrialAnimal AquaticAnimal

Fish Octopus

Rectangle

K tha

K tha l mt c im ca ngn ng dng

biu din mi quan h c bit ha tng qut

ha gia cc lp. Cc lp c tru tng ha

v c t chc thnh mt s phn cp lp.

S k tha l mt mc cao hn ca tru tng

ha, cung cp mt c ch gom chung cc lp c

lin quan vi nhau thnh mt mc khi qut ha

c trng cho ton b cc lp ni trn.


K tha

Cc lp vi cc c im tng t nhau c th

c t chc thnh mt s phn cp k tha

(cy k tha).

Quan h l 1: K tha c s dng thng

dng nht biu din quan h l 1.

Mt sinh vin l mt ngi

Mt hnh trn l mt hnh ellipse

Mt tam gic l mt a gic


Li ch k tha

K tha cho php xy dng lp mi t lp c.

K tha cho php t chc cc lp chia s m

chng trnh chung, nh vy c th d dng sa

cha, nng cp h thng.

Trong C++, k tha cn nh ngha s tng

thch, nh ta c c ch chuyn kiu t ng.


c tnh K tha


Cho php nh ngha lp mi t lp c.

Lp mi gi l lp con (subclass) hay lp dn xut

(derived class)

Lp c gi l lp cha (superclass) hay lp c s

(base class).

c tnh K tha

Tha k cho php:

Nhiu lp c th dn xut t mt lp c s

Mt lp c th l dn xut ca nhiu lp c s

Tha k khng ch gii hn mt mc: Mt lp

dn xut c th l lp c s cho cc lp dn xut

khc


Animal

Cat Horse Chicken

TerrestrialAnimal AquaticAnimal

Fish Octopus

C php khai bo k tha

class SuperClass{

//Thnh phn ca lp c s

};

class DerivedClass : public/protected/private

SusperClass{

//Thnh phn b sung ca lp dn xut

};


Truy cp thnh vin ca lp


K tha n

Xt hai khi nim Ngi v Sinh vin vi mi

quan h t nhin: Mt Sinh vin l mt Ngi.

Trong C++, ta c th biu din khi nim trn,

mt sinh vin l mt ngi c thm mt s thng

tin v mt s thao tc (ring bit ca sinh vin).

Nh vy, ta t chc lp Sinh vin k tha t lp

Ngi.


K tha n

Ta c th t chc hai lp Nam sinh v N sinh l

hai lp con (lp dn xut) ca lp Sinh vin.

Trng hp ny, lp Sinh vin tr thnh lp cha

(lp c s) ca hai lp trn.


NGI

GING VIN SINH VIN

NAM SINH N SINH

K tha n V d


class Nguoi {

char *HoTen;

int NamSinh;

public:

Nguoi();

Nguoi( char *ht, int ns):NamSinh(ns) {HoTen=strdup(ht);}

~Nguoi() {delete [ ] HoTen;}

void An() const { cout

K tha n V d


class SinhVien : public Nguoi {

char *MaSo;

public:

SinhVien();

SinhVien( char *ht, char *ms, int ns) : Nguoi(ht,ns) {

MaSo = strdup(ms);

}

~SinhVien() {

delete [ ] MaSo;

}

void Xuat() const;

};

K tha n V d


void Nguoi::Xuat() const

{

cout

K tha n V d


void main() {

Nguoi p1("Le Van Nhan",1980);

SinhVien s1("Vo Vien Sinh", "200002541",1984);

cout

K tha c tnh ca lp cha

Khai bo


//...

};

Cho bit lp Sinh vin k tha t lp Ngi. Khi

Sinh vin tha hng cc c tnh ca lp Ngi.

V mt d liu: Mi i tng Sinh vin t ng

c thnh phn d liu h tn, nm sinh ca

ngi.


K tha c tnh ca lp cha

V mt thao tc: Lp Sinh vin c t ng k

tha cc thao tc ca lp cha. y chnh l kh

nng s dng li m chng trnh.

Ring phng thc thit lp khng c k

tha.

Kh nng tha hng cc thao tc ca lp c s

c th c truyn qua v hn mc.


nh ngha li thao tc lp con

Ta c th nh ngha li cc c tnh lp con

c lp cha, vic nh ngha ch yu l thao tc.



char *MaSo;

public:

//...

void Xuat() const;

};

void SinhVien::Xuat() const {

cout

Rng buc ng ngha lp con

C th p dng quan h k tha mang ngha

rng buc, i tng lp con l i tng

lp cha nhng c d liu b rng buc:

Hnh trn l Ellipse vi rng buc bn knh ngang dc

bng nhau.

S o l s phc vi rng buc phn o bng 0

Lp s o sau y l mt v d minh ha.


V d


class Complex {

friend ostream& operator

V d


class Imag: public Complex {

public:

Imag(double i = 0):Complex(0, i){ }

Imag(const Complex &c) : Complex(0, c.im){ }

Imag& operator = (const Complex &c){

re = 0; im = c.im;

return *this;

}

double Norm() const {

return fabs(im);

}

};

V d


void main()

{

Imag i = 1;

Complex z1(1,1)

Complex z3 = z1 - i; // z3 = (1,0)

i = Complex(5,2); // i la so ao (0,2)

Imag j = z1; // j la so ao (0,1)

cout

Rng buc ng ngha lp con

Trong v d trn, lp s o (Imag) k tha hu

ht cc thao tc ca lp s phc (Complex).

Tuy nhin, ta mun rng buc mi i tng

thuc lp s o u phi c phn thc bng 0. V

vy, phi nh ngha li cc hm thnh phn c

th vi phm iu ny.

V d php ton gn phi c nh ngha li

m bo rng buc ny.


Phm vi truy xut

Khi thit lp quan h k tha, ta vn phi

quan tm n tnh ng gi v che du

thng tin.

iu ny nh hng n phm vi truy xut

ca cc thnh phn ca lp.

Hai vn c t ra l:

Truy xut theo chiu dc Truy xut theo chiu ngang


Phm vi truy xut

Truy xut theo chiu dc:

Hm thnh phn ca lp con c quyn truy

xut cc thnh phn ca lp cha hay khng?

Truy xut theo chiu ngang:

Cc thnh phn ca lp cha, sau khi k tha

xung lp con, th th gii bn ngoi c quyn

truy xut thng qua i tng ca lp con hay

khng?


Truy xut theo chiu dc

Lp con c quyn truy xut cc thnh phn

ca lp cha hay khng, hon ton do lp

cha quyt nh. iu c xc nh

bng thuc tnh k tha.

Trong trng hp lp Sinh vin k tha lp

Ngi, Sinh vin c quyn truy xut h tn ca

chnh mnh (c khai bo lp Ngi) hay

khng?


Phm vi truy xut


class A{

private:

int a;

void f();

protected:

int b;

void g();

public:

int c;

void h();

};

void A::f()

{

a = 1; b = 2; c = 3;

}

void A::g()

{

a = 4; b = 5; c = 6;

}

void A::h(){

a = 7; b = 8; c = 9;

}

Phm vi truy xut


void main()

{

A x;

x.a = 10;

x.f();

V d: Cho bit trong on chng trnh

sau cu lnh no ng, cu lnh no sai.

x.b = 20;

x.g();

x.c = 30;

x.h();

}

Phm vi truy xut

Thuc tnh public:

Thnh phn no c thuc tnh public th c th truy

xut t bt c ni no.

Thuc tnh private: Thnh phn c thuc tnh

private

L ring t ca lp

Ch c hm thnh phn ca lp v ngoi l cc hm

bn c php truy xut.

Cc lp con cng khng c quyn truy xut


Phm vi truy xut

Thuc tnh protected:

Cho php qui nh mt vi thnh phn no ca lp

l bo mt, theo ngha th gii bn ngoi khng c

php truy xut, nhng tt c cc lp con, chu u

c php truy xut.


V d Thuc tnh private


class Nguoi {

char *HoTen;

int NamSinh;

public:

//...

};


char *MaSo;

public:

//...

void Xuat() const;

};

Thuc tnh private

Trong v d trn, khng c hm thnh phn no

ca lp SinhVien c th truy xut cc thnh phn

HoTen, NamSinh ca lp Nguoi.

V d, on chng trnh sau y s gy ra li:

void SinhVien::Xuat() const {

cout

Thuc tnh private

Ta c th khc phc li trn nh khai bo lp

SinhVien l bn ca lp Nguoi nh trong v d

ban u:


class Nguoi {

friend class SinhVien;

char *HoTen;

int NamSinh;

public:

//...

};

Thuc tnh private

Khai bo lp bn nh trn, lp SinhVien c th

truy xut cc thnh phn private ca lp Nguoi.

Cch lm trn ch gii quyt c nhu cu ca

ngi s dng khi mun to lp con c quyn

truy xut cc thnh phn d liu private ca lp

cha.

Tuy nhin, cn phi sa li lp cha v tt c cc

lp cp cao hn mi khi c mt lp con mi.


Thuc tnh private


class Nguoi {

friend class SinhVien;

friend class NuSinh;

char *HoTen; int NamSinh;

public:

//...

void An() const { cout

Thuc tnh protected

Trong v d trc, khi ci t lp NuSinh ta phi

thay i lp cha SinhVien v c lp c s Nguoi

mc cao hn.


class Nguoi {

protected:

char *HoTen;

int NamSinh;

public:

//...

};

Thuc tnh protected



protected:

char *MaSo;

public:

SinhVien(char *ht, char *ms, int ns) : Nguoi(ht,ns){

MaSo = strdup(ms);

}

~SinhVien(){

delete [ ] MaSo;

}

void Xuat() const;

};

Thuc tnh protected


class NuSinh : public SinhVien {

public:

NuSinh(char *ht, char *ms, int ns) : SinhVien(ht,ms,ns){

}

void An() const {

cout

Thuc tnh protected


void Nguoi::Xuat() const {

cout

Thuc tnh protected

L cch trnh phi sa i lp c s khi c

lp con mi hnh thnh m bo tnh ng gi.

Thng thng ta dng thuc tnh protected cho

thnh phn d liu v public cho thnh phn

phng thc.

Tm ti, thnh phn c thuc tnh protected ch

cho php nhng lp con k tha c php s

dng.


Truy xut theo chiu ngang

Thnh phn protected v public ca lp khi k

tha xung lp con th th gii bn ngoi c

quyn truy xut thng qua i tng thuc lp

con hay khng?

iu ny hon ton do lp con quyt nh

bng phm vi k tha: K tha public, K tha

protected, K tha private


Phm vi truy xut trong k tha


private

private private private

protected

protected protected protected

public

public public public

D1: public B D3: protected B

D2: private B



private Protected public

private ? ? ?

protected ? ? ?

public ? ? ?

Type of Inheritance

Acce

ss C

on

trol fo

r Mem

bers



Type of inheritance Base class member access specifier

public

inheritance protected

inheritance private

inheritance

Public

public in derived class.

Can be accessed directly by any

non-static member functions,

friend functions and non-

member functions.

protected in derived class.

Can be accessed directly by all

non-static member functions

and friend functions.

private in derived class.




Protected









private in derived class.




Private

Hidden in derived class.

Can be accessed by non-static

member functions and friend

functions through public or

protected member functions

of the base class.






of the base class.






of the base class.

V d 1


mother

daughter son

class mother{

protected:

int x, y;

public:

void set(int a, int b);

private:

int z;

};

class daughter : public mother{

private:

double a;

public:

void foo ( );

};

void daughter :: foo ( ){

x = y = 20;

set(5, 10);

cout

V d 2


mother

daughter son

class mother{

protected:

int x, y;

public:

void set(int a, int b);

private:

int z;

};

class son : private mother{

private:

double b;

public:

void foo ( );

};

void son :: foo ( ){

x = y = 20;

set(5, 10);

cout

Phng thc thit lp

Phng thc thit lp ca lp c s lun lun

c gi mi khi c mt i tng ca lp dn

xut c to ra.

Nu mi phng thc thit lp ca lp c s u

i hi phi cung cp tham s th lp con bt

buc phi c phng thc thit lp cung cp

cc tham s


Phng thc thit lp

V d 1:


class A {

public:

A ( )

{ cout

Phng thc thit lp

V d 2:


class A {

public:

A ( )

{ cout

nh ngha cc thnh phn ring

Ngoi cc thnh phn c k tha, lp dn

xut c th nh ngha thm cc thnh phn ring


class HinhTron : Diem {

double r;

public:

HinhTron( double tx, double ty, double rr) : Diem(tx, ty){

r = rr;

}

void Ve(int color) const;

void TinhTien( double dx, double dy) const;

};

HinhTron t(200,200,50);

nh ngha cc thnh phn ring

Lp dn xut cng c th override cc phng

thc c nh ngha trong lp cha.


class A {

protected:

int x, y;

public:

void print (){

cout

Truy cp phng thc


class Point{

protected:

int x, y;

public:

void set(int a, int b)

{ x=a; y=b; }

void foo ();

void print();

};

class Circle : public Point{

private: double r;

public:

void set (int a, int b, double c) {

Point ::set(a, b); //same name function call

r = c;

}

void print() { //.. }

};

Circle C;

C.set(10,10,100); ???

C.foo (); ???

C.print(); ???

Point A;

A.set(30,50); ???

A.print();

Phng thc hy b

Khi mt i tng b hy i, phng thc hy b

ca n s c gi. Sau , cc phng thc

hy b ca lp c s s c gi mt cch t

ng.

V vy, lp con khng cn v cng khng c

thc hin cc thao tc dn dp cho cc thnh

phn thuc lp cha.


Phng thc hy b - V d



char *MaSo;

public:

SinhVien( char *ht, char *ms, int ns) : Nguoi(ht,ns){ MaSo = strdup(ms);

}

SinhVien(const SinhVien &s) : Nguoi(s){

MaSo = strdup(s.MaSo);

}

~SinhVien() {delete [ ] MaSo;}

//...

};

Con tr v k tha

Con tr trong k tha hot ng theo nguyn tc

sau:

Con tr tr n i tng thuc lp c s th c th tr

n cc i tng thuc lp con.

Nhng con tr tr n i tng thuc lp con th

khng th tr n cc i tng thuc lp c s.

C th p kiu con tr tr n i tng thuc lp

con c th tr n i tng thuc lp c s. Tuy

nhin thao tc ny c th nguy him.


a k tha

a k tha cho php mt lp c th l dn xut

ca nhiu lp c s.

class A : public B, public C {

};

Cc c im ca k tha n vn ng cho

trng hp a k tha.


a k tha

Lm th no biu th tnh c lp ca cc thnh

phn cng tn bn trong mt lp dn xut?

Cc phng thc thit lp v hy b c gi

nh th no: th t, truyn thng tin, ?

Lm th no gii quyt tnh trng tha k xung

t trong , lp D dn xut t B v C, v c hai

cng l dn xut ca A


a k tha V d


class BASE_A{

public:

int a;

int f( ){

return 0;

}

int g( ){

return 0;

}

int h( ) { return 0;}

};

class BASE_B

{

public:

int a;

int f( ){

return 0;

}

int g( ){

return 0;

}

};

a k tha V d


class ClassC : public BASE_A, public BASE_B{

//

};

void main(){

ClassC C;

C.f = g; //Li m h

C.a = 1; //Li m h

C.g(); //Li m h

C.h();

}

Chuong 06 - Ke Thua

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