繼承的優(yōu)點

1、繼承的優(yōu)點,程式碼再使用 (code reuse)抽象概念再使用類別階層化澄清物件間的關(guān)係,繼承與Code Reuse(被動),主計劃,子計劃1,子計劃2,子計劃3,類別庫函式庫(.lib .dll),,,,,(你所在的組),繼承與Code Reuse,class List {……void insert() {…}void delete() {…}} ;,如果你對class list 感到 (1) 功能不

2、足 (2) 原有功能不佳,重新改寫??? (1) 原始碼在哪? (2) 還有其他使用者，是否都同意改寫?,繼承與Code Reuse,class List {….. insert(int n) ;…. delete(int pos);};class List1: public List {node& operator[](int index) ; //新增void insert(int n) ; // 修改:

3、更高效率的實作方式};void main() {List1 L;…..; L.insert(15) ;cout << L[3] ;},可能結(jié)果,主計劃,子計劃1(List1),子計劃2(List2),子計劃3(沿用List),類別庫(List,Stack…),,,,,繼承與Code Reuse(主動),[先修生]學號系級高中校名選課()註冊(),[僑生] 學號系級e-mail

4、國籍選課()註冊()工讀(),[交換學生]學號系級e-mail國籍選課()註冊()定期約談(),[一般生]學號系級e-mail選課()註冊()工讀(),Q: 設(shè)計一物件導向資料庫: 儲存學校學生資料,作業(yè): list ? stack,struct node {int info; node* next; };class list {node *head, *tail ; int node_no

5、 ;public:list() ;list(const node& n) ;list(const list& L) ;~list() ;int getSize() ;void insert(int pos, int value) ; // 0: first, node_no:lastvoid delete(int pos) ; // 刪除第pos個元素void show(string msg

6、) ; //印出串列內(nèi)容list& operator=(const list& L) ;friend list operator+(const list& L1, const list& L2) ; //聯(lián)集friend list operator*(const list& L1, const list& L2) ; //交集friend list operator-(co

7、nst list&L1, const list& L2) ; //差集} ;,使用list產(chǎn)生stack,class stack: public list {stack() ;~stack() ;operator=(const stack& s) ;void push(int x) ; //加在list的最前端int pop() ;//刪除list的第一個元素// list中的ope

8、rator+, -, * 是否也被繼承?} ;,測試class list,void main() {list L1, L2, L3 ;for (int i = 101; i=105; j--) L2.insert(L2.getSize(), j) ;L1.show(“L1=“); L2.show(“L2=“) ;L3 = L1 + L2 ;L3.show(“L3=L1+L2=“) ;L3 = L1 * L2;L

9、3.show(“L3=L1*L2=“) ;L3 = L1 – L2;L3.show(“L3=L1-L2=“) ;L3.delete(1) ; L3.delete(2) ; L3.show(“after 2 delete, L3=“) ;stack s1, s2 ;for (int k=1; k<=10; k++) { if (k%3==0) s1.pop();s1.push(k) ; s1.sho

10、w(“s1=“) ;}s2 = s1;s2.show(“s2=“) ;},第十章多型與虛擬函數(shù)(Polymorphism & Virtual Functions),10-1 衍生類別的指標10-2 簡介虛擬函數(shù)10-3 虛擬函數(shù)的細節(jié)10-4 應(yīng)用多型,多型,編譯時期多型(靜態(tài)多型)function overloading如何正確呼叫同名的函數(shù)? 利用參數(shù)個數(shù)與型態(tài)operator overloadi

11、ng其實同function overloading執(zhí)行時期多型 (或動態(tài)多型)如何正確呼叫不同物件的相同名稱的成員函數(shù) ? 利用繼承與多型,衍生類別與基底類別物件間的指定(assignment),class base { int x ; public: setx(int n) { x=n;} } ;class derived: public base {int y ;public:setx(int n) {

12、 base::setx(3*n);}sety(int n) { y = n;}} ;,void main() {base b ;derived d ;b = d ; // 可乎?b.setx(5) ;// 哪個setx()b.sety(10); //?d = b ; // ?d.setx(5) ; d.sety(8); // ?},結(jié)論,base Obj = derived Obj (可)der

13、ived Obj = base Obj (否),void main() {base b ;derived d ;b = d ; // 可b.setx(5) ; // 哪個setx()b.sety(10); //? 否d = b ; // ?否d.setx(5) ; d.sety(8); // ?可,10-1 衍生類別的指標,Case 1void main() {base *pb ;

14、base b; derived d ;pb = &b ; // Sure!pb->setx(5) ;pb = &d ; // 可乎?pb->setx(5) ; // 哪個?pb->sety(10); // ? 否},case 2void main() {derived *pd ;base b; derived d ;pd = &b ; // ??? 否

15、pd->setx(5) ; // ?否},衍生類別的參考(reference),Case 1void main() {base b; derived d ;base &refb1 = b ; // surerefb1.setx(5) ; // 哪個? basebase& refb2 = d ; // ?? 可 refb2.setx(5) ;refb2.sety(10);

16、// ?? 否},case 2void main() {base b; derived d ;derived &refd1 = b ; //?否refb1.setx(5) ;},結(jié)論: 自己寫,base-pointer = &derived-Obj (可)base-reference = derived-Obj (可),derived-pointer = &base-Obj (否)

17、derived-reference = base-Obj (否),10-2 多型與虛擬函數(shù),甚麼是執(zhí)行時期的多型?,void main() {Benz b; Volvo v; Civic c ;demo(b); demo(v); demo(c) ;}void demo(car& c) { c.move() ; c.stop() ;},class car { … move() ; …stop();} ;,clas

18、s Benz: public car {…move() ; …stop();} ;,class Volvo: public car {…move() ; …stop(); } ;,class Civic: public car {…move() ; … stop(); } ;,不使用虛擬函數(shù),class car {public:void move() { cout << “car move”;}} ;class Be

19、nz: public car {public:void move() { cout << “Benz move”;}} ;class Volvo: public car {public:void move() { cout << “Volvo move”;}} ;void demo(car& c) { c.move() ; } void main(){Benz b;Volvo v;dem

20、o(b);demo(v);},實際try!輸出結(jié)果為何? car move,甚麼是虛擬函數(shù)?,是一種宣告在基底類別中的成員函數(shù)提供執(zhí)行時期多型的機制使用virtual保留字通常衍生類別會override它,使用虛擬函數(shù) (配合reference),class car {virtual void move() { cout << “car move”;}} ;class Benz: public

21、 car {void move() { cout << “Benz move”;}} ;class Volvo: public car {void move() { cout << “Volvo move”;}} ;void demo(car& c) { c.move() ; } void main() { Benz b ;Volvo v; demo(b); demo(v) ; },實際

22、try!輸出結(jié)果為何? Benz move Volvo move,使用虛擬函數(shù)(配合pointer),class car {virtual void move() { cout move() ; } void main() { Benz b ;Volvo v; demo(&b); demo(&v) ; },實際try!輸出結(jié)果為何?

23、 Benz move Volvo move,使用虛擬函數(shù) (配合物件傳遞),class car {virtual void move() { cout << “car move”;}} ;class Benz: public car {void move() { cout << “Benz move”;}} ;class Volvo: pub

24、lic car {void move() { cout << “Benz move”;}} ;void demo(car c) { c.move() ; } void main() { Benz b ;Volvo v; demo(b); demo(v) ; },實際try!輸出結(jié)果為何? car move,不使用多型可以嗎?,多型: 一個介面多種用法void move(car& c)

25、{ c.move() ; ….} 不多型:void move(void *p, int type) {switch(type){case 1: ((Benz *)p)->move(); break ;case 2: ((Volvo *)p)->move(); break ;……}},練習,class plane {virtual void fly() { takeoff();

26、 onAir(); landing();}void onAir() {……}void takeoff() {……}void landing() {……}} ;// 你不滿意takeoff的行為該如何?,Plane,class plane{public:virtual void fly() { takeoff(); onAir(); landing();}void onAir() {cout<<&qu

27、ot;onAir"<<endl;}virtualvoid takeoff() {cout<<"takeoff"<<endl;}void landing() {cout<<"landing"<<endl;}};,class F16:public plane{public://void fly(){cout<&

28、lt;"F16 fly"<<endl;}void takeoff(){cout<<"F16 takeoff"<<endl;}};class B747:public plane{public://void fly(){cout<<"B747 fly"<<endl;}void takeoff(){cou

29、t<<"B747 takeoff"<<endl;}};,void demo(plane &p){p.fly();}void main(){ B747 b;F16 f;demo(b);demo(f);},Case Study: p. 10-19,#1,#2,#n,,,,,,head,store(x); retrieve();,#n,,#1,,stack,#1,

30、#2,#n,,,,如何利用list來模擬(實作) stack與queue,list,queue,,store,,retrieve,,,retrieve,store,繼承示意圖,class list {…virtual void store(int i) ;virtual int retrieve() ;} ;,class stack: public list {…void store(int i) ;int r

31、etrieve() ;} ;,class queue: public list {…void store(int i) ;int retrieve() ;} ;,,,10-3 更多虛擬函數(shù)的細節(jié),純粹虛擬函數(shù)(pure virtual function)class printer {string filename ;public:void reset() {… }virtual void print(in

32、t m)=0 ;},抽象類別(abstract class)當類別至少含有一個純粹虛擬函數(shù)時不能用來產(chǎn)生物件 e.g. printer p ; //XX,純粹虛擬函數(shù)的內(nèi)容,純粹虛擬函數(shù)(pure virtual function)class printer {string filename ;public:virtual void reset()=0;virtual void print(int mod

33、e)=0 ; },純粹虛擬函數(shù)的特性,衍生類別一定要override 基底類別中所有的純粹虛擬函數(shù)class printer {…...};class HPLaserJet6L: public printer {……void reset() { …自己的版本…}void print(int mode) {…自己的版本…}};,抽象類別的用途(一),設(shè)計共同的使用介面的類別(衍生類別負責實作)class shape

34、{string name ;public:virtual void draw(char b[][80])=0 ; // 不必有實作virtual void clear()=0 ; //不必有實作};class triangle: public shape {………} ;class circle: public shape {……};,抽象類別的用途(二),防止使用者產(chǎn)生不允許存在的物件class shape {

35、string name ;public:virtual void draw()=0 ;};class triangle: public shape {………} ;class circle: public shape {……};void main() { shape s ; /* what ??? */ ….. },10-4 應(yīng)用多型,早期繫結(jié)(early binding)或編譯時期繫結(jié)(compiling time bin

36、ding)一般函數(shù)超載函數(shù)夥伴函數(shù)非虛擬之成員函數(shù),晚期繫結(jié)(late binding)或執(zhí)行時期繫結(jié)(run-time binding)虛擬函數(shù) (效率較差),例子,early bindingvoid fun(int x) { cout << x;}void main() {fun(5) ; // early binding},late binding// 承前例void move(car&a

37、mp; c) {c.move() ; // late binding}void main() {Benz b; Volvo v ; int x ;cin >> x ;if (x%2) b.move(); …..,繼承與Code Reuse(主動),[先修生]學號系級高中校名選課()註冊(),[僑生] 學號系級e-mail國籍選課()註冊()工讀(),[交換學生]學號系級

38、e-mail國籍選課()註冊()定期約談(),[一般生]學號系級e-mail選課()註冊()工讀(),Q: 設(shè)計一物件導向資料庫: 儲存學校學生資料,練習,class student {protected:string studID, name, eMail ;public:void fillData()=0 ;void getID() { return ID; }void show()

39、=0 ;} ;class LocalStudent: public student {string ID ; ……}class AbroadStudent: public student {string passportID; string country ;……},續(xù),class IMStudents {const int MAX_STUD ;student *stud[720] ;public:stu