多態

1.虛函數：

不一樣對象面對相同的操做會體現出各自不一樣的地方

靜態多態：早綁定，名字相同，參數不一樣，函數重載；同一個對象接受不一樣的操做

1 Class Rect{
2 
3 public:
4 
5  int calArea(int width);
6 
7  int calArea(int width,int height);
8 
9 }

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動態多態：晚綁定，以封裝和繼承爲基礎，；不一樣對象下達相同的操做，產生不一樣的實現；如何體現出這個多態

 1 class Shape{
 2   public:
 3      double calcArea(){
 4       cout<<"calcArea"<<endl;
 5   }
 6 };
 7 
 8 //圓類，繼承了Shape類
 9 class Circle :public Shape{
10     public:
11              Circle(double r);
12              double calcArea();
13     private:
14              double m_dR;
15 };
16 double Circle::calcArea(){
17    return 3.14*m_dR*m_dR;
18 }
19 
20 //矩形類，繼承了Shape類
21 class Rect : public Shape{
22       public:
23                Rect(double width,double height);
24                double calcArea();
25       private:
26                 m_dWidth;
27                 m_dHeight;
28 };
29 double Rect:: caclArea(){
30      return   m_dWidth* m_dHeight;
31 }
32 
33 int main(void){
34    Shape *shape1 = new Circle(4.0);//打印的是calcArea
35    Shape *shape2 = new Rect(3.0,5.0);//打印的是calcArea
36    ...
37    return 0;
38 }

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 1 class Shape{
 2    public:
 3       Shape();
 4       virtual double calcArea();//實現多態的函數定義爲virtual函數
 5       ~Shape();
 6 };
 7 Shape::Shape(){
 8     cout<<"Shape()"<<endl;
 9 }
10 Shape::~Shape(){
11     cout<<"~Shape()"<<endl;
12 }
13 double Shape:: calcArea(){
14     cout<< "Shape->calcArea"<<endl;
15 }
16 
17 class Circle:public Shape{
18 public:
19       Circle(double r);
20       virtual double calcArea();//可加可不加，最好加
21       ~Circle();
22 protected:
23       double m_radius;
24 };
25 Circle::Circle(double r){
26     m_radius = r;
27     cout<<"Circle"<<endl;
28 }
29 Circle::~Circle(){
30     cout<<"~Circle"<<endl;
31 }
32 double Circle::calcArea(){
33     cout<<"Circle->calcArea()"<<endl;
34     return 3.14*m_radius*m_radius;
35 }
36 
37 class Rect:public Shape{
38 public:
39     Rect(double width,double height);
40     ~Rect();
41     virtual double calcArea();//可加可不加，最好加
42 protected:
43     double m_dWidth;
44     double m_dHeight;
45 };
46 Rect::Rect(double width,double height){
47     m_dWidth=width;
48     m_dHeight=height;
49     cout<<"Rect()"<<endl;
50 }
51 Rect::~Rect(){
52     cout<<"~Rect()"<<endl;
53 }
54 double Rect::calcArea(){
55      cout<<"Rect->calcArea()"<<endl;
56     return m_dWidth*m_dHeight;
57 }
58 
59 
60 //使用，注意和上面的代碼做對比
61 #include<iostream>
62 #include<stdlib.h>
63 #include"Shape.h"
64 #include"Circle.h"
65 #include"Rect.h"
66 using namespace std;
67 
68 int main()
69 {
70     Shape *p1 = new Circle(2);
71     Shape *p2 = new Rect(2,3);
72 
73     p1->calcArea();//調用的應該是Circle的函數
74     p2->calcArea();//調用的應該是Rect的函數
75 
76     delete p1;
77     p1 = NULL;
78     delete p2;
79     p2 = NULL;
80    //Worker *p = new Worker();
81     //delete p;
82    // p = NULL;
83    // system("pause");
84     return 0;
85 }
86 
87 /*輸出結果
88 Shape()
89 Circle
90 Shape()
91 Rect()
92 Circle->calcArea()
93 Rect->calcArea()
94 ~Shape()
95 ~Shape()
96 */

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