{key}面向对象程序设计-C++ polymorphism 【第十三次上课笔记】

 1 /*************************************************************************
 2     > File Name: polymorphism.cpp
 3     > Author: Jeremy Wu
 4     > Created Time: Mon 25 May 2015 10:04:07 AM CST
 5     > Function: tune every instrument
 6  ************************************************************************/
 7 
 8 //多态：一个接口，多种实现
 9 //发生多态现象的条件：
10 //    １．通过调用虚函数(基类中必须要有，派生类中可有可无建议加上)
11 //    ２．借助指针或者引用调用该虚函数
12 //
13 //虚函数只能是 非静态 成员函数
14 //如果类中有虚函数，最好把 析构函数 也定义为虚函数
15 //
16 //如果基类的析构函数是虚函数，由它派生的所有的派生类的析构函数都 自动 成为虚函数
17 // ·构造函数无法定义为虚函数
18 //
19 //基类可以指向它的所有的派生类
20 //相当于基类给所有的派生类提供了统一的接口
21 //一般不会直接创建基类的对象
22 //
23 //{ 抽象基类 }
24 //如果一个类中包含纯虚函数，就是抽象类
25 //抽象类无法创建对象
26 //如果需要 避免 创建基类对象，应该使用纯虚函数
27 
28 
29 
30 //接下来是一个例子，有一个基类叫做乐器类
31 //由它派生出Wind ， Brass 和 Gitar 三个类
32 
33 #include <iostream>
34 
35 using namespace std;
36 
37 class Instrument {
38 public:
39     virtual void play ();    //virtual 关键字
40     Instrument () { cout << "Instement () " << endl; }
41     virtual ~Instrument () { cout << "~Instement () " << endl; }
42 };
43 
44 void Instrument::play () {    //类的外部定义前不用加　virtual 关键字
45     cout << "Instrument::play ()" << endl;
46 }
47 
48 class Wind : public Instrument{
49     virtual void play () { cout << "Wind::play () " << endl; }    //派生类中 virtual 关键字可加可不加
50     ~Wind () { cout << "Wind::~Wind ()" << endl; }
51 };
52 
53 class Brass : public Instrument {
54     virtual void play () { cout << "Brass::play ()" << endl; }
55     ~Brass () { cout << "Brass::~Brass () " << endl; }
56 };
57 
58 class Gitar : public Instrument {
59     virtual void play () { cout << "Gitar::play ()" << endl; }
60     ~Gitar () { cout << "Gitar::~Gitar ()" << endl; }
61 };
62 
63 //inst 指针在定义的时候，是静态类型
64 //在程序运行过程中，它的动态类型就会根据指向对象的类型作改变
65 //
66 //有时候把动态绑定称为运行时绑定，也称后继绑定
67 //run-time binding
68 
69 void tune (Instrument * inst) {    //引用传递 或者用指针
70     inst->play ();                //Dynamic binding
71                                 //在编译时进行　动态绑定
72 }
73 
74 int main () {
75 
76     Instrument * p = new Gitar;
77     Instrument * p2 = new Wind;
78 
79     delete p;
80     delete p2;
81 
82     return 0;
83 }

 1 /*************************************************************************
 2     > File Name: ployPROB.cpp
 3     > Author: Jeremy Wu
 4     > Created Time: Mon 25 May 2015 10:50:07 AM CST
 5  ************************************************************************/
 6 
 7 //定义一个形状类的继承结构
 8 //
 9 //Shape -> Triangle
10 //        -> Rectangle
11 //        -> Circle
12 //
13 //给形状定义两个操作：
14 //    getArea ()　求面积
15 //    getLength () 求周长
16 
17 #include <iostream>
18 #include <cmath>
19 
20 const double PI = 3.1415926;
21 
22 using namespace std;
23 
24 class Shape {
25 public:
26     virtual double getArea () = 0;    
27     virtual double getLength () = 0;
28     virtual ~Shape () { cout << "~Shape ()" << endl; }
29     Shape () { cout << "Shape ()" << endl; }
30 };
31 
32 class Triangle : public Shape {
33 private:
34     double x, y, z;
35 public:
36     double getArea () { 
37         double p = (x + y + z) / 2.0;
38         return sqrt (p * (p - x) * (p - y) * (p - z));
39     }
40     double getLength () { return x + y + z; }
41     Triangle (double ix = 0.0, double iy = 0.0, double iz = 0.0) { 
42         x = ix, y = iy, z = iz;
43     }
44     ~Triangle () { cout << "~Triangle () " << endl; }
45 };
46 
47 class Rectangle : public Shape {
48 private:
49     double x, y;
50 public:
51     double getArea () { return x * y; }
52     double getLength () { return 2.0 * (x + y); }
53     Rectangle (double ix = 0.0, double iy = 0.0) {
54         x = ix, y = iy;
55     }
56     ~Rectangle () { cout << "~Rectangle () " << endl; }
57 };
58 
59 class Circle : public Shape {
60 private:
61     double r;
62 public:
63     double getArea () { return PI * r * r; }
64     double getLength () { return 2.0 * PI * r; }
65     Circle (double ir = 0.0) {
66         r = ir;
67     }
68     ~Circle () { cout << "~Circle ()" << endl; }
69 };
70 
71 void test (Shape & sp) {
72     cout << "/***********************************/" << endl;
73     cout << ‘\t‘ << "Area is " << sp.getArea () << endl;
74     cout << ‘\t‘ << "Length is " << sp.getLength () << endl;
75     cout << "/***********************************/" << endl;
76 }
77 
78 int main () {
79 
80     Circle p1 (3.0);
81     Rectangle p2 (3.0, 6.0);
82     Triangle p3 (1.0, 2.0, 1.5);
83 
84     test (p1);
85     test (p2);
86     test (p3);
87 
88     return 0;
89 }

 1 /*************************************************************************
 2     > File Name: example.cpp
 3     > Author: Jeremy Wu
 4     > Created Time: Mon 25 May 2015 11:34:47 AM CST
 5  ************************************************************************/
 6 
 7 #include <iostream>
 8 #include <cmath>
 9 
10 using namespace std;
11 
12 class Shape {
13 public:
14     virtual double area () = 0;    //不实现基类可以这么写，表示定义一个纯虚函数
15     virtual double zhou () = 0; //pure virtual function
16 };
17 
18 class Triangle : public Shape {
19     double a, b, c;
20 public:
21     Triangle (double aa, double bb, double cc) : a (aa), b (bb), c (cc) {}
22     virtual double area () {
23         double p = 0.5 * (a + b + c);
24         return sqrt (p * (p - a) * (p - b) * (p - c));
25     }
26     virtual double zhou () {
27         return a + b + c;
28     }
29 };
30 
31 class Rectangle : public Shape {
32     double a, b;
33 public:
34     Rectangle (double aa, double bb) : a (aa), b (bb) {}
35     virtual double area () {
36         return a * b;
37     }
38     virtual double zhou () {
39         return 2.0 * (a + b);
40     }
41 };
42 
43 class Circle : public Shape {
44     double r;
45 public:
46     Circle (double rr) : r (rr) {}
47     virtual double area () {
48         return 3.14159 * r * r;
49     }
50     virtual double zhou () {
51         return 2.0 * 3.14159 * r;
52     }
53 };
54 
55 void printArea (Shape * p) { 
56     cout << p->area () << endl; 
57 }
58 
59 void printZhou (Shape * p) {
60     cout << p->zhou () << endl;
61 }
62 
63 int main () {
64 
65     Shape * p1, * p2, * p3;
66     
67     //Shape sp;
68 
69     p1 = new Triangle (6, 7, 8);
70     p2 = new Rectangle (10, 4.6);
71     p3 = new Circle (5.8);
72 
73     printArea (p1);
74     printArea (p2);
75     printArea (p3);
76 
77     printZhou (p1);
78     printZhou (p2);
79     printZhou (p3);
80 
81     return 0;
82 }