C# 虚方法与抽象类

1.虚方法
将父类的方法标记为虚方法 ，使用关键字 virtual，这个函数可以被子类重新写一个遍。

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1. namespace _10多态练习
   
2. {
   
3.     class Program
   
4.     {
   
5.         static void Main(string[] args)
   
6.         {
   
7.             RealDuck rd = new RealDuck();
   
8.             MuDuck md = new MuDuck();
   
9.             XPDuck xd = new XPDuck();
   
10.             RealDuck[] ducks = { rd, md, xd };
    
11.             for (int i = 0; i < ducks.Length; i++)
    
12.             {
    
13.                 ducks[i].Bark();
    
14.             }
    
15.             Console.ReadKey();
    
16. 
    
17.         }
    
18.     }
    
19.     public class RealDuck
    
20.     {
    
21.         public virtual void Bark()
    
22.         {
    
23.             Console.WriteLine("真的鸭子嘎嘎叫");
    
24.         }
    
25.     }
    
26. 
    
27.     public class MuDuck : RealDuck
    
28.     {
    
29.         public override void Bark()
    
30.         {
    
31.             Console.WriteLine("木头鸭子吱吱叫");
    
32.         }
    
33.     }
    
34. 
    
35.     public class XPDuck : RealDuck
    
36.     {
    
37.         public override void Bark()
    
38.         {
    
39.             Console.WriteLine("橡皮鸭子唧唧叫");
    
40.         }
    
41.     }
    
42. }

2.抽象类
当父类中的方法不知道如何去实现的时候，可以考虑将父类写成抽象类，将方法写成抽象方法。

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1. namespace _12_抽象类
   
2. {
   
3.     class Program
   
4.     {
   
5.         static void Main(string[] args)
   
6.         {
   
7.             //使用多态求矩形的面积和周长以及圆形的面积和周长
   
8.             Shape shape = new Square(5, 6); //new Circle(5);
   
9.             double area = shape.GetArea();
   
10.             double perimeter = shape.GetPerimeter();
    
11.             Console.WriteLine("这个形状的面积是{0},周长是{1}", area, perimeter);
    
12.             Console.ReadKey();
    
13. 
    
14.         }
    
15.     }
    
16. 
    
17.     public abstract class Shape
    
18.     {
    
19.         public abstract double GetArea();
    
20.         public abstract double GetPerimeter();
    
21.     }
    
22.     public class Circle : Shape
    
23.     {
    
24. 
    
25.         private double _r;
    
26.         public double R
    
27.         {
    
28.             get { return _r; }
    
29.             set { _r = value; }
    
30.         }
    
31. 
    
32.         public Circle(double r)
    
33.         {
    
34.             this.R = r;
    
35.         }
    
36.         public override double GetArea()
    
37.         {
    
38.             return Math.PI * this.R * this.R;
    
39.         }
    
40. 
    
41.         public override double GetPerimeter()
    
42.         {
    
43.             return 2 * Math.PI * this.R;
    
44.         }
    
45.     }
    
46.     public class Square : Shape
    
47.     {
    
48.         private double _height;
    
49. 
    
50.         public double Height
    
51.         {
    
52.             get { return _height; }
    
53.             set { _height = value; }
    
54.         }
    
55. 
    
56.         private double _width;
    
57. 
    
58.         public double Width
    
59.         {
    
60.             get { return _width; }
    
61.             set { _width = value; }
    
62.         }
    
63. 
    
64.         public Square(double height, double width)
    
65.         {
    
66.             this.Height = height;
    
67.             this.Width = width;
    
68.         }
    
69. 
    
70.         public override double GetArea()
    
71.         {
    
72.             return this.Height * this.Width;
    
73.         }
    
74. 
    
75.         public override double GetPerimeter()
    
76.         {
    
77.             return (this.Height + this.Width) * 2;
    
78.         }
    
79.     }
    
80. 
    
81. }