最简单的抽象类与多态

抽象类包含抽象成员（该成员不提供任何实现，但强迫子类对其实现），不可实例化。

多态：举个例子：同一个方法，在不同的子类中重写，然后统一调用，则呈现出不同的效果。

基类：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 
 6 namespace OverrideTest
 7 {
 8     //抽象类
 9    public abstract class PdaItem
10     {
11        public PdaItem(string name)
12        {
13            Name = name;
14        }
15        public virtual string Name { get; set; }
16        public abstract string GetSummary();//纯虚函数，强制子类实现，他也实现了多态
17     }
18 }

PdaItem

下面为两个子类：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 
 6 namespace OverrideTest
 7 {
 8     class Contacts:PdaItem
 9     {
10         public Contacts(string name)//继承父类的构造函数
11             : base(name)
12         {
13             Name = name;
14         }
15         public override string Name
16         {
17             get
18             {
19                 return FirstName + " " + LastName;  
20             }
21             set
22             {
23                 string[] names = value.Split(' ');
24                 FirstName = names[0];
25                 LastName = names[1];
26             }
27         }
28         public string FirstName { get; set; }
29         public string LastName { get; set; }
30         public string Address { get; set; }
31         public override string GetSummary()//强制重写
32         {
33             return string.Format("FirstName :{0}" + "LstName:{1}" + "Address:{2}", FirstName, LastName, Address);
34         }
35     }
36 }

Contacts:PdaItem

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 
 6 namespace OverrideTest
 7 {
 8     class Appointment:PdaItem
 9     {
10         public Appointment(string name):base(name)
11         {
12             Name = name;
13         }
14         public DateTime StartDateTime { get; set; }
15         public DateTime EndDateTime { get; set; }
16         public string Location { get; set; }
17         public override string GetSummary()//强制重写
18         {
19             return string.Format("Subject:{0}" + Environment.NewLine
20                 + "Start:{1}" + Environment.NewLine
21                 + "End:{2}" + Environment.NewLine
22                 + "Location:{3}",
23                 Name, StartDateTime, EndDateTime, Location
24                 );
25         }
26     }
27 }

Appointment:PdaItem

主函数中的实现：

 1 PdaItem[] pda = new PdaItem[3];
 2 
 3             Contacts contacts = new Contacts("Tom Li");
 4             contacts.Address = "Chongwen Road NananZone Chongqing City China";
 5             pda[0] = contacts;
 6 
 7             Appointment appointment = new Appointment("Tms Cli");
 8             appointment.StartDateTime = new DateTime(2014, 10, 10);
 9             appointment.EndDateTime = new DateTime(2014, 10, 11);
10             appointment.Location = "Chongqing Unibersity of Posts and Telecommunictions";
11             pda[1] = appointment;
12 
13             contacts = new Contacts("another one");
14             contacts.Address = "thrity-thress dormitory";
15             pda[2] = contacts;
16             List(pda);
17         }
18         public static void List(PdaItem[] items)
19         {
20             foreach (PdaItem item in items)
21             {
22                 Console.WriteLine("---------------------------");
23                 Console.WriteLine(item.GetSummary());//虽然调用的都是基类的同一个函数，但是基类的三个对象分别指向了不同的子类，所以他们都选择了各自的继承链里面重写的最远的那个。
24             }
25         }

Main

运行结果：