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：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace OverrideTest
{
    //抽象类
   public abstract class PdaItem
    {
       public PdaItem(string name)
       {
           Name = name;
       }
       public virtual string Name { get; set; }
       public abstract string GetSummary();//纯虚函数，强制子类实现，他也实现了多态
    }
}

下面为两个子类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace OverrideTest
{
    class Contacts:PdaItem
    {
        public Contacts(string name)//继承父类的构造函数
            : base(name)
        {
            Name = name;
        }
        public override string Name
        {
            get
            {
                return FirstName + " " + LastName;  
            }
            set
            {
                string[] names = value.Split(' ');
                FirstName = names[0];
                LastName = names[1];
            }
        }
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string Address { get; set; }
        public override string GetSummary()//强制重写
        {
            return string.Format("FirstName :{0}" + "LstName:{1}" + "Address:{2}", FirstName, LastName, Address);
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace OverrideTest
{
    class Appointment:PdaItem
    {
        public Appointment(string name):base(name)
        {
            Name = name;
        }
        public DateTime StartDateTime { get; set; }
        public DateTime EndDateTime { get; set; }
        public string Location { get; set; }
        public override string GetSummary()//强制重写
        {
            return string.Format("Subject:{0}" + Environment.NewLine
                + "Start:{1}" + Environment.NewLine
                + "End:{2}" + Environment.NewLine
                + "Location:{3}",
                Name, StartDateTime, EndDateTime, Location
                );
        }
    }
}

主函数中的实现：

PdaItem[] pda = new PdaItem[3];

            Contacts contacts = new Contacts("Tom Li");
            contacts.Address = "Chongwen Road NananZone Chongqing City China";
            pda[0] = contacts;

            Appointment appointment = new Appointment("Tms Cli");
            appointment.StartDateTime = new DateTime(2014, 10, 10);
            appointment.EndDateTime = new DateTime(2014, 10, 11);
            appointment.Location = "Chongqing Unibersity of Posts and Telecommunictions";
            pda[1] = appointment;

            contacts = new Contacts("another one");
            contacts.Address = "thrity-thress dormitory";
            pda[2] = contacts;
            List(pda);
        }
        public static void List(PdaItem[] items)
        {
            foreach (PdaItem item in items)
            {
                Console.WriteLine("---------------------------");
                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。
            }
        }

运行结果：