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    发现很多朋友对于C#中的Abstract和Virtual函数区分得不是很清楚,下面我通过两段代码让大家看看这两者之间到底有什么区别~~

开发环境: VS.net 2005

使用方法: 用以下代码覆盖program.cs中的代码,然后run即可

第一段代码: Abstract的用法

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

namespace ConsoleApplication3
{
    public abstract class Book
    {
        //抽象方法，不含主体，抽象方法所在类必须为抽象类，派生类必须实现该方法
        public abstract void Introduce();
    }

    public interface iBook
    {
    }

    public class JavaBook : Book
    {
        //实现抽象方法，必须实现，必须添加override关键字
        public override void Introduce()
        {
            Console.WriteLine("I'm Java");
        }

//            // Compile Error
//            public void Introduce()
//            {
//                Console.WriteLine("I'm Java");
//            }
    }

    public class test
    {
        public test()
        {
            JavaBook javaBook = new JavaBook();
            javaBook.Introduce();      //将调用JavaBook中Introduce()
            Book book = new JavaBook();
            book.Introduce();      //将调用JavaBook中Introduce()
        }
        public static void Main()
        {
            test t = new test();
        }
    }
}

第二段代码: Virtual的用法以及override的用法

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

namespace ConsoleApplication2
{
    public abstract class Book
    {
        public virtual void Introduce()
        {
            Console.WriteLine("I'm book");
        }

        public virtual void SayHi()
        {
            Console.WriteLine("Hi, I'm book");
        }
    }

    public class JavaBook : Book
    {
        public override void Introduce()
        {
            Console.WriteLine("I'm Java");
        }

        //注意，此方法没有override父类的方法
        public void SayHi()
        {
            Console.WriteLine("Hi, I'm Java");
        }
    }

    public class test
    {
        public test()
        {
            JavaBook javaBook = new JavaBook();
            Book book = new JavaBook();
            javaBook.Introduce();       //将调用JavaBook中Introduce()
            book.Introduce();       //将调用JavaBook中Introduce()

            javaBook.SayHi();      //将调用JavaBook中SayHi()
            book.SayHi();           //将调用Book中SayHi()
        }

        public static void Main()
        {
            test t = new test();
        }
    }
}

第三段代码: new的用法

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

namespace ConsoleApplication4
{
    public abstract class Book
    {
        public void Introduce()
        {
            Console.WriteLine("I'm book");
        }

        public void SayHi()
        {
            Console.WriteLine("Hi, I'm book");
        }
    }

    public class JavaBook : Book
    {
        // 没有加new，但C#默认行为会加上new
        public void Introduce()
        {
            Console.WriteLine("I'm Java");
        }

        // 显式加上new，跟不加new实际效果一样，只是加new之后会消除compile warning
        public new void SayHi()
        {
            Console.WriteLine("Hi, I'm Java");
        }
    }

    public class test
    {
        public test()
        {
            JavaBook javaBook = new JavaBook();
            Book book = new JavaBook();

            javaBook.Introduce();       //将调用JavaBook中Introduce()
            javaBook.SayHi();           //将调用JavaBook中SayHi()
           
            book.Introduce();       //将调用Book中Introduce()
            book.SayHi();           //将调用Book中SayHi()
        }
        public static void Main()
        {
            test t = new test();
        }
    }
}