轉載-區分C#中的Abstract函數和Virtual函數

發現很多朋友對於C#中的Abstract和Virtual函數區分得不是很清楚,下面我通過兩段代碼讓大家看看這兩者之間到底有什麼區別~~

開發環境: VS.net 2005

使用方法: 用以下代碼覆蓋program.cs中的代碼,然後run即可

第一段代碼: Abstract的用法

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

namespace ConsoleApplication3
{
    public abstract class Book
    {
        //抽象方法，不含主體，抽象方法所在類必須為抽象類別，衍生類別必須實現該方法
        public abstract void Introduce();
    }

    public interface iBook
    {
    }

    public class JavaBook : Book
    {
        //實現抽象方法，必須實現，必須添加override關鍵字
        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();      //將調用JavaBook中Introduce()
            Book book = new JavaBook();
            book.Introduce();      //將調用JavaBook中Introduce()
        }
        public static void Main()
        {
            test t = new test();
        }
    }
}

第二段代碼: 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，此方法沒有override父類的方法
        public void SayHi()
        {
            Console.WriteLine("Hi, I'm Java");
        }
    }

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

            javaBook.SayHi();      //將調用JavaBook中SayHi()
            book.SayHi();           //將調用Book中SayHi()
        }

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

 

第三段代碼: 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
    {
        // 沒有加new，但C#預設行為會加上new
        public void Introduce()
        {
            Console.WriteLine("I'm Java");
        }

        // 顯式加上new，跟不加new實際效果一樣，只是加new之後會消除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();       //將調用JavaBook中Introduce()
            javaBook.SayHi();           //將調用JavaBook中SayHi()
           
            book.Introduce();       //將調用Book中Introduce()
            book.SayHi();           //將調用Book中SayHi()
        }
        public static void Main()
        {
            test t = new test();
        }
    }
}