C#中繼承與函數(shù)覆蓋，有時(shí)比較復(fù)雜，不小心很容易弄錯(cuò)。所以有必要總結(jié)點(diǎn)規(guī)律出來(lái)。
(1)
當(dāng)子類(lèi)中擁有和父類(lèi)一樣的可見(jiàn)field和member function時(shí)，子類(lèi)中的field和member function會(huì)覆蓋父類(lèi)中的定義。
using System;
namespace TestInheritance
{
public class Bird
{
public string type = "Bird";
public void ShowType()
{
Console.WriteLine("Type is {0}", type);
}
}
public class Chicken : Bird
{
//同名的field，可見(jiàn)性為public或者protected，不管有沒(méi)有聲明為new，均會(huì)覆蓋父類(lèi)中的field
public new string type = "Chicken";
//當(dāng)子類(lèi)含有和父類(lèi)相同的函數(shù)簽名（可見(jiàn)性public或者protected、函數(shù)名和參數(shù)都相同）時(shí)，不管帶new與否，都將覆蓋父類(lèi)中相同的函數(shù)
public /**//*new*/ void ShowType()
{ Console.WriteLine();
Console.WriteLine("This is Chicken::ShowType()", type);
}
}
public class TestInheritance
{
public static void Main()
{
Bird bird = new Chicken();
bird.ShowType();
Console.WriteLine();
Chicken chicken = new Chicken();
chicken.ShowType();
Console.WriteLine();
Console.WriteLine("Type is {0}", chicken.type);
Console.Read();
}
}
}
如上例中的輸出會(huì)是：
Type is Bird
This is Chicken::ShowType()
Type is Chicken
(2) 當(dāng)子類(lèi)中的member function 和field作用范圍比父類(lèi)中對(duì)應(yīng)的member function和field小時(shí)，只會(huì)對(duì)作用范圍內(nèi)的部分產(chǎn)生覆蓋影響，對(duì)作用范圍外無(wú)影響。
如下例：
using System;
namespace TestInheritance
{
public class Bird
{
public string type = "Bird";
public void ShowType()
{
Console.WriteLine("Type is {0}", type);
}
}
public class Chicken : Bird
{
//這里的type只會(huì)對(duì)Chicken內(nèi)部的函數(shù)有影響，出了Chicken類(lèi)，該函數(shù)不具有作用。
private new string type = "Chicken";
//這里的ShowType()函數(shù)只會(huì)對(duì)Chicken內(nèi)部的函數(shù)有影響，出了Chicken類(lèi)，該函數(shù)不具有作用。
private /**//*new*/ void ShowType()
{
Console.WriteLine("This is Chicken::ShowType()", type);
}
public void ShowInfo()
{
ShowType();
}
}
public class TestInheritance
{
public static void Main()
{
Bird bird = new Chicken();
bird.ShowType();
Console.WriteLine();
Chicken chicken = new Chicken();
chicken.ShowType();
Console.WriteLine();
Console.WriteLine("Type is {0}", chicken.type);
Console.WriteLine();
chicken.ShowInfo();
Console.Read();
}
}
}
輸出：
Type is Bird
This is Bird
Type is Bird
This is Chicken::ShowType()
又如下例：
using System;
namespace TestInheritance
{
public class Bird
{
public string type = "Bird";
public void ShowType()
{
Console.WriteLine("Type is {0}", type);
}
}
public class Chicken : Bird
{
//這里的type只會(huì)對(duì)Chicken內(nèi)部的函數(shù)有影響，出了Chicken類(lèi)，該函數(shù)不具有作用。
protected new string type = "Chicken";
//這里的ShowType()函數(shù)只會(huì)對(duì)Chicken內(nèi)部的函數(shù)有影響，出了Chicken類(lèi)，該函數(shù)不具有作用。
protected /**//*new*/ void ShowType()
{
Console.WriteLine("This is Chicken::ShowType()", type);
}
public void ShowInfo()
{
ShowType();
}
}
public class Cock : Chicken
{
public void ShowInfo()
{
Console.WriteLine("Cock::ShowInfo()");
//這里會(huì)調(diào)用Chicken的type成員
Console.WriteLine(type);
//這里將調(diào)用Chicken的ShowType()函數(shù)
ShowType();
}
}
public class TestInheritance
{
public static void Main()
{
Bird bird = new Chicken();
//調(diào)用Bird的ShowType()函數(shù)
bird.ShowType();
Console.WriteLine();
Chicken chicken = new Chicken();
//這里會(huì)調(diào)用Bird的ShowType();
chicken.ShowType();
//這里chicken.type會(huì)為Bird，因?yàn)镃hicken類(lèi)中type為protected，在這里沒(méi)法訪問(wèn)
Console.WriteLine("Type is {0}", chicken.type);
chicken.ShowInfo();
Console.WriteLine();
Cock cock = new Cock();
cock.ShowInfo();
Console.Read();
}
}
}
會(huì)輸出：
Type is Bird
Type is Bird
Type is Bird
This is Chicken::ShowType()
Cock::ShowInfo()
Chicken
This is Chicken::ShowType()
(3) 當(dāng)子類(lèi)中的member function 和父類(lèi)的member function名字相同但參數(shù)不同時(shí)，不會(huì)產(chǎn)生覆蓋。如：
using System;
namespace TestInheritance
{
public class Bird
{
public string type = "Bird";
public void ShowType()
{
Console.WriteLine("Type is {0}", type);
}
}
public class Chicken : Bird
{
//這里的type只會(huì)對(duì)Chicken內(nèi)部的函數(shù)有影響，出了Chicken類(lèi)，該函數(shù)不具有作用。
protected new string type = "Chicken";
//不會(huì)覆蓋Bird的ShowType函數(shù)，因?yàn)楹瘮?shù)簽名不同（參數(shù)不同）
public /**//*new*/ void ShowType(int x)
{
Console.WriteLine("int {0}",x);
Console.WriteLine("This is Chicken::ShowType()", type);
}
public void ShowInfo()
{
//會(huì)調(diào)用Bird的ShowType函數(shù)
Console.WriteLine();
Console.WriteLine("Chicken::ShowInfo()");
ShowType();
}
}
public class Cock : Chicken
{
public void ShowInfo()
{
Console.WriteLine();
Console.WriteLine("Cock::ShowInfo()");
//這里會(huì)調(diào)用Chicken的type成員
Console.WriteLine(type);
//這里將調(diào)用Bird的ShowType()函數(shù)
ShowType();
}
}
public class TestInheritance
{
public static void Main()
{
Bird bird = new Chicken();
//調(diào)用Bird的ShowType()函數(shù)
bird.ShowType();
Chicken chicken = new Chicken();
//這里會(huì)調(diào)用Bird的ShowType();
chicken.ShowType();
//這里chicken.type會(huì)為Bird，因?yàn)镃hicken類(lèi)中type為protected，在這里沒(méi)法訪問(wèn)
Console.WriteLine("Type is {0}", chicken.type);
chicken.ShowInfo();
Cock cock = new Cock();
cock.ShowInfo();
Console.Read();
}
}
}
輸出為：
Type is Bird
This is Bird
Type is Bird
Chicken::ShowInfo()
Type is Bird
Cock::ShowInfo()
Chicken
Type is Bird。
這里沒(méi)有列舉虛函數(shù)和override，考慮到篇幅，那個(gè)將在其它文章中予以說(shuō)明，相信通過(guò)以上幾個(gè)實(shí)例，大家可以對(duì)函數(shù)覆蓋有個(gè)比較好的了解。