摘要：繼承和多態(tài)*繼承可以讓class具有一種特殊的能力，即實現(xiàn)class本身定義的所有功能外，還可以對父類（或稱為基類、超類）的某些屬性和功能進行擴展，這樣的類我們稱之為子類（或派生類）。繼承有如下的幾個規(guī)則：1. 可傳遞性：如： C是B的子類，B是A的子類，那么C會同時繼承B和A；（object為所有類的基類）2. 唯擴展性：子類應是對父類的擴展，而不能在子類除去父類里面的定義；3. 構(gòu)造函數(shù)和析構(gòu)
繼承和多態(tài)
*繼承可以讓class具有一種特殊的能力，即實現(xiàn)class本身定義的所有功能外，還可以對父類（或稱為基類、超類）的某些屬性和功能進行擴展，這樣的類我們稱之為子類（或派生類）。
繼承有如下的幾個規(guī)則：
1. 可傳遞性：
如： C是B的子類，B是A的子類，那么C會同時繼承B和A；（object為所有類的基類）
2. 唯擴展性：
子類應是對父類的擴展，而不能在子類除去父類里面的定義；
3. 構(gòu)造函數(shù)和析構(gòu)函數(shù)不能被繼承：
除去構(gòu)造函數(shù)和析構(gòu)函數(shù)不能被繼承，其他的成員都能被繼承（注意區(qū)別：能被繼承和能被訪問，是兩個概念）
4. 重載屏蔽性：
如果子類定義了和父類成員同名的新成員，那么會執(zhí)行重載和覆蓋邏輯。但要明白的是，這樣做，并不是刪除了父類的這些成員，而是不能再訪問這些被重載和覆蓋的成員而已。
5. 子類可以從父類的虛方法、虛屬性以及虛索引器進行重載（即多態(tài)）
我們可以借用override關(guān)鍵字對父類的虛方法、虛屬性以及虛索引器進行重載；
同時，我們也可以借用override關(guān)鍵字對抽象父類的抽象方法進行重載。
abstract和virtural的區(qū)別：
（1） abstract可以修飾class以及abstract class內(nèi)部的函數(shù)、屬性和索引器；而virtual不可以修飾class；
?。?） abstract修飾內(nèi)部的函數(shù)、屬性和索引器的時候，必須在abstract class才可以；而且abstract函數(shù)、屬性和索引器不可以在abstract class里面有實現(xiàn)，但virtual必須要有實現(xiàn)。
?。?） virtual既可以修飾abstract class里面的函數(shù)、屬性和索引器，也可以修飾一般class里面的函數(shù)、屬性和索引器；
*基礎知識擴展：什么是索引器？
索引器允許類或者結(jié)構(gòu)的實例按照與數(shù)組相同的方式進行索引取值，索引器與屬性類似，不同的是索引器的訪問是帶參的。
A. 索引器和數(shù)組比較：
(1)索引器的索引值(Index)類型不受限制；
(2)索引器允許重載；
(3)索引器不是一個變量；
B. 索引器和屬性的不同點
(1)屬性以名稱來標識，索引器以函數(shù)形式標識；
(2)索引器可以被重載，屬性不可以；
(3)索引器不能聲明為static，屬性可以；
下面一個簡單的例子可見一斑：
public class MyClass
{
private string[] _strArray;
public MyClass(int length)
{
this._strArray = new string[length];
}
public string this[int index]
{
get
{
if (index < this._strArray.Length)
{
return this._strArray[index];
}
return null;
}
set
{
if (index < this._strArray.Length)
{
this._strArray[index] = value;
}
}
}
}static void Main(string[] args)
{
MyClass myClass = new MyClass(3);
myClass[0] = "A";
myClass[1] = "B";
myClass[2] = "C";
Console.WriteLine(myClass[0]);
Console.WriteLine(myClass[1]);
Console.WriteLine(myClass[2]);
Console.ReadLine();
}運行結(jié)果：
A
B
C
6. 子類只能繼承一個父類（class），而可以繼承多個接口（interface）（多重繼承）
*多態(tài)性：同一操作作用于不同的類的實例，將產(chǎn)生不同的執(zhí)行結(jié)果，即不同類的對象收到相同的消息時，得到不同的結(jié)果。
下圖所示的類之間繼承關(guān)系和多態(tài)用法，可以讓大家更好了解這些概念的意義：
具體的實現(xiàn)代碼：
public abstract class Creature
{
private string _spiece;
public Creature(string spiece)
{
this._spiece = spiece;
}
public string Spiece
{
get { return this._spiece; }
}
public abstract void Breath();
}public class Animal : Creature
{
private bool? _sex;
public Animal(string spiece)
: base(spiece)
{
this._sex = null;
}
public bool? Sex
{
get { return _sex; }
}
public virtual void Run()
{
Console.WriteLine("I am running...");
}
public override void Breath()
{
Console.WriteLine("I am breathing by animal respiration...");
}
}public class Monkey : Animal
{
public Monkey(string spiece)
: base(spiece) { }
public void ClimbTree()
{
Console.WriteLine("I am climbing tree...");
}
public override void Run()
{
Console.WriteLine("I am running with two legs, sometimes with four legs...");
}
public override void Breath()
{
Console.WriteLine("I am breathing with lung...");
}
}public class Fish : Animal
{
public Fish(string spiece)
: base(spiece) { }
public override void Run()
{
Console.WriteLine("I am running in the water with fins...");
}
public override void Breath()
{
Console.WriteLine("I am breathing with cheek...");
}
}public class Plant : Creature
{
public Plant(string spiece)
: base(spiece) { }
public override void Breath()
{
Console.WriteLine("I am breathing by plant respiration...");
}
}public class Tree : Plant
{
public Tree(string spiece)
: base(spiece) { }
//重載Breath()內(nèi)部調(diào)用base.Breath()，其實和不寫沒啥區(qū)別，這里只是想告訴大家本質(zhì)是什么。
public override void Breath()
{
base.Breath();
}
}程序運行測試代碼：
class Program
{
static void Main(string[] args)
{
Creature creature001 = new Animal("Animal");
Console.WriteLine(creature001.Spiece);
creature001.Breath();
Console.WriteLine("—————————————————————————");
Creature creature002 = new Plant("Plant");
Console.WriteLine(creature002.Spiece);
creature002.Breath();
Console.WriteLine("—————————————————————————");
Animal animal001 = new Animal("Animal", true);
Console.WriteLine(animal001.Spiece);
Console.WriteLine(string.Format("Spiece:{0}; Sex:{1}", animal001.Spiece, GetSexName(animal001.Sex)));
animal001.Breath();
animal001.Run();
Console.WriteLine("—————————————————————————");
Creature monkey001 = new Monkey("Monkey", true);
Console.WriteLine(monkey001.Spiece);
monkey001.Breath();
Console.WriteLine("—————————————————————————");
Animal animal002 = new Monkey("Monkey", false);
Console.WriteLine(animal002.Spiece);
Console.WriteLine(string.Format("Spiece:{0}; Sex:{1}", animal002.Spiece, GetSexName(animal002.Sex)));
animal002.Breath();
animal002.Run();
Console.WriteLine("—————————————————————————");
Creature fish001 = new Fish("Fish", true);
Console.WriteLine(fish001.Spiece);
monkey001.Breath();
Console.WriteLine("—————————————————————————");
Animal fish002 = new Fish("Fish", true);
Console.WriteLine(fish001.Spiece);
Console.WriteLine(string.Format("Spiece:{0}; Sex:{1}", fish002.Spiece, GetSexName(fish002.Sex)));
fish002.Breath();
fish002.Run();
Console.WriteLine("—————————————————————————");
Animal animal004 = new Monkey("Monkey", false);
Console.WriteLine(animal004.Spiece);
Console.WriteLine(string.Format("Spiece:{0}; Sex:{1}", animal004.Spiece, GetSexName(animal004.Sex)));
animal002.Breath();
animal002.Run();
Console.WriteLine("—————————————————————————");
Monkey jack = new Monkey("Monkey", true);
Console.WriteLine(jack.Spiece);
Console.WriteLine(string.Format("Spiece:{0}; Sex:{1}", jack.Spiece, GetSexName(jack.Sex)));
jack.Breath();
jack.Run();
jack.ClimbTree();
Console.ReadLine();
}
private static string GetSexName(bool? value)
{
string sexName = null;
if (value == null)
{
sexName = "undefined";
}
else
{
sexName = value.Value ? "male" : "female";
}
return sexName;
}
}運行結(jié)果：
Animal I am breathing by animal respiration... ————————————————————————— Plant I am breathing by plant respiration... ————————————————————————— Animal Spiece:Animal; Sex:male I am breathing by animal respiration... I am running... ————————————————————————— Monkey I am breathing with lung... ————————————————————————— Monkey Spiece:Monkey; Sex:female I am breathing with lung... I am running with two legs, sometimes with four legs... ————————————————————————— Fish I am breathing with lung... ————————————————————————— Fish Spiece:Fish; Sex:male I am breathing with cheek... I am running in the water with fins... ————————————————————————— Monkey Spiece:Monkey; Sex:female I am breathing with lung... I am running with two legs, sometimes with four legs... ————————————————————————— Monkey Spiece:Monkey; Sex:male I am breathing with lung... I am running with two legs, sometimes with four legs... I am climbing tree...
*多重繼承
類和接口都可以繼承接口，而且可以繼承不止一個接口。
需求：
IDraw接口，定義DrawLine、DrawCircle和DrawRectangle方法；
Drawer，定義為抽象類，實現(xiàn)IDraw接口，附加屬性Name；
ImpressionistDrawer（印象畫派畫家）類，繼承Drawer抽象類；
RealismDrawer（寫實主義畫派畫家）類，繼承Drawer抽象類。
如此，代碼如下：
public interface IDraw
{
void DrawLine();
void DrawCircle();
void DrawRectangle();
}public abstract class Drawer : IDraw
{
private string _name;
public Drawer(string name)
{
this._name = name;
}
public string Name
{
get
{
return this._name;
}
}
public abstract void DrawLine();
public abstract void DrawCircle();
public abstract void DrawRectangle();
}//印象畫派畫家
public class ImpressionistDrawer : Drawer
{
public ImpressionistDrawer(string name)
: base(name) { }
public override void DrawLine()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is drawing a line with pen.", this.Name));
}
public override void DrawCircle()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is drawing a circle with pen.", this.Name));
}
public override void DrawRectangle()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is drawing a rectangle with pen.", this.Name));
}
}//寫實主義畫派畫家
public class RealismDrawer : Drawer
{
public RealismDrawer(string name)
: base(name) { }
public override void DrawLine()
{
Console.WriteLine(string.Format("The realism drawer:{0} is drawing a line with pencil.", this.Name));
}
public override void DrawCircle()
{
Console.WriteLine(string.Format("The realism drawer:{0} is drawing a circle with pencil.", this.Name));
}
public override void DrawRectangle()
{
Console.WriteLine(string.Format("The realism drawer:{0} is drawing a rectangle with pencil.", this.Name));
}
}調(diào)用：
static void Main(string[] args)
{
IDraw draw001 = new RealismDrawer("莫柰");
draw001.DrawCircle();
draw001.DrawLine();
draw001.DrawRectangle();
Console.WriteLine();
IDraw draw002 = new ImpressionistDrawer("弗洛伊德");
draw002.DrawCircle();
draw002.DrawLine();
draw002.DrawRectangle();
Console.ReadLine();
}運行結(jié)果：
The realism drawer:莫柰 is drawing a circle with pencil.
The realism drawer:莫柰 is drawing a line with pencil.
The realism drawer:莫柰 is drawing a rectangle with pencil.
The impressionist drawer:弗洛伊德 is drawing a circle with pen.
The impressionist drawer:弗洛伊德 is drawing a line with pen.
The impressionist drawer:弗洛伊德 is drawing a rectangle with pen.
擴展一下，比方說：這些畫家除了要畫畫之外，一樣都要吃飯睡覺打豆豆，怎么處理呢？
我們當然不能把吃飯睡覺打豆豆歸為IDraw這個intercace里面，因為這完全是不相干的行為呀！于是，我們考慮新建一個interface
public interface ILive
{
void EatRice();
void Sleep();
void BeatDouDou();
}public abstract class Drawer : IDraw, ILive
{
private string _name;
public Drawer(string name)
{
this._name = name;
}
#region IDraw
public string Name
{
get
{
return this._name;
}
}
public abstract void DrawLine();
public abstract void DrawCircle();
public abstract void DrawRectangle();
#endregion
#region ILive
public abstract void EatRice();
public abstract void Sleep();
public abstract void BeatDouDou();
#endregion
}public ImpressionistDrawer(string name)
: base(name) { }
public override void DrawLine()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is drawing a line with pen.", this.Name));
}
public override void DrawCircle()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is drawing a circle with pen.", this.Name));
}
public override void DrawRectangle()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is drawing a rectangle with pen.", this.Name));
}
public override void EatRice()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is eating rice.", this.Name));
}
public override void Sleep()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is sleeping.", this.Name));
}
public override void BeatDouDou()
{
Console.WriteLine(string.Format("The impressionist drawer:{0} is beating DouDou.", this.Name));
}
}public class RealismDrawer : Drawer
{
public RealismDrawer(string name)
: base(name) { }
public override void DrawLine()
{
Console.WriteLine(string.Format("The realism drawer:{0} is drawing a line with pencil.", this.Name));
}
public override void DrawCircle()
{
Console.WriteLine(string.Format("The realism drawer:{0} is drawing a circle with pencil.", this.Name));
}
public override void DrawRectangle()
{
Console.WriteLine(string.Format("The realism drawer:{0} is drawing a rectangle with pencil.", this.Name));
}
public override void EatRice()
{
Console.WriteLine(string.Format("The realism drawer:{0} is eating rice.", this.Name));
}
public override void Sleep()
{
Console.WriteLine(string.Format("The realism drawer:{0} is sleeping.", this.Name));
}
public override void BeatDouDou()
{
Console.WriteLine(string.Format("The realism drawer:{0} is beating DouDou.", this.Name));
}
}調(diào)用：
static void Main(string[] args)
{
IDraw drawer001 = new RealismDrawer("莫柰");
drawer001.DrawCircle();
drawer001.DrawLine();
drawer001.DrawRectangle();
Console.WriteLine();
IDraw drawer002 = new ImpressionistDrawer("弗洛伊德");
drawer002.DrawCircle();
drawer002.DrawLine();
drawer002.DrawRectangle();
Console.WriteLine();
ILive drawer003 = new RealismDrawer("莫柰");
drawer003.EatRice();
drawer003.Sleep();
drawer003.BeatDouDou();
Console.WriteLine();
ILive drawer004 = new RealismDrawer("弗洛伊德");
drawer004.EatRice();
drawer004.Sleep();
drawer004.BeatDouDou();
Console.ReadLine();
}運行結(jié)果：
The realism drawer:莫柰 is drawing a circle with pencil. The realism drawer:莫柰 is drawing a line with pencil. The realism drawer:莫柰 is drawing a rectangle with pencil. The impressionist drawer:弗洛伊德 is drawing a circle with pen. The impressionist drawer:弗洛伊德 is drawing a line with pen. The impressionist drawer:弗洛伊德 is drawing a rectangle with pen. The realism drawer:莫柰 is eating rice. The realism drawer:莫柰 is sleeping. The realism drawer:莫柰 is beating DouDou. The realism drawer:弗洛伊德 is eating rice. The realism drawer:弗洛伊德 is sleeping. The realism drawer:弗洛伊德 is beating DouDou.