虚方法,抽象类,多态性
Code1. 虚方法必须有实现部分，抽象方法没有提供实现部分，抽象方法是一种强制派生类覆盖的方法，否则派生类将不能被实例化。如：
//抽象方法
public abstract class Animal
{
public abstract void Sleep();
public abstract void Eat();
}
//虚方法
public class Animal
{
public virtual void Sleep(){}
public virtual void Eat(){}
}
2. 抽象方法只能在抽象类中声明，虚方法不是。其实如果类包含抽象方法，那么该类也是抽象的，也必须声明为抽象的。如：
public class Animal
{
public abstract void Sleep();
public abstract void Eat();
}
编译器会报错：
Main.cs(10): 'VSTest.Animal.Sleep()' is abstract but it is contained in nonabstract class 'VSTest.Animal'
Main.cs(11): 'VSTest.Animal.Eat()' is abstract but it is contained in nonabstract class 'VSTest.Animal'
3. 抽象方法必须在派生类中重写,这一点跟接口类似，虚方法不必。如果一个类派生自抽象类但没有完全实现所有抽象方法,那么这个类本身也必须声明为抽
象的.另外抽象类不能实例化,但可以定义抽象类的引用,这种引用能够指向派生自该抽象类的非抽象子类的实例,调用这些虚拟和抽象方法时将自动按照多态性
执行.抽象方法不能具有私有可见性,否则派生类将无法实现它.抽象类可以有构造函数,字段,属性如：
public abstract class Animal
{
public abstract void Sleep();
public abstract void Eat();
}
public class Cat : Animal
{
public override void Sleep()
{
Console.WriteLine( "Cat is sleeping" );
}
// we need implement Animal.Eat() here
}
编译器会报错：Main.cs(14): 'VSTest.Cat' does not implement inherited abstract member 'VSTest.Animal.Eat()'，因为我们没有实现抽象类中所有抽
象方法。
多态性实例:
using System;
using System.Collections.Generic;
using System.Text;
namespace AbstractApplication
{
public class Employee
{
protected string m_Name;
public Employee(string name)
{
m_Name = name;
}
public virtual void Display()
{
System .Console.WriteLine("Name:{0}", m_Name );
}
}
class Secretary : Employee
{
public Secretary(string name) : base(name) { }
public override void Display()
{
base.Display();
System.Console.WriteLine("Excute: Sectretary\n");
}
}
class Technician : Employee
{
public Technician(string name) : base(name) { }
public override void Display()
{
base.Display();
System.Console.WriteLine("Excute:Technician\n");
}
}
class Manager : Employee
{
public Manager(string name) : base(name) { }
public new void Display()//屏蔽多态性
{
base.Display();
System.Console.WriteLine("Excute:Technician\n");
}
}
class AbstractApp
{
static void Main(string[] args)
{
Console.WriteLine("---------多态性------------");
Employee[] array = new Employee[4];
array[0] = new Technician("carl");
array[1] = new Secretary("hubcarl");
array[2] = new Secretary("anan");
array[3] = new Employee("Employee");
foreach (Employee employee in array)
{
employee.Display();
}
Console.WriteLine("---------屏蔽多态性------------");
Employee[] array1 = new Employee[4];
array1[0] = new Manager("carl");//调用的是基类的Display方法
array1[1] = new Secretary("hubcarl");
array1[2] = new Secretary("anan");
array1[3] = new Employee("Employee");
foreach (Employee employee in array1)
{
employee.Display();
}
//((Manager)array[0]).Display();
}
}
}
运行结果:
