Distinction between abstract classes and virtual methods

Abstract class defines:
while its function is to generate the subclass specific properties and to a subclass.
abstract modifier classes can be used with the methods, properties, events, and indexers. Use the abstract modifier in a class declaration to indicate that a class is the only other class of the parent class. Contained in the abstract or abstract class members must be achieved from the subclass of abstract class mark.

Characteristics:
1. An abstract class that can not be instantiated;
2. abstract class may contain abstract methods and accessors;
3. not modified with the sealed modifier;
4 derived from the abstract class must include non-abstract class inherits all abstract methods and implement the abstract accessor.

Summary:
~ abstract method is implicit virtual method;
~ only allow the use of abstract classes in the abstract method declarations;
~ as an abstract method declaration provides actual implementation, there is no method body; method declaration simply ends with a semicolon, and after the signature without braces "{}", implemented by a method override, override this method is non-members of the abstract class;
~ or use static virtual modifier in the abstract method declaration is wrong;
~ in addition to the statement and call syntax different, the behavior of abstract properties and methods as abstract;
~ use the abstract modifier on a static property is wrong;

~ In a derived class, by using override modifier including property declarations, can override inherited attributes abstract. Abstract class defines:
while its function is to generate the subclass specific properties and to a subclass.
abstract modifier classes can be used with the methods, properties, events, and indexers. Use the abstract modifier in a class declaration to indicate that a class is the only other class of the parent class. Contained in the abstract or abstract class members must be achieved from the subclass of abstract class mark.

using System;
abstract class A
{
    public abstract void F();
    protected int _x;
    public abstract int X
    {
        get;
        set;
    }
}
class B:A
{
    public override void F()
    {
        
    }
    public override int X
    {
        get{return _x;}
        set{_x=value;}
    }
}
class Test
{
    static void Main()
    {
        B b=new B();
        b.X=10;
        Console.Write(b.X);
    }
}

 

Virtual methods defined:
Briefly, the method can be subclassed virtual method is overridden, if subclass overrides a virtual method, then uses the logical overwrite operation when the, if not rewritten, using the parent class virtual logic method;
Virtual keys for modification methods, properties, or events indexer declarations and allows rewriting these objects in a derived class.

using   System   ;  
   
  class   A  
   
  {  
   
  public   void   F(   )  
  {   
      Console.WriteLine("A.F")   ;  
  }
   
  public   virtual   void   G(   )  
  {  
      Console.WriteLine("A.G")   ;   
  }
   
  }  
   
  class   B:   A  
   
  {  
   
  new   public   void   F(   )  
  {   
      Console.WriteLine("B.F")   ;  
  }
   
  public   override   void   G(   )  
  {   
      Console.WriteLine("B.G")   ; 
  }
   
  }  
   
  class   Test  
   
  {  
   
  static   void   Main(   )    
   
  {  
  B   b   =   new   B(   )   ;  
   
  A   a   =   b;  
   
  a.F(   )   ;  
   
  b.F(   )   ;  
   
  a.G(   )   ;  
   
  b.G(   )   ;  
   
  }  
   
  }   输出是：A.F   B.F  B.G  B.G

Actually, the most important thing is an abstract method can not be instantiated, subclass must be mandatory cover its methods. And virtual methods is to provide a choice, may not cover may cover, inherited virtual method in the base class.

Compare summarized as follows:

The difference between abstract methods and virtual methods:

 - the difference between abstract methods and virtual methods are: virtual method has an implementation section, and provides the option to override this method in a derived class, on the contrary, an abstract method does not provide an implementation part, to force derived classes covering methods (or a derived class can not be specific type); ~
abstract method declarations in an abstract class only, not the virtual method;
~ abstract methods must be overridden in a derived class, and it is not necessary virtual;
~ method can not abstract method declarations entity may be a virtual method.