A question about method overriding in c#

class xxx
{
   public virtual void function1()
   {
     // Some code here
   }
}

class  yyy : xxx
{
   public override void function1()
   {
    // some code here
   }
}

class result
{
   public result(){}

   // In the main i write as

   xxx x开发者_运维百科obj = new yyy();
   xobj.function1(); // by calling this function1 in yyy will invoked

   yyy yobj = new xxx();
   yobj.function1()     // which function will be called here
}

ple

Well, first of all:

yyy yobj = new xxx();
yobj.function1();

will cause a compile error. yyy is a xxx, but xxx is not a yyy.

Secondly:

xxx xobj = new yyy();
xobj.function1();

will cause function1() of class xxx to be executed because the variable is of type xxx. to call the method on class yyy you will need to cast the variable to type yyy

xxx xobj = new yyy();
((yyy)xobj).function1();

This is a classic common misconception about inheritance. Inheritance is not bidirectional. By this I mean that a sub class is a type of a super class .. but it is not true the other way around.

public class Base
{
}

public class Sub : Base
{
}


Base baseObj = new Base(); //this is just fine
Base subAsBase = new Sub(); //this is just fine, a Sub is a type of Base

Sub subAsBase = new Base(); //this will spit a compile error. A Base is NOT a type of Sub, it is the other way around.

Likewise, I could perform the following casting:

Base baseObj = null;
Sub subObj = new Sub();
baseObj = subObj; //now I am storing a sub instance object in a variable declared as Base

Sub castedSubObj = baseObj as Sub; //simply casted it back to it's concrete type

You cannot cast xxx to yyy, so yyy yobj = new xxx(); won't compile