New a object ?

[ad]

I think we always new a class like below:ClassName 1 OjbectName=new
ClassName1();Bu t I find some example codes which new a class with different
classClassName1 OjbectName=new ClassName2();Wh at is the purpose to do so?

[Edward Diener]

The purpose is polymorphism. In OOP you can have a base class object
variable hold the addresses of derived class objects, and treat the object
polymorphically by calling virtual functions on the base class object
variable.

"ad" <[e-mail] u.tw> wrote in message
news:OY******** *****@TK2MSFTNG P12.phx.gbl...

I think we always new a class like below:ClassName 1 OjbectName=new
ClassName1();Bu t I find some example codes which new a class with
different
classClassName1 OjbectName=new ClassName2();Wh at is the purpose to do so?

[Morten Wennevik]

Hi ad,

Like Edward said a parent class or implemented interface can reference an
object.

class Parent
class Child : Parent

Parent p = new Child();

This is the same as
Child c = new Child();
Parent p = c;

p is just a reference to an object. All that is required of the p object
is that it can do everything
a Parent object can. This is very handy when you have methods that need
to handle different classes with a common parent or interface.

class FireMan : Human
class PoliceMan : Human

....
DoStuffToHuman( new FireMan())
....

void DoStuffToHuman( Human h)
{
}

--
Happy Coding!
Morten Wennevik [C# MVP]