Type Casting

Question

Hi ... I have one doubt in casting

BaseClass bc = dc; //1

BaseClass bc1 = (BaseClass)dc; //2

BaseClass bc2 = new Derived(); //3

BaseClass bc3= dc as BaseClass; //4

these 4 lines produce same o/p. but what is difference in this?
which one is better ?

My simple code is here,

using System;
using System.Collections.Generic;
using System.Text;

namespace Example
{
class BaseClass
{
public void Method()
{
Console.WriteLine("This is Base Class");
}
}

class Derived: BaseClass
{
new public void Method()
{
Console.WriteLine("This is Derived Class");

}
}

class Program
{
static void Main(string[] args)
{
Derived dc = new Derived();

BaseClass bc = dc; //1

BaseClass bc1 = (BaseClass)dc; //2

BaseClass bc2 = new Derived(); //3

BaseClass bc3= dc as BaseClass; //4

dc.Method();
bc.Method();
bc1.Method();
bc2.Method();
bc3.Method();
}
}
}

O/P

This is Derived Class
This is Base Class
This is Base Class
This is Base Class
This is Base Class

plz help me.. anybody

Prakash K · Answer

thank u...

Sam Hobbs · Answer

It is a matter of the purpose. Number 4 is the only choice if there is any possibility that the object cannot be cast which often is a problem and there are no other ways that errors are caught gracefully. Beginners reading this should not ignore the possibility for errors. If the developer can be assured that the cast will work then perhaps it is appropriate to assume it will. Also note that the alternatives to the as operator are acceptable if there are try/catch blocks or some other way to catch errors gracefully.

Vulpes · Answer

1 and 3 are better than 2 or 4 because they don't involve any unnecessary casts - a derived class is always implicitly convertible to its base class. If you don't need to use the Derived variable 'dc' anywhere else in the method then 3 is better than 1 because it is only necessary to allocate one local variable on the call stack. However in this example you are using 'dc' to call Method().