Casting object

Matglas

I was trying to "upper" cast a class. I looked like this but I get a Exception. Is there anyway to have a extended class and cast to it?

public class FirstClass {

}

public class SecondClass : FirstClass {

}

public class Main {

  public Main() 
  {
    FirstClass iFirstC = new FirstClass();
    SecondClass iSecondC = (SecondClass)iFirstC;
  }
}

I get a error on the line.

SecondClass iSecondC = (SecondClass)iFirstC;

Ravi Bhavnani

While syntactically correct, executing that statement will throw an exception, since an instance of iFirstC is not of type SecondClass. If you prefer not to handle exceptions, you should use the as operator and check for null.

SecondClass iSecondC = iFirstC as SecondClass;
if (iSecondC == null) {
// Handle error
}

/ravi

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Lost User

You can only cast SecondClass to FirstClass, but not FirstClass to SecondClass. FirstClass is parent, SecondClass is child.

Colin Angus Mackay

Matglas wrote:

Is there anyway to have a extended class and cast to it?

Only if the object is of the "extended class" (aka derived class). The following will work:

FirstClass iFirstC = new SecondClass();
SecondClass iSecondC = (SecondClass)iFirstC;

This is because the actual object is a SecondClass even although it is initially referenced as a FirstClass. Does this help?

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Matglas

Thanks all for the great input. I start to understand it better now. So it does help.