Chapter 5 Pages 182 to 183 Constructors

epc · October 2nd, 2009, 01:51 PM

Two part question:

1. When I created a C# class file in the App_Code folder I was able to see this code within the file which includes the default constructor.

Public class ClassName
{
Public ClassName()
{

}
}

When I created a similar class file for VB I did not see anything that looked like
the code on page 182 listed below.

Public Class Class Name
Public Sub New()

End Sub
End Class

Book states the VB constructor will be created by the compliler. Can I see this somewhere in code?

2. Why does the VB code use Sub before the constructor

Public Sub New()

but void is not used before the c# constructor code? Seems like the vb code is creating a subroutine.

Any thoughts would be helpful. Thanks!

Imar · October 2nd, 2009, 02:39 PM

Hi there,

Quote from the book:

Quote:

By default, when you create a new class in Visual Web Developer, you get a default constructor for C# but not for VB.NET.

This is purely a template issue. That is, in C#, the constructor is added, in VB.NET it isn't. The code on page 182 is to show how a default constructor looks but doesn't reflect the New Class template.

This means that in VB.NET, the following are functionally the same:

Code:

' Without constructor
Public Class PersonEnd Class
 
' With constructor
Public Class Person
  Public Sub New()
  End Sub
End Class

In C#, this is the same:

Code:

 
// Without constructor
public class Person
{}
 
// With constructor
public class Person
{
 public Person()
 {
 }
}

So, the difference between the two is purely the default code that is added by the Class template.

Quote:

Book states the VB constructor will be created by the compliler. Can I see this somewhere in code?

Not directly, But you can see it when instantiating a class without an explicit constucor works. E.g.:

Code:

' Without constructor
Public Class PersonEnd Class
 
Public Class SomeOtherClass
Public Sub SomeMethod
  Dim myPerson As New Person() ' works because of the default constructor.
End Sub
End Class

Quote:

Seems like the vb code is creating a subroutine.

Yes, but because it uses the reserved New keyword, the compiler knows you're defining a constructor. It's probably a better question for the C# and VB.NET compiler teams, but my guess is that the grammar for VB.NET somehow requires the Sub word, while C# doesn't....

Hope this clarifies things.

Imar