Which Is the Object Here?

  • Thread starter Thread starter rn5a
  • Start date Start date
R

rn5a

Consider the following code:

-------------------------------------------
Class MyInt
Public MyValue As Integer
End Class

Sub Page_Load(..........)
Dim x As New MyInt
Dim y As New MyInt

x.MyValue = 15
y = x

y.MyValue = 30
Response.Write(x.MyValue)
End Sub
-------------------------------------------

Please note the line

x.MyValue = 15

This line assigns a value to the object but which is the object here -
MyValue, MyInt or x or x.MyValue?

Thanks,

Ron
 
Consider the following code:

-------------------------------------------
Class MyInt
Public MyValue As Integer
End Class

Sub Page_Load(..........)
Dim x As New MyInt
Dim y As New MyInt

x.MyValue = 15
y = x

y.MyValue = 30
Response.Write(x.MyValue)
End Sub
-------------------------------------------

Please note the line

x.MyValue = 15

This line assigns a value to the object but which is the object here -
MyValue, MyInt or x or x.MyValue?

Thanks,

Ron
Click to expand...

ADDENDUM:
==========

Also please note the line

Dim x As New MyInt

If I am not wrong, the above line creates space for "x" (allocates a
memory location to "x") & returns a pointer. To whom does it return
the pointer?
 
ADDENDUM:
==========

Also please note the line

Dim x As New MyInt

If I am not wrong, the above line creates space for "x" (allocates a
memory location to "x") & returns a pointer. To whom does it return
the pointer?- Hide quoted text -

- Show quoted text -
Click to expand...

Hai Ron

According to my knowledge, for your first question, I think
x.myvalue is an object.

Because in .NET everything is an object.

For the second question you are using "New" keyword, so it
creates an instance of the myInt class and returns the reference to x.

If it is wrong, then please explain.

Regards,
Raj
 
MyInt is a class, x is an object, x.MyValue is an integer.

Basically an object is a pointer. More precisely the New keyword allocates
space for an object instance of the MyInt class. The location of this space
is then returned to the x variable. From a programmer's point of view x is
the object (see this as a "symbol" that represents the object), technically
x is a pointer that points to the object.

http://msdn2.microsoft.com/en-us/library/b86b82w0(VS.80).aspx could help
(Object-Oriented Programming in Visual Basic).
 
MyInt is a class, x is an object, x.MyValue is an integer.

Basically an object is a pointer. More precisely the New keyword allocates
space for an object instance of the MyInt class. The location of this space
is then returned to the x variable. From a programmer's point of view x is
the object (see this as a "symbol" that represents the object), technically
x is a pointer that points to the object.

http://msdn2.microsoft.com/en-us/library/b86b82w0(VS.80).aspxcould help
(Object-Oriented Programming in Visual Basic).

--
Patrice

<[email protected]> a écrit dans le message de (e-mail address removed)...










- Show quoted text -
Click to expand...

Hai Ron,

Thank you!!!
 
MyInt is a class, x is an object, x.MyValue is an integer.

Basically an object is a pointer. More precisely the New keyword allocates
space for an object instance of the MyInt class. The location of this space
is then returned to the x variable. From a programmer's point of view x is
the object (see this as a "symbol" that represents the object), technically
x is a pointer that points to the object.

http://msdn2.microsoft.com/en-us/library/b86b82w0(VS.80).aspxcould help
(Object-Oriented Programming in Visual Basic).

--
Patrice

<[email protected]> a écrit dans le message de (e-mail address removed)...










- Show quoted text -
Click to expand...

Patrice, you have said that "More precisely the New keyword allocates
space for an object instance of the MyInt class" Do you mean to say
that the New keyword allocates space for the object "x"?

You have also said that "the location of this space is then returned
to the x variable". You have also said that "x" is the object. Now
since the location of this space is returned to the variable "x", is
"x" a pointer or is it the object or is it both?

Getting confused....

Thanks,

Ron
 
its easiier to see if broken up

dim x as MyInt 'declare and allocatate a MyInt object pointer (on the stack)

x = new MyInt 'allocate a new MyInt object in the heap and assign
location to pointer

x.MyValue = 15 'copy an integer value to integer value


the trick here is integers are valuetypes not objects. instead of a
pointer to an integer, MyValue as space allocated in the objects memory
to store the integer.

now when passing an integer to a method, it be be passed by value, the
parameter is the actual value, or passed by ref, the parameter is
pointer to integers memory location.

-- bruce (sqlwork.com)
 
..net has two major classes of memory objects (there are more but lets
keep it simple).

the first is a ValueType. ValueTypes are primitive datatypes like ints,
floats, datetime, enum, etc. ValueType have their storage directly
allocated because the size is know. also they can not be set to null.
ValueTypes can be copied, and passed as parameters to a method.

the second is objects, actually class instances. these are allocated in
the heap and managed by the GC. They can not be copied. Memory for a
class instance is create by the new operator.

variables are always valuestypes. if the variable is defined as a
valuetype, then it represents the value. if the variable is defined as
an object, then its a valuetype of object pointer.

if an object variable points to a valuetype, the valuetype is boxed (an
object wrapper is automatically created) and the variable points to the
object wrapper instance.

some examples:

myClass y = new myClass();
myClass x = y;

y points to new myClass instance allocated by the new operator. x
point's to the same class instance because it got a copy of y.

int y = 1;
int x = y;

y is valuetype of int, and integer value 1 is copied to it. the value of
y is copied to x.



-- bruce (sqlwork.com)
 
Back
Top