Static

13y1.3kVisual Basic .NET

Following one is a simple program. I inserted static key word to the object class variable idNumber. Program is compiling fine, but I expected an error message. Please explain me what is the reason for its compilation with or without key word static.

using System;
public class CreateEmployee
{
public static void Main()
{
Employee myAssistant = new Employee();

myAssistant.SetId(345); //Instance Method

Console.WriteLine("ID # is {0}", myAssistant.GetId());

Console.ReadKey();
}
}
internal class Employee
{
private static int idNumber;

public int GetId()
{
return idNumber;
}
public void SetId(int id)
{
idNumber = id;
}
}
//ID # is 345

6 Replies

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Vulpes13y ago
Accepted answer
A static field of a class is stored in a special area of the heap, and not within any particular instance of that class.

This is why there's only one copy for the class as a whole and why it knows nothing about any particular instances.

If idNumber were an instance field, then it would be stored within the memory set aside on the heap for each instance and consequently each instance would have its own copy.

So in your program the two instances, mAssistant1 and myAssistant2, are accessing the same memory location and this therefore returns the same value when GetId() is called successively on each instance.
13y ago
Thank you for your explanation.
13y ago
In this program even though we use static key word in the object class variable idNumber, computer memory location is different (one is myAssistant1 and other one is myAssistant2). Please tell me why output is a last value for both calls.

using System;
public class CreateEmployee
{
public static void Main()
{
Employee myAssistant1 = new Employee();

myAssistant1.SetId(345);

Employee myAssistant2 = new Employee();

myAssistant2.SetId(346);

Console.WriteLine("ID # is {0}", myAssistant1.GetId());
Console.WriteLine("ID # is {0}", myAssistant2.GetId());

Console.ReadKey();
}
}
internal class Employee
{
private static int idNumber;

public int GetId()
{
return idNumber;
}
public void SetId(int id)
{
idNumber = id;
}
}
/*
D # is 346
D # is 346
*/
13y ago
Thank you for your explanation.
Vulpes13y ago
There is no problem in an instance property accessing a static field which is why there's no error if you make idNumber static.

However, the program no longer makes much sense.

If you create another Employee object and call SetId with a value (say) of 346 and now call GetId on the original object, you'll find that this now returns 346 as well!

This is because there's now only one idNumber field for the entire class, not one per instance as there should be.
Jignesh Trivedi13y ago
hi,
why you expecting error here?
in this code you are calling GetId method which is public and accessable with in module or assambaly level.
if you are accessing private member directly than it gave error....
as per my knowledge, all member of class are initialize when you create object of the class.
hope this will help you.