Java

[Glenn]

Why can't the following code access class instance variables
public static void main(String[] arg)

this main method is inclosed in my class definition. KI have instance variables
that the class uses to move data between methods, however under the main
function when I try to access an instance variable it gives me an error saying
that static method main() can not access instance variable. My question is
why not?

[Randy Charles Morin]

Any method with the static attribute has this issue. The reason is that
static methods don't have instance data.
--
Randy Charles Morin
Author of Programming Windows Services
http://www.kbcafe.com

Feel free to contact me by private email or messenger
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"Glenn" <gplummer@telusplanet.net> wrote in message
news:3bfd0172$1@147.208.176.211...
>
> Why can't the following code access class instance variables
> public static void main(String[] arg)
>
> this main method is inclosed in my class definition. KI have instance
variables
> that the class uses to move data between methods, however under the main
> function when I try to access an instance variable it gives me an error
saying
> that static method main() can not access instance variable. My question is
> why not?

[Robert]

Glenn,

This is an over-simplified response but, basically, the inability of static
methods to access instance variables has to do with the difference between
a static variable and an instance variable.
Instance variables belong to a single instantiation of the class and do not
exist until that instance is created.
Static variables belong to the class as a whole (thus the term class variables)
and are created as soon as the class is in focus (These variables "belong"
to every instance of the class. Changing its value within one instance affects
the value seen by all instances).
When you call a static method, it has no way of knowing if an instance variable
has been created yet; therefore, it may be attempting to work on something
that doesn't exist.
A simple rule of thumb: static methods can only call static variables.

"Glenn" <gplummer@telusplanet.net> wrote:
>
>Why can't the following code access class instance variables
>public static void main(String[] arg)
>
>this main method is inclosed in my class definition. KI have instance variables
>that the class uses to move data between methods, however under the main
>function when I try to access an instance variable it gives me an error
saying
>that static method main() can not access instance variable. My question
is
>why not?