Re: Static vs Instance Method Question

[Jon Skeet [C# MVP]]

On Aug 11, 5:11*am, "Peter Duniho" <[e-mail]>
wrote:

As Arne says, it's mainly a matter of an arbitrary choice in the language*
to help make sure it's obvious what type of method is being called. *Not *
that IMHO it's so important that one knows a method is static vs instance, *
but rather than one may expect different behaviors (especially with *
respect to polymorphism) when calling a method via an instance rather than *
via a type name.

By requiring the static calls to be made using the type name instead of an *
instance, it's a lot more clear in code what's going on.

Exactly. My favourite example is Thread.Sleep. Suppose this code were
valid (its equivalent in Java is, for example):

ThreadStart ts = SomeMethodToRun;
Thread thread = new Thread(ts);
thread.Start();
thread.Sleep(500);

What does it *look* like that call to Sleep is doing? To me, it looks
like it's acting on the newly created thread. By forcing you to write
Thread.Sleep, C# makes it obvious that you can't call Sleep on an
arbitrary thread - the operation only makes sense for the current
thread, which can be determined statically.

Jon

[Peter Duniho]

On Mon, 11 Aug 2008 23:20:17 -0700, Arcticool <ar*******@hotmail.com>
wrote:

[...]
public class Tester
{
int i = 32; //compile error, must be static, makes sense...
static void Main()
{
static int j = 40; //for some reason throws compile error.
Console.WriteLine(i);
Console.WriteLine(j);
}
}

Is 'j' implicitly static by virtue of being inside a static method? Or
is static just not valid inside a method?

The latter. C# just doesn't have static locals (and the variable "j" is
definitely not implicitly static, at least not in the sense that a static
local would be in C++).

I'm confused by your comment about the compile error for the instance
member field "i" though. You would get an error about the field needing
to be static if the class itself was static, but given the code you
posted, I think that line should compile fine. What error are you getting
there, exactly? Do you get it with exactly the code you posted?

Pete

[Arcticool]

Peter Duniho wrote:

On Mon, 11 Aug 2008 23:20:17 -0700, Arcticool <ar*******@hotmail.com>
wrote:

>[...]
public class Tester
{
int i = 32; //compile error, must be static, makes sense...
static void Main()
{
static int j = 40; //for some reason throws compile error.
Console.WriteLine(i);
Console.WriteLine(j);
}
}

Is 'j' implicitly static by virtue of being inside a static method? Or
is static just not valid inside a method?

The latter. C# just doesn't have static locals (and the variable "j" is
definitely not implicitly static, at least not in the sense that a
static local would be in C++).

I'm confused by your comment about the compile error for the instance
member field "i" though. You would get an error about the field needing
to be static if the class itself was static, but given the code you
posted, I think that line should compile fine. What error are you
getting there, exactly? Do you get it with exactly the code you posted?

Pete

Oh that's probably my bad I was playing with some constructor stuff and
tried to simplify the code for the post here. Anyway here is the
original code:

public class Tester
{
int j = 32;
static void Main()
{
Console.WriteLine(j); //j here is underlined in blue.

System.DateTime currentTime = System.DateTime.Now;
Time t = new Time( currentTime );
t.DisplayCurrentTime();

Time t2 = new Time( 2007, 9, 18, 11, 45 );
t2.DisplayCurrentTime();

Time t3 = new Time();
t3.DisplayCurrentTime();
}
}

//An object reference is required for the non-static field, method, or
property 'Initializer.Tester.j'
BTW, I'm using Visual C# Express edition.

Jack

[Peter Duniho]

On Mon, 11 Aug 2008 23:54:33 -0700, Arcticool <ar*******@hotmail.com>
wrote:

[...]
//An object reference is required for the non-static field, method, or
property 'Initializer.Tester.j'

Okay, well that's a completely different line of code and a different
error. It's not complaining that "j" has to be static per se, though
that's certainly one way to fix it. It's just pointing out to you that to
refer to an instance member, you need to have an instance, which in a
static method you don't.

Pete

[Arcticool]

Peter Duniho wrote:

On Mon, 11 Aug 2008 23:54:33 -0700, Arcticool <ar*******@hotmail.com>
wrote:

>[...]
//An object reference is required for the non-static field, method, or
property 'Initializer.Tester.j'

Okay, well that's a completely different line of code and a different
error. It's not complaining that "j" has to be static per se, though
that's certainly one way to fix it. It's just pointing out to you that
to refer to an instance member, you need to have an instance, which in a
static method you don't.

Pete

Hmm, for some reason my last response didn't post. Anyway, I see what
you're saying. I can make j static or I can create an instance of Tester
and then call Tester.j.

Thanks to everyone for the replies,

Jack