Static variable is single for class or single for JVM
Hello,
I have doubt, static variable is single for class or single for JVM. as per my knowledge static variable is single for class, but suposse i have an web application (war of an application ) i deployed the application twice with different context, supose yahoo and yahoo1. but the ditrectory structure and classes are same, if i have a statc variable in
a classof an application, if i change the static variable of one class of an application wether it will change the static value of the class of another application.
Example
yahoo -> web-inf -> classes ->MainPackage-> MyStaticClass-> static int i=9;
yahoo1 -> web-inf -> classes ->MainPackage-> MyStaticClass-> static int i=6;
if i change the static value i in yahoo application to i=5;
at the same time if i access the value i in yahoo1 application what i will get (wether 5 or 6).
Thanks.
A static variable is 'single' in its class.
A Class is 'single' in its ClassLoader.
There can be many ClassLoaders per JVM.
There can be many applications per JVM. Each one generally has its own ClassLoader.
Ergo there can be many instances of a Class, and therefore many instances of its static data.
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Hi,
I have a simple class that declares a static variable x...
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I have a simple class that declares a static variable
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System.out.println(DeclareStatic.x);
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static, there is only 1 copy of this static
variable(x), shared amongst all objects. Therefore,
when I attempt to modify this value with a direct
reference (DeclareStatic.x =20;), why isn't the
change refelected in other classes which access the
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Java inherited static operations on static variables
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Rephrasing:
How does one allow a static method defined in a base class, that can already operate (read/modify) on its own static variables, be inheritable in the subclasses, so that they too can use this method to operate on their over-ridden static variables, without the subclasses having to redefine them ?
Partial Problem Definition:
Way before any instances of some of the above-discussed classes are created, the classes should be able to fill in a common static variable with data that is unique to the particular class in question. Especially when these so-called static variables are declared final. Therefore, a superclass (in this case the root) can define this method once, and all subclasses would inherit this class method during their class-object initialization and accordingly fill in their 2 cents worth of value in a given static variable - which in this case will have the same name in all the classes involved. This static variable can represent anything - time-of-class-creation, class-level random number etc.,
An apparently silly example:
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Edited by: Matt0000 on Apr 17, 2008 2:21 PM -
Implement interface with static variable
Hello all
I want to create a class that has a static variable. In this class I also want to create a static function to change this static value. So I donot have to create any object when change the static variable.
My problem is that this class should implement an interface (using facade pattern). As it implements an interface, it cannot have any static function in it.
How I can overcome this problem. please help
Many thanks
shuhuMy problem is that this class should implement an interface (using facade pattern).
As it implements an interface, it cannot have any static function in it.Any class (including one that implements an interface) can have static methods.
Do you mean you want the static method to be part of the interface? In this case you have a problem. Perhaps you should use an abstract class instead of an interface (the class could possibly implement the interface). Or perhaps you should rethink the need to have a static method. -
What is static variable. what is difference between static variable and public variable?
Static variables belong to the Class. Non-static variables belong to Class instances.
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So they are quite different thing. You can have Static variables, Public Static variables, and Private Static variables... -
Global static variable. I just CANNOT get global for everything
Hi,
I copied a connection pool example from oracle web site. It uses static variable. Its not a servlet, its a javabean. I can run a million times in one session and everything is great. If I open up another session, it creates another instance and creates more connections when it should be seeing the previous instance.
My question is how to make a static variable global to the entire application? Do i have to initialize it in the servlet container? All im doing is calling a JSP page which calls this bean. If instance is null, create 5 new connections. Well like i stated above, it works for a single session. It appears that each session gets its own instance. I have been working and debugging this for a long time and I just cannot come up with a solution...
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Thanks as alwaysDeclar it as static within the servlet class.
public class MyServlet extends HttpServlet {
public static ConnectionPool pool;
Then you can access it from any JSP/Servlet using MyServlet.pool but you may have to import the class into the JSP/Servlet.
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Using a static variable declared in an applet in another class
Hi guys,
I created an applet and i want to use one of the static variables declared in teh applet class in another class i have. however i get an error when i try to do that...
in my Return2 class i try to call the variable infoPanel (declared as a static JPanel in myApplet...myApplet is set up like so:
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myApplet.infoPanel.removeAll();
myApplet.infoPanel.add(functionForm2.smgframeold);
myApplet.infoPanel.validate();
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here are some of the errors i get
dummy/Return2.java [211:1] package myApplet does not exist
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myApplet.infoPanel.add(functionForm2.smgframeold);
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myApplet.infoPanel.validate();
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dummy/Return2.java [214:1] package myApplet does not exist
myApplet.infoPanel.repaint();
^
please help! thanks :)I don't declare any packages though....i think it just doesn't recognize myApplet for some reason..
other errors i got compiling are:
dummy/Return2.java [82:1] cannot resolve symbol
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How can I write an instance of a class in a static variable
Hi !
I have an instance of a class
Devisen dev = new Devisen();
In an other class I have a static method and I need there the content of some variables from dev.
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I get the errormessage, that the I cannot use the Not-static variable dev in a static variable.
I understand that I cannot reference to the class Devisen because Devisen is not static I so I had to reference to an instance. But an instance is the same as a class with static methodes. (I think so)
Is there a possibility, if I am in a static method, to call the content of a JTextField of an instance of a class ?
Thank you WolfgangHallo, here is more code for my problem:
class Login {
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HOW TO GET THE CONTENT OF field2 HERE ?
One solution ist to give the instance to the static function, with the keyword "this"
if (!Check.check_field2(this)) return;and get the instance
public static void check_field2(Devisen dev)BUT is that a problem for memory to give every method an instance of the class ? I have 50 fields to control and I dont want do give every check_method an instance of Devisen, if this is a problem for performance.
Or do I only give the place where the existing instance is.
Hmm...?
Thank you Wolfgang
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