Static fields storage area

Hi,
local variables are stored on the stack which is private to each thread, all classes instaces are stored on the heap which is shared amongst all threads,
so where are static class variables stored? they're not instances and they are shared amongst all threads....

In older versions of the JVM the memory areas could be divided, Method Area and the heap. In the new implementations however there is no such segregation.vm spec, section 3.5.4 supports exactly what you said:
Although the method area is logically part of the heap, simple implementations may choose not to either garbage collect or compact it.
yet I can't find a clear explanation in there regarding static fields storage....
I guess it doesn't really matter, since the destinction between the method area and the heap is not mandated by the spec...

Similar Messages

Static fields

Can anyone tell me how compiler compiles static or 'final static' fields? Are they holding memory for whole period time of process, or when they're dereferenced, memory will be reclaimed during the process?
Thanks

I am fraid last response misunderstood my question
and comments. Say there are 5000 static integers in
application. It is 5000 bytes. Then there are 5000
static String fields and each has 40 characters (each
one is two bytes). Total static String may have
400000 bytes. Each time the class that contains these
fields is referenced at run time they take up memory.So are you saying that if these fields are not static? It wouldnot take memory? Or are you suggesting that there would always be only one instance of each of these classes so you wouldnot take more space if these fields are not static?
So when application runs forever, it will have a
great chance all these static will be loaded into
memory. So total is 405K bytes that is 'permanently'
stay in memory. You can claim this still a small
amount. But this is just an example and everythingFirst of all its totally insignificant as to how much memory is being taken. The reasons under consideration for declairng a variable static are totally different from what you are assuming but even if you think this way let me tell you this much making them member variables would take more memory since now these variables would be associated with their respective instances and not the class object. And donot tell me that each of these classes is going to have only on instance, so multiply the value with the no. of instances, if you could tell how many instances you would have.
is relative, depending on runtime system. So this is
my original questions: if I want to do something to
save a little bit memory that is permanently occupied
by these static stuffs. But I like to know how
compiler and runtime work: is that true if class is
dereferenced, static field memory will be also
reclaimed? If that is true, I don't need worry (that
means these static fields do not 'permanently' stay
in memory. If not true, I will review these fields toThis question has been answered in my previous post.
see which one could be defined as instance fields or
even defined on stack. The trade off always on
allocate memory on globe heap and keep reference to
it, or create object as needed.
From your comments, seems you think both static and
instance fields can be reclaimed memory if they are
dereferenced (only difference is static is one copy
and instance has multiple - that's obviously and not
question we need discuss)Again you are wrong over here. Read the replies posted again. Secondly I repeat members are not defined static or regular based on the constraints you have in mind and secondly, the way you are thinking that the memory model works is totally wrong. To cut the story short you would not save any memory but making these members regular (non static) On the other hand you might break things by stepping into unknown terrotory since you are not trying to comprehend why were they made static in the first place.

Static fields ARE being serialized

Hi there,
I wrote a small test class that serializes an object, writes the serialized object to file, read the serialized object from the file and then deserialize the object. The object being serialized contains normal fields, a transient field, and a few 4 static fields with varying access modifiers. For some reason the static variables ARE being serialized. From what I've read this should not happen, and for very good reasons.
Here is the object being serialized:
package serialization;
import java.io.Serializable;
import java.util.Formatter;
public class MySerializableObject implements Serializable {
     private static final long serialVersionUID = 1L;
     private int a = 1;
     private int b = 2;
     private transient int c = 3;
     static public int d = 4;
     static protected int e = 5;
     static private int f = 6;
     static int g = 7;
     @Override
     public String toString() {
          Formatter formatter = new Formatter();
          formatter.format("a=%1$s b=%2$s c=%3$s d=%4$s e=%5$s f=%6$s g=%7$s", a,b,c,d,e,f,g);
          return formatter.toString();
     public void setNewD(int newVal) {
          d = newVal;
}And here is the code that does the serialization:
package serialization;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
public class FileContentsObjectSerializer {
     File file;
     public FileContentsObjectSerializer(String name) {
          this.file = new File(name);
          if (this.file.exists()) {
               this.file.delete();
          try {
               this.file.createNewFile();
          } catch (IOException e) {
               e.printStackTrace();
     public void serialize(Object o) throws IOException {
          FileOutputStream fos = new FileOutputStream(this.file);
          ObjectOutputStream oos = new ObjectOutputStream(fos);
          oos.writeObject(o);
          oos.close();
          fos.close();
     public Object deserialize() throws IOException, ClassNotFoundException {
          FileInputStream fis = new FileInputStream(this.file);
          ObjectInputStream ois = new ObjectInputStream(fis);
          Object o = ois.readObject();
          fis.close();
          ois.close();
          return o;
     public static void main(String args[]) {
          MySerializableObject mso = new MySerializableObject();
          mso.setNewD(100);
          System.out.println("Object being serialized:"+mso.toString());
          FileContentsObjectSerializer ofs = new FileContentsObjectSerializer("c:/temptest.txt");
          try {
               ofs.serialize(mso);
               MySerializableObject result = (MySerializableObject) ofs.deserialize();
               System.out.println("Deserialized Object:    "+result.toString());
          } catch (Exception e) {
               e.printStackTrace();
}And here is the results I get:
Object being serialized:a=1 b=2 c=3 d=100 e=5 f=6 g=7
Deserialized Object:    a=1 b=2 c=0 d=100 e=5 f=6 g=7As you can see, both results are exactly the same, even though the setNewD value is not called on the deserialized object.
Any ideas?

You are misinterpreting the result. Try this main instead:
    public static void main(String args[]) {
        MySerializableObject mso = new MySerializableObject();
        mso.setNewD(100);
        System.out.println("Object being serialized:"+mso.toString());
        FileContentsObjectSerializer ofs = new FileContentsObjectSerializer("c:/temptest.txt");
        try {
            ofs.serialize(mso);
            mso.setNewD(-100); //a-oogah!
            MySerializableObject result = (MySerializableObject) ofs.deserialize();
            System.out.println("Deserialized Object:    "+result.toString());
        } catch (Exception e) {
            e.printStackTrace();
    }

How can I share a static field between 2 class loaders?

Hi,
I've been googling for 2 days and it now seems I'm not understanding something because nobody seems to have my problem. Please, somebody tell me if I'm crazy.
The system's architecture:
I've got a web application running in a SunOne server. The app uses Struts for the MVC part and Spring to deal with business services and DAOs.
Beside the web app, beyond the application context, but in the same physical server, there are some processes, kind of batch processes that update tables and that kind of stuff, that run once a day. Theese processes are plain Java classes, with a main method, that are executed from ".sh" scripts with the "java" command.
What do I need to do?
"Simple". I need one of those Java processes to use one of the web app's service. This service has some DAOs injected by Spring. And the service itself is a bean defined in the Spring configuration file.
The solution is made-up of 2 parts:
1. I created a class, in the web app, with a static method that returns any bean defined in the Spring configuration file, or in other words, any bean in the application context. In my case, this method returns the service I need.
public class SpringApplicationContext implements ApplicationContextAware {
     private static ApplicationContext appContext;
     public void setApplicationContext(ApplicationContext context) throws BeansException {
          appContext = context;
     public static Object getBean(String nombreBean) {
          return appContext.getBean(nombreBean);
}The ApplicationContext is injected to the class by Spring through the setApplicationContext method. This is set in the Spring configuration file.
Well, this works fine if I call the getBean method from any class in the web app. But that's not what I need. I need to get a bean from outside the web app. From the "Java batch process".
2. Why doesn't it work from outside the web app? Because when I call getBean from the process outside the web app, a different class loader is executed to load the SpringApplicationContext class. Thus, the static field appContext is null. Am I right?
So, the question I need you to please answer me, the question I didn't find in Google:
How can I share the static field between the 2 class loaders?
If I can't, how can I load the SpringApplicationContext class, from the "Java batch process", with the same class loader my web app was started?
Or, do I need to load the SpringApplicationContext class again? Can't I use, from the process, the class already loaded by my web app?
I' sorry about my so extensive post...
Thank you very much!

zibilico wrote:
But maybe, if the web service stuff gets to complicated or it doesn't fulfill my needs, I'll set up a separate Spring context, that gets loaded everytime I run the "Java batch process". It'll have it's own Spring configuration files (these will be a fragment of the web app's config files), where I'll define only the beans I need to use, say the service and the 2 DAOs, and also the DB connection. Additionally, I'll set the classpath to use the beans classes of the web app. Thus, if the service and DAOs were modified in the app server, the process would load the modified classes in the following execution.You'll almost certainly have to do that even if you do use RMI, Web services etc. to connect.
What I suggest is that you split your web project into two source trees, the stuff that relates strictly to the web front end and the code which will be shared with the batch. The latter can then be treated as a library used by both the batch and web projects. That can include splitting Spring configuration files into common and specific, the common beans file can be retrieved from the classpath with an include. I regularly split web projects this way anyway, it helps impose decoupling between View/Controller and Model layers.
On the other hand, you might consider running these batch processes inside the web server on background threads.

Adobe Reader files missing information in static fields after being emailed?

Hello, I have emailed the same person three seperate times with an attached PDF file that does have some fillable fields and some static fields. One time I email them the file, and the data in the static fields has been changed, but the fillable fields are the same, so I emailed it again and this time all the fields are completely blank, any ideas?

Email transmissions can do all kinds of things, including attachments getting damaged or lost. Far better and safer is to use a file sharing service like Acrobat.com, Dropbox, Google Drive, ..., then send the link by email.

Watching all fields that are in scope using JPDA

Hi,
I'm helping develop a debugger using JDI and have a question about watching certain types of variables that are in scope.
I can watch local variables by getting the current thread's StackFrame and can watch static fields of outer classes by getting their corresponding ReferenceTypes. However, I can't find a good way to watch non-static fields of outer classes that aren't shadowed.
Example. Debugging the following code:
class A {
int x = 5;
class B {
public void foo() {
System.out.println("x = " + x);
public void callFoo() {
B myB = new B();
myB.foo();
The result of calling callFoo on an instance of A is "x = 5" as it should be.
Clearly the method foo() can see what x is. However, it seems to me that to watch the value of x (a non-static field) at any point while I'm debugging, I have to have use the thisObject() method of the appropriate StackFrame and then call getValue() with x. However, if my current thread is suspended within the foo() method, it may not always be possible to retrieve the correct StackFrame (e.g. if foo() is called from some other class such as my debugger event handling thread).
Basically, it'd be nice if you could point out that I'm just not seeing some nice call like getValue(Field f) that will get the value of an instance field that is anywhere in scope, especially those in outer classes. Or if you see anything I'm missing or another way to watch instance fields in outer classes, your help would be greatly appreciated!
James

I'm helping develop a debugger using JDI and have a
question about watching certain types of variables
that are in scope.You would do this by creating a com.sun.jdi.request.WatchpointRequest
and restricting the scope of the request to the object specified. This
is done by adding filter(s) to the request before it is enabled. For
more information, take a look at:
http://java.sun.com/j2se/1.4.1/docs/guide/jpda/jdi/com/sun/jdi/request/WatchpointRequest.html#addInstanceFilter(com.sun.jdi.ObjectReference)

The static field should be accessed in a static way

Hello,
I am developing a java app in eclipse and I am getting the error message:
The static field Calendar.DAY_OF_WEEK should be accessed in a static way
I am trying to get the first day of the first week in the current month, here is my code:
GregorianCalendar firstDayOfThisMonthCalendar = new GregorianCalendar(Calendar.YEAR, Calendar.MONTH, 1);
int firstDayOfThisMonth = firstDayOfThisMonthCalendar.DAY_OF_WEEK;I though the problem was that I'm supposed to write the code like this:
firstDayOfThisMonthCalendar.get(Calendar.DAY_OF_WEEK); but then I get the wrong value back

That's what I critice about u people, always ready to
complain, It's not complaining. It's pointing out problems with your code. You should thank him.
but do u put the code in here the way that
someone could read it ? Easy to say 'use
simpleDateFormat. Oh, careful, January returns 0, not
1'.Using SimpleDateFormat is an easier and more correct way to do it. Trying to use the numerical value of the month constants is incorrect coding. You should thank him for educating you.
Why can't u write the code in here so there's no
chance that somebody will ask again.Such code is not possible. No matter what code you write, somebody can misunderstand it.
If you write the code correctly--using SimpleDateFormat--then the code will be correct (which is the most important criteria) and clear (which is important, but not as important as correctness).
But if you prefer to think that your way is always perfect and are afraid to admit your mistakes and learn from them, that's your prerogative.

Using Objects to Initialize Static Fields: Good or Bad

I have a Command interface and a bunch of Commands that implement it (i.e. CmdJoin,CmdQuit). These Commands' settings change at runtime (i.e. required access levels, String identifiers). I don't want to have to store an instance of each Command in a database to save their settings , so instead I'm using the obvious solution: making static fields in these commands for these settings. This way, I can use a Simple Factory to return a Command, change its settings, execute it, and forget it, and still have the settings for that Command apply to all Commands. Yet I want to be able to modify and access fields of different Commands polymorphically. How can I have these commands' settings-related fields be static while modifying and accessing these fields polymorphically?
Here's what I have though of. First of all, interfaces can't have static methods. Secondly, neither can abstract classes. I also can't extend a base class which implements these settings-related fields and their interface, because then the fields would belong to all child classes of this base class, whereas I just want it to belong to a certain child class of the base class (i.e. all instances of CmdJoin or CmdQuit).
I've thought of two solutions.
The first is implementing a concrete interface in an abstract base class (getting rid of the Command interface) and overriding it in child classes, so that I can use the interface of the base class and the fields of the child classes.
The second is having no base class, and just a bunch of Commands implementing the interface with their own static fields. I would initialize these fields by passing arguments to their constructors.
These solutions seem very sloppy though! Are there any better ways?

To clarify, I want all objects of type A to be able to respond to a static method declared in type A yet still remember their implementation of this static method. I provided two solutions that I have thought of, and I find them sloppy, so I'm asking if there's a better way.

Generics in static fields

Hi, I am trying to make a class which has some generic fields. I understand that it would not work just like that as the compiler has no way what the generic fields should actually be in a static context.
I want to use the generic class as an abstract class which would be extended, so that way the generics should be resolvable. Is there any way to make this work this way or should I not use generics and go type unsafe?
This is what I want to do in code:
abstract class ClassToBeExtended<A>
     static A a;
class UsingTheOther extends ClassToBeExtended<String> {}

It is supposed to be a class that adds relations between other classes:
// Simplified
class RelationBetweenAandB extends TheClass<A, B> {}
class SomeOtherClass
void foo()
    A a = new A();
    B b1 = new B();
    B b2 = new B();
    RelationBetweenAandB.add(a, b1);
    RelationBetweenAandB.add(a, b2);
    new YetAnotherClass().listRelationsOf(a);
class YetAnotherClass
public void listRelationsOf(A a)
      for (B b : RelationBetweenAandB.allRhs(a))
      ; // Iterate through b1 and b2
}Having static fields will make the relation useful from anywhere in the application, if it is not static then all the objects that are going to be used in a relation have to instantiate the class which wlll probably introduce a lot of overhead.
abstract class SomeClass<A extends OtherClass>
static OtherClass a;
} Would require me to have Object in stead of OtherClass because I want all types of object to be in a relation, which is what I meant by going type unsafe :)
Message was edited by:
SavageNLD
Added some more reasoning about why I want static fields

WM - Storage type 001 is not suitable as an interim storage area -

Hi,
When i'm doing Migo, the blw error has came, pls advise , how solve it..
seems, some where i made wrong config.. These process i was trying in our ides server..
Storage type 001 is not suitable as an interim storage area
Message no. L9022
Diagnosis
You have attempted to execute a posting to a dynamic coordinate in a storage type for which a putaway strategy is defined. Dynamic coordinates, however, are provided only for storage types without a putaway strategy.

thanks Raman
pls tell me now , where i have to check the config.. and where i may did the mistake.
for ur info, ref to sdn A08- conf guide as per blw , i made the conf..
3.1 Full WM Basic Settings
3.1.1 Defining Control Parameters for Warehouse Number
3.1.2 MM-IM Storage Location <-> Warehouse Number     J01
3.1.3 Defining Storage Type                                              001- high rack system
3.1.4 Defining Storage Section                                            001- Fastmoving
3.1.5 Defining Storage Bin Types                                   P1-BIN HEGIHT 1 MTR
3.1.6 Defining Blocking Reasons                                           1
3.1.7 Defining Storage Bin Structures
3.1.8 Defining Storage Type Indicators                                1
3.1.9 Defining Storage Unit Types                                    E1
3.1.10 Defining Storage Section Indicator                        001- Fastmoving
3.1.11 Defining Bulk Storage Indicator                                      B1
3.2 Strategies
3.2.1 Activating Storage Type Search
3.2.2 Activating Storage Section Search
3.2.3 Activating Storage Bin Type Search
3.2.4 Defining Sort Sequence for Putaways (Cross-line Stock Putaway) Definition of Sort Field in Storage Bin
3.2.5 Defining Strategy for Pallets
3.2.6 Defining Putaway Strategy for Bulk Storage
3.2.7 Defining Strategy for Stringent FIFO
3.2.8 Defining Strategy for Large/Small Quantities Determining Search Sequence
3.3 Activities
3.3.1 Defining Requirement Categories
3.3.2 Defining Shipment Types
3.3.3 Defining Movement Types
3.3.4 Defining Stock Transfer and Replenishment Control Defining Replenishment Control for Storage Type
3.3.5 Setting up 2-Step Picking
3.3.6 Defining Confirmation
3.3.7 Print Control
3.3.8 Defining Default Values
3.3.9 Defining Types for Storage Type
3.3.10 Defining Difference and Document Limit
3.3.11 Clearing Difference (Interface with IM) MM-IM Movement Types for Clearing Inventory
3.3.12 Clearing Difference (Interface with IM)  Do Not Allow Clearing in Storage Types
3.4 Interfaces
3.4.1 Allowed Negative Stocks in Interim Storage Types Allowing Negative Stock for Each Storage Type
3.4.2 Shipping Shipping Control per Warehouse Number
3.4.3 Shipping  Requirement Types of Delivery Documents
3.4.4 2-Step Picking
3.4.5 Creating Automatic Transfer Order
3.5 Manual Activities
3.5.1 Maintaining Number Range and Assignment
3.5.2 Maintaining Number Range for Physical Inventory
3.5.3 Creating Storage Bins
3.5.4 Generating Interim Storage Bin
Edited by: UJ on Mar 4, 2009 7:16 AM

Interim storage area

dock doros and staging areas are they linked to interim storage area? for example while doing a receipt for a PO based on delivery which has dock door and staging area assigned then what happens to interim storage area '902'?
Please clarify.

so it means i need to specify the interim storage type to the 311 in destination field
and i have aslo done exactly like that but now the problem coming is system is not able to pick the goods from sloc 00 & storage type high rack(from here i want to tranfer the goods to the sloc 01 storage type shelf )
syetm is showing error 'storage bin z1 not found '
and z1 is the name of my warehouse
in z1 i have high rack ,shelf, interim for stock transfer storage type ........................so what i am understanding is interim storage type has to be mentioned in dest. for movement type 311
and i have already maintaineed the stock palcement indicator ,stock removal indicaotr , storage section in material master and search tabls for storage type high rack (for stock removal as well as for sotck put way and ).....storage bin is already created
i if u can give ur mail id i can send u screen shots then u can understand my problem much better(if possible for you) ......................actually i am trying to learn warehouse for past 5 days but i am stcuk in 311 movement type

StreamTokenizer static fields

Maybe this is a stupid question but why does this compile without problems:
Reader r = new BufferedReader(new InputStreamReader(System.in));
StreamTokenizer tok = new StreamTokenizer(r);
          // StreamTokenizer tok = new StreamTokenizer(System.in);
          try{
               while (tok.nextToken() != StreamTokenizer.TT_EOF){
                    switch (tok.ttype) {        // ttype is token type
                         case StreamTokenizer.TT_NUMBER:
                              System.out.println("number " + tok.nval);
                              break;
     ....But this:
Reader r = new BufferedReader(new InputStreamReader(System.in));
StreamTokenizer tok = new StreamTokenizer(r);
          // StreamTokenizer tok = new StreamTokenizer(System.in);
          try{
               while (tok.nextToken() != StreamTokenizer.TT_EOF){
                    switch (tok.ttype) {
                         case tok.TT_NUMBER: // nval is numeric value
                              System.out.println("number " + tok.nval);
                              break;
     ....                    gives the following compiling error:
constant expression required
    case tok.TT_NUMBER: value
           ^
1 errorI thought static fields can be access both through the name of the class and objects of it.
The version that doesn't compile comes from a book which makes it slightly more confusing.

excuse my wording. I have been using >= mostly, though
I do know that > exists. If I replace the >
with >= and compile there are no errors. But I also
get the following errors with the >
# javac TestLight.java
TestLight.java:13: ')' expected
if (a.KWH_PRICE > 0)
^
TestLight.java:13: not a statement
if (a.KWH_PRICE > 0)
^
TestLight.java:13: ';' expected
if (a.KWH_PRICE > 0)
^
TestLight.java:13: cannot resolve symbol
symbol : variable gt
location: class TestLight
if (a.KWH_PRICE > 0)
^
4 errorsYou really get errors then ?
Very strange, I don't get any.....

Avoid assigning to servlet static fields without using a shared lock??

Hi
i received the following warning on my code, does anyone give me a help on this? Thanks
"Avoid assigning to servlet static fields from javax.servlet.Service.service () without using a shared lock."
And my code are as follow:
public class MyDataSource {
    private static DataSource ds = null;
    public static DataSource getDataSource() throws NamingException, Exception
        if (ds==null){
               InitialContext ctx = new InitialContext();
            try{
                synchronized(getDataSource()){
                if(ds==null){
                    ds = (DataSource) ctx.lookup(SysProperties.ds);
            } catch (Exception ex) {
                throw new Exception("DBConnection Exception: " +ex.toString());
            }finally{
                    if(ctx !=null){
                        ctx.close();
        return ds;
}

The service method of a servlet is multi-threaded to handle multiple requests. Hence,any static or public fields accessed by the service method should be restricted to a single thread access (for example using synchronized keyword) to make it thread-safe. That is why you are getting the warning message.

Static fields on different machines

Hi:
Let us say I have a class
public class Client(){private int static someField;
I know if you are running Client.java on a single machine, obviously you will only get ONE incarnation of someField because it is static.
Now, let us say I run the Client.java on different machines, then there will be one someField genearted per each JVM , is that right??
can someone confirm??
I did a serach on Static field on the Forum, but nobody really touched on running it on different machines, so I thought I ask...

Yes, that's right.

How to schedule multiple reports with different local to change static field language ?

Hi all,
we have requirement that we will place multiple schedule request on same server ,This schedule request will be different local setting with parameter value like: en-GB,en-US,Chinese...etc .We used translation Manager for this and it takes this parameter and change report language for static fields.
problem is that ,on server it is not working properly,we tested for one report .if we pass prompt value to change local setting in report the we need to log off and login again in CMC to reflect new local or on BI Launchpad we need to refresh page then it shows new language.
How we can do this with multiple scheduled report which will have different local value like en-GB,en-US,Chinese,German....?These schedule request are getting placed in server by one user .
Please help us with sample code.
Thanks
Madan

Hi,
The only approach I can think of is to create a template report which uses variables
For each column you would need to variable
v_columnAName and v_columnAValue
v_columnAName would have a if statement in it
=if([client]="clientA" or [client]="clientC";NameOf([firstName]);if([client]="clientB";NameOf([SSN]);NameOf([lastName]));
v_columnA would have a if statement in it
=if([client]="clientA" or [client]="clientC";[firstName];if([client]="clientB";[SSN],[lastName]));
This would only work when you had a small set of clients.
This might be more managable if it was done in the universe
Regards
Alan

Static fields storage area

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