Static variable reference.

I have written a small synchronized code
class Foo implements Runnable {
private byte[] myLock = new byte[0];
public static void display(Foo f){
synchronized(f.myLock){
//Code to lock.
}My question is:
If I use synchronized(f.myLock),how can 'f' refer to a non-static variable
myLock?
Shouldnt static methods refer only to static variables?
Am I missing a point?

f is an instance of Foo, and f.myLock refers to the lock object of that very instance.
If you just write myLock without specifying the object, it refers to the instance against which the current method is executing. But such an instance does not exist for a static method, so you can not use that "unadorned" myLock in a static method.

Similar Messages

Static Variable References

Hello,
I want to create a variable in one class and have other classes alble to share and manipulate this variable without using subclassing. I think that I may be able to do it by declaring a variable static. Will this work, if not how can I accomplish this?
Thanks in advance for your help!!

Yes I'm only sychronizing on this variable, each of
the classes will modify the boolean variable to
indicate if they are about to execute a critical
section of code.You are reinventing the wheel. Synchrionization is built into Java. All you have to do it lock on an Object.
public void example()
   synchronized(this)
      // critical section
      // only one thread can execute this code at a time
}Using a boolean won't work anyway. If two threads read from this varaible at approximately the same time, they may both think they can enter the critical section. In addition, the threading memory model allows that variable to have multiple copies, one for each thread. There is no guarantee when the copies will be refreshed, if ever.

How to reference a static variable before the static initializer runs

I'm anything but new to Java. Nevertheless, one discovers something new ever' once n a while. (At least I think so; correct me if I'm wrong in this.)
I've long thought it impossible to reference a static variable on a class without the class' static initializer running first. But I seem to have discovered a way:
public class Foo {
public static final SumClass fooVar; // by default initialized to null
static {
fooVar = new SumClass();
public class Bar {
public static final SumClass barVar;
static {
barVar = Foo.fooVar; // <<<--- set to null !
}Warning: Speculation ahead.
Normally the initial reference to Foo would cause Foo's class object to instantiate, initializing Foo's static variables, then running static{}. But apparently a static initializer cannot be triggered from within another static initializer. Can anyone confirm?
How to fix/avoid: Obviously, one could avoid use of the static initializer. The illustration doesn't call for it.
public class Foo {
public static final SumClass fooVar = new SumClass(); // either this ..
public class Bar {
public static final SumClass barVar = Foo.fooVar; // .. or this would prevent the problem
}But there are times when you need to use it.
So what's an elegant way to avoid the problem?

DMF. wrote:
jschell wrote:
But there are times when you need to use it. I seriously doubt that.
I would suppose that if one did "need" to use it it would only be once in ones entire professional career.Try an initializer that requires several statements. Josh Bloch illustrates one in an early chapter of Effective Java, IIRC.
Another classic usage is for Singletons. You can make one look like a Monostate and avoid the annoying instance() invocation. Sure, it's not the only way, but it's a good one.
What? You only encounter those once in a career? We must have very different careers. ;)
So what's an elegant way to avoid the problem? Redesign. Not because it is elegant but rather to correct the error in the design.<pff> You have no idea what my design looks like; I just drew you a couple of stick figures.If it's dependent on such things as when a static initializer runs, it's poor. That's avoidable. Mentioning a case where such a dependency is used, that's irrelevant. It can be avoided. I know this is the point where you come up with a series of unfortunate coincidences that somehow dictate that you must use such a thing, but the very fact that you're pondering the problem with the design is a design problem. By definition.
Besides, since what I was supposing to be a problem wasn't a problem, your "solution" isn't a solution. Is it?Well, you did ask the exact question "So what's an elegant way to avoid the problem?". If you didn't want it answered, you should have said so. I'm wondering if there could be any answer to that question that wouldn't cause you to respond in such a snippy manner. Your design is supposedly problematic, as evidenced by your question. I fail to see why the answer "re-design" is unacceptable. Maybe "change the way the Java runtime initializes classes" would have been better?
This thread is bizarre. Why ask a question to which the only sane answer, you have already ruled out?

Error on compile - non-static variable can not be referencedfrom static con

Error on compile happening with addButton?
Thanks
import java.awt.*;
import java.awt.event.*;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JFrame;
public class Log implements ActionListener {
JButton addButton;
public static void addComponentsToPane(Container pane) {
pane.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();
     c.gridy = 3;
c.gridx = 0;
     JLabel callsignLabel= new JLabel("Callsign");
pane.add(callsignLabel, c);
     c.gridy = 3;
c.gridx = 1;
     JLabel nameLabel= new JLabel("Name");
pane.add(nameLabel, c);
     c.gridy = 3;
c.gridx = 2;
     JLabel timeLabel= new JLabel("Time");
pane.add(timeLabel, c);
     c.gridy = 3;
c.gridx = 3;
     JLabel dateLabel= new JLabel("Date");
pane.add(dateLabel, c);
     c.gridy = 3;
c.gridx = 4;
     JLabel frequencyLabel= new JLabel("Freq ");
pane.add(frequencyLabel, c);
     c.gridy = 3;
c.gridx = 5;
     JLabel locationLabel = new JLabel("Country/State");
pane.add(locationLabel, c);
c.gridy = 5;
c.gridx = 0;
     addButton = new JButton("Add");
pane.add(addButton, c);
     addButton.addActionListener(this);

Thank you for the reply
I am new to Java
What is wrong with the way it is coded?The error message tells you what's wrong: You're trying to reference a non-static variable from a static context.
If you don't know what that means, then click the link I provided and look at the results from that google search. You might have to go through a few before you find a satisfactory explanation. And after you've done that, if you have specific questions about things you didn't understand there, please post again.

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.
public static void abc()
{ String text=dev.textfield.getText()
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 Wolfgang

Hallo, here is more code for my problem:
class Login {
   Devisen dev=new Devisen();
class Devisen {
   JTextField field2;
   if (!Check.check_field2()) return; // if value not okay than return
class Check {
   public static void check_field2()
     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

Non-static variable Help needed

Hi, I am creating a multi threaded web server but get the following error
non-static variable this cannot be referenced from a static context
HttpRequest request = new HttpRequest(connectionSocket);
Please could someone help.
Many Thanks
import java.io.* ;
import java.net.* ;
import java.util.* ;
public final class MultiWebServer
public static void main(String argv[]) throws Exception
     // Set the port number.
     int port = 6789;
// Establish the listen socket.
               String fileName;
               ServerSocket listenSocket = new ServerSocket(port);
// Process HTTP service requests in an infinite loop.
while (true) {
     // Listen for a TCP connection request.
     Socket connectionSocket = listenSocket.accept();
// Construct an object to process the HTTP request message.
HttpRequest request = new HttpRequest(connectionSocket);
// Create a new thread to process the request.
Thread thread = new Thread(request);
// Start the thread.
thread.start();
final class HttpRequest implements Runnable
     final static String CRLF = "\r\n";
     Socket socket;
String requestMessageLine;
String fileName;
Date todaysDate;
     // Constructor
     public HttpRequest(Socket socket) throws Exception
          this.socket = socket;
          socket = null;
// Implement the run() method of the Runnable interface.
public void run()
     try {
          processRequest();
     } catch (Exception e) {
          System.out.println(e);
private void processRequest() throws Exception
     // Get a reference to the socket's input and output streams.
     //InputStream is = new InputStream(socket.getInputStream());
     //DataOutputStream os = new DataOutputStream(socket.getOutputStream());
BufferedReader inFromClient =
                    new BufferedReader(new InputStreamReader(
                         socket.getInputStream()));
               DataOutputStream outToClient =
                    new DataOutputStream(
                         socket.getOutputStream());
     // Set up input stream filters.
     requestMessageLine = inFromClient.readLine();
     //BufferedReader br = null;
     // Get the request line of the HTTP request message.
String requestLine = null;
// Display the request line.
System.out.println();
System.out.println(requestLine);
StringTokenizer tokenizedLine =
                         new StringTokenizer(requestMessageLine);
               if (tokenizedLine.nextToken().equals("GET"))
                    fileName = tokenizedLine.nextToken();
                    if ( fileName.startsWith("/")==true )
                         fileName = fileName.substring(1);
File file = new File(fileName);
                    int numOfBytes = (int)file.length();
                    FileInputStream inFile = new FileInputStream(fileName);
                    byte[] fileInBytes = new byte[numOfBytes];
                    inFile.read(fileInBytes);
                    /* Send the HTTP header */
                    outToClient.writeBytes("HTTP/1.1 200 Document Follows\r\n");
                    if (fileName.endsWith(".jpg"))
                         outToClient.writeBytes("Content-Type: image/jpeg\r\n");
                    if (fileName.endsWith(".jpeg"))
                         outToClient.writeBytes("Content-Type: image/jpeg\r\n");
                    if (fileName.endsWith(".gif"))
                         outToClient.writeBytes("Content-Type: image/gif\r\n");
                    if (fileName.endsWith(".html"))
                         outToClient.writeBytes("Content-Type: text/html\r\n");
                    if (fileName.endsWith(".htm"))
                         outToClient.writeBytes("Content-Type: text/html\r\n");
                    outToClient.writeBytes("Content-Length: " + numOfBytes + "\r\n");
                    outToClient.writeBytes("\r\n");
                    /* Now send the actual data */
                    outToClient.write(fileInBytes, 0, numOfBytes);
                    socket.close();
               else
               System.out.println("Bad Request Message");
               todaysDate = new Date();
               try {
                    FileInputStream inlog = new FileInputStream("log.txt");
                    System.out.println(requestMessageLine + " " + todaysDate );
                    FileOutputStream log = new FileOutputStream("log.txt", true);
                    PrintStream myOutput = new PrintStream(log);
                    myOutput.println("FILE -> " + requestMessageLine + " DATE/TIME -> " + todaysDate);
               catch (IOException e) {
               System.out.println("Error -> " + e);
               System.exit(1);
socket.close();

import java.io.* ;
import java.net.* ;
import java.util.* ;
public final class MultiWebServer
public MultiWebServer(){
try{
// Set the port number.
int port=6789;
// Establish the listen socket.
String fileName;
ServerSocket listenSocket=new ServerSocket(port);
// Process HTTP service requests in an infinite loop.
while(true){
// Listen for a TCP connection request.
Socket connectionSocket=listenSocket.accept();
// Construct an object to process the HTTP request message.
HttpRequest request=new HttpRequest(connectionSocket);
// Create a new thread to process the request.
Thread thread=new Thread(request);
// Start the thread.
thread.start();
}catch(IOException ioe){
}catch(Exception e){
public static void main(String argv[]) throws Exception
new MultiWebServer();
final class HttpRequest implements Runnable
final static String CRLF = "\r\n";
Socket socket;
String requestMessageLine;
String fileName;
Date todaysDate;
// Constructor
public HttpRequest(Socket socket) throws Exception
this.socket = socket;
socket = null;
// Implement the run() method of the Runnable interface.
public void run()
try {
processRequest();
} catch (Exception e) {
System.out.println(e);
private void processRequest() throws Exception
// Get a reference to the socket's input and output streams.
//InputStream is = new InputStream(socket.getInputStream());
//DataOutputStream os = new DataOutputStream(socket.getOutputStream());
BufferedReader inFromClient =
new BufferedReader(new InputStreamReader(
socket.getInputStream()));
DataOutputStream outToClient =
new DataOutputStream(
socket.getOutputStream());
// Set up input stream filters.
requestMessageLine = inFromClient.readLine();
//BufferedReader br = null;
// Get the request line of the HTTP request message.
String requestLine = null;
// Display the request line.
System.out.println();
System.out.println(requestLine);
StringTokenizer tokenizedLine =
new StringTokenizer(requestMessageLine);
if (tokenizedLine.nextToken().equals("GET"))
fileName = tokenizedLine.nextToken();
if ( fileName.startsWith("/")==true )
fileName = fileName.substring(1);
File file = new File(fileName);
int numOfBytes = (int)file.length();
FileInputStream inFile = new FileInputStream(fileName);
byte[] fileInBytes = new byte[numOfBytes];
inFile.read(fileInBytes);
/* Send the HTTP header */
outToClient.writeBytes("HTTP/1.1 200 Document Follows\r\n");
if (fileName.endsWith(".jpg"))
outToClient.writeBytes("Content-Type: image/jpeg\r\n");
if (fileName.endsWith(".jpeg"))
outToClient.writeBytes("Content-Type: image/jpeg\r\n");
if (fileName.endsWith(".gif"))
outToClient.writeBytes("Content-Type: image/gif\r\n");
if (fileName.endsWith(".html"))
outToClient.writeBytes("Content-Type: text/html\r\n");
if (fileName.endsWith(".htm"))
outToClient.writeBytes("Content-Type: text/html\r\n");
outToClient.writeBytes("Content-Length: " + numOfBytes + "\r\n");
outToClient.writeBytes("\r\n");
/* Now send the actual data */
outToClient.write(fileInBytes, 0, numOfBytes);
socket.close();
else
System.out.println("Bad Request Message");
todaysDate = new Date();
try {
FileInputStream inlog = new FileInputStream("log.txt");
System.out.println(requestMessageLine + " " + todaysDate );
FileOutputStream log = new FileOutputStream("log.txt", true);
PrintStream myOutput = new PrintStream(log);
myOutput.println("FILE -> " + requestMessageLine + " DATE/TIME -> " + todaysDate);
catch (IOException e) {
System.out.println("Error -> " + e);
System.exit(1);
socket.close();

Static variable declaration in JavaFX

Hello, I'd like to ask how to substitute static key word to declare a variable, that is visible within the current package and accessible without creating an instance of a class, that contains this variable. Because my NetBeans insists that static variable is depricated.
Thank you.

In Foo.fx...
class Foo {
// bar is an instance variable that has public access
public def bar = "bar";
// baz is a "static" variable that has public access
public def baz = "baz";
// someFun is a "static" function
public function someFun() : Void {
}In Main.fx...
println("{Foo.bar}"); // compile error - cannot reference bar from static context
println("{Foo.baz}"); // This is ok - Foo.baz is static
var foo = Foo{}
println("{foo.bar}"); // This is ok. bar referenced from Foo instance

Modifying static variable in 1object dosent effect value in another object

Hi,
I have a simple class that declares a static variable x...
class DeclareStatic
     static int x = 10;
}I have another class that modifies this static variable (x)...
class ModifyStatic
     public static void main(String[] Args)
          DeclareStatic.x = 20;
}The problem I have is when I run the next class to simply print out the static variable x, I get 10 (the originally assigned value), not 20 (the modified value)...
class StaticTest
     public static void main(String[] Args)
          System.out.println(DeclareStatic.x);
}It is my understanding that by definition of being 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 variable?
This also leads to the question how DO I modify a (non final) static variable from an object and have the change reflected in all other objects?
I have spent some time researching this on-line and in my java books to no avail, any help is greatly appreciated as I am studying to sit the SCJP and attention to detail is everything!
Thanks,
Alan Kilbride ;o)

Hi,
I have a simple class that declares a static variable
x...
class DeclareStatic
     static int x = 10;
}I have another class that modifies this static
variable (x)...
class ModifyStatic
     public static void main(String[] Args)
          DeclareStatic.x = 20;
}The problem I have is when I run the next class to
simply print out the static variable x, I get 10 (the
originally assigned value), not 20 (the modified
value)...
class StaticTest
     public static void main(String[] Args)
          System.out.println(DeclareStatic.x);
}It is my understanding that by definition of being
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
variable?Because your test code never makes a reference to the ModifyStatic class. You could delete ModifyStatic from your system and the code would run exactly the same.
Jim S.

Static variable behaviour in memory

Hi,
My question is :
When you compile a java code, does the static variable gets the memory allocated while creating the byte code or is it on run time that a static variable gets the memory allocation and then it is shared for all instances.
Thanks
Melvyn.

Good !!! I expected this question from you.
Instantiation and Initialization are different.
A class or interface type T will be initialized immediately before the first occurrence of any one of the following:
1) T is a class and an instance of T is created.
2) T is a class and a static method declared by T is invoked.
3) A static field declared by T is assigned.
4) A static field declared by T is used and the reference to the
field is not a compile-time constant. References to
compile-time constants must be resolved at compile time to
a copy of the compile-time constant value, so uses of such a
field never cause initialization.
Regards
Raghu

Re: static variables in beans

That's GoF. Again I was responding to the question posted earlier and could not
see it near by and not commenting on yours. I was questioning the original design
of having to keep singletons as static fields in SLSBs.
S
"Cameron Purdy" <[email protected]> wrote:
Is there a problem if you get the singleton (through a static methodas
in GoF) objects in the methods as required and not store it as static
variables in the SLSB?I am acronymically challened ("AC"). What is GoF? I know I've seen it
before, but I can't remember what it means.
Singletons should store their own reference. You should probably have
a
private constructor and a static "instance" accessor.
Peace,
Cameron Purdy
Tangosol, Inc.
http://www.tangosol.com/coherence.jsp
Tangosol Coherence: Clustered Replicated Cache for Weblogic
"sri" <[email protected]> wrote in message news:[email protected]..
>

You are right. An EJB (all kinds) is restricted from using writtable static fields.
Read only fields are allowed but recommended to use 'final' to denote so.
S
"Cameron Purdy" <[email protected]> wrote:
That's GoF. Again I was responding to the question posted earlier and
could not see it near by and not commenting on yours. I was questioning
the original design of having to keep singletons as static fields inSLSBs.
It gets difficult to follow these threads. I use Outlook Express (motto:
"There's no message out there that we can't add a top-post to!") which
isn't
the world's best newsreader.
Regarding static fields in SLSBs, you are right that it is certainly
something to avoid. I believe that some containers even refuse to deploy
EJBs that have static fields like that. (I believe it's a purposed
limitation in the spec.)
Peace,
Cameron Purdy
Tangosol, Inc.
http://www.tangosol.com/coherence.jsp
Tangosol Coherence: Clustered Replicated Cache for Weblogic
"Sri" <[email protected]> wrote in message news:3ea5b88e$[email protected]..
>

Is is better to use static variables?

Hi,
Does anyone know if it's better to use static variables or to use normal variables?
Concerning the size of the code, it seems that declaring a variable as static is more consuming (for example plus 6 bytes for an object reference).
So this could mean that declaring variables as static should be avoided, but what about the execution time?
Some years ago, some javacard gurus were claiming that it's was better to use static variables (less processing required by the JVM to resolve adresses of static variables), but is it still the case?

Hi Lexdabear,
Thanks for the answer.
I did the test (I converted my all code to use static variables and methods as much as possible), and did a bench before and after, on a JCOP31 card.
The conclusion is that today JVMs and processors are much powerful than 5 years ago, and that the difference is really difficult to measure, which anyway is a good thing for us ;-)

Static variables at runtime

dear friends
how to delete the static variables and objects after using them ?

What do you mean with "delete static variables and objects"?
You know you cannot explicitly delete objects in Java, that's why there is garbage collection. And you cannot force garbage collection to happen. The only thing you can do is make an object eligible for garbage collection by removing all references to the object. You can do this by for example setting your static reference to null:
public class Demo {
static Integer thingy = new Integer(9567412);
void demo() {
// Set thingy to null, so that the object it refers to may be garbage collected
thingy = null;
}Jesper

Can't we declare a static variable inside a memberfunction of a class?

Hi,
class A{
public void fun()
static int i=10;
can' we declare static variable in member function of class?
Thanks,

It is a common idiom in C and C++, but it is forbidden
in Java because it adds hidden dependencies.
The C way of writing a serial number generator:
int generate() {
static int n = 0;
return n++;
}Pure C has only global functions. So it needs inner
static variables to help to hide the data. I've had
lots of headaches trying to make C programs with inner
static variables work correctly because they usually
are hidden in cross-reference listings.
The Java way:
public static class SerialNumberGenerator() {
private static int n = 0;
public static int generate() {
return n++;
}The code above is as static as the C code given
before, but it tries to be more explicit (no hidden
variables).Hum... have you tried to compile your sample ?
(And anyway, what the hell would a static class be used for ???)
But perhaps you meant:
public final class SerialNumberGenerator {
   private static int n = 0;
   public static int generate() {
      return n++;

"requires unreachable" warning emitted when using static variables and the singleton pattern

I'm implementing code contracts on an existing code base and I've come across this situation in a few places. Wherever we have additional logic with code contracts where a singleton instance is instantiated, all code contracts emit a "reference use
unreached", or "requires unreachable" warning.
The code below demonstrates this.
static string instance = null;
static string InstanceGetter()
if (instance == null)
instance = "initialized";
AdditionalLogic(instance); // requires unreachable warning on this line
return instance;
static void AdditionalLogic(string str)
Contract.Requires(str != null);
Console.WriteLine(str);

Would the class get unloaded even if the Singleton object has some valid/reachable references pointing to it?
On a different note, will all the objects/instances of a class get destroyed if the class gets unloaded.That's the other way round, really: instances cannot be garbage-collected as long as they are strongly reachable (at least one reference pointing to them), and classes cannot be unloaded as long as such an instance exists.
To support tschodt's point, see the JVM specifications: http://java.sun.com/docs/books/jvms/second_edition/html/Concepts.doc.html#32202
*2.17.8 Unloading of Classes and Interfaces*
A class or interface may be unloaded if and only if its class loader is unreachable. The bootstrap class loader is always reachable; as a result, system classes may never be unloaded.
Will the same case (Custom ClassLoader getting unloaded) occur if I write the singleton using the code wherein we lazily initialize the Singleton (and actually create a Singleton instance rather than it being a Class/static variable).You should check the meaning of this vocabulary ("object", "instance", "reference"): http://download.oracle.com/javase/tutorial/java/javaOO/summaryclasses.html
The difference between the lazy vs eager initializations is the time when an instance is created. Once it is created, it will not be garbage collected as long as it is reachable.
Now I'm wondering, whether being referenced by a static attribute of a class guarantees being reachabe. I'm afraid not (see the JLS definition of reachable: http://java.sun.com/docs/books/jls/third_edition/html/execution.html#44762). That is, again, unless the class has been loaded by the system class loader.

Static and non-static variables and methods

Hi all,
There's an excellent thread that outlines very clearly the differences between static and non-static:
http://forum.java.sun.com/thread.jsp?forum=54&thread=374018
But I have to admit, that it still hasn't helped me solve my problem. There's obviously something I haven't yet grasped and if anyone could make it clear to me I would be most grateful.
Bascially, I've got a servlet that instatiates a message system (ie starts it running), or, according to the action passed to it from the form, stops the message system, queries its status (ie finds out if its actually running or not) and, from time to time, writes the message system's progress to the browser.
My skeleton code then looks like this:
public class IMS extends HttpServlet
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
        doPost(request, response);
   public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
      //get the various parameters...
         if (user.equalsIgnoreCase(username) && pass.equalsIgnoreCase(password))
            if(action.equalsIgnoreCase("start"))
                try
                    IMSRequest imsRequest = new IMSRequest();
                    imsRequest.startIMS(response);
                catch(IOException ex)
                catch(ClassNotFoundException ex)
            else if(action.equalsIgnoreCase("stop"))
                try
                    StopIMS stopIMS = new StopIMS();
                    stopIMS.stop(response);
                catch(IOException ex)
             else if(action.equalsIgnoreCase("status"))
                try
                    ViewStatus status = new ViewStatus();
                    status.view(response);
                catch(IOException ex)
         else
            response.sendRedirect ("/IMS/wrongPassword.html");
public class IMSRequest
//a whole load of other variables
public PrintWriter    out;
    public int                 messageNumber;
    public int                 n;
    public boolean         status = false; //surely this is a static variable?
    public String            messageData = ""; // and perhaps this too?
    public IMSRequest()
    public void startIMS(HttpServletResponse response) throws IOException, ClassNotFoundException
        try
            response.setContentType("text/html");
            out = response.getWriter();
            for(n = 1 ; ; n++ )
                getMessageInstance();
                File file = new File("/Users/damian/Desktop/Test/stop_IMS");
                if (n == 1 && file.exists())
                    file.delete();
                else if (file.exists())
                    throw new ServletException();
                try
                    databaseConnect();
               catch (ClassNotFoundException e)
//here I start to get compile problems, saying I can't access non-static methods from inside a static method
               out.println(FrontPage.displayHeader());
                out.println("</BODY>\n</HTML>");
                out.close();
                Thread.sleep(1000);
        catch (Exception e)
    }OK, so, specifially, my problem is this:
Do I assume that when I instantiate the object imsRequest thus;
IMSRequest imsRequest = new IMSRequest();
imsRequest.startIMS(response); I am no longer in a static method? That's what I thought. But the problem is that, in the class, IMSRequest I start to get compile problems saying that I can't access non-static variables from a static method, and so on and so on.
I know I can cheat by changing these to static variables, but there are some specific variables that just shouldn't be static. It seems that something has escaped me. Can anyone point out what it is?
Many thanks for your time and I will gladly post more code/explain my problem in more detail, if it helps you to explain it to me.
Damian

Can I just ask you one more question though?Okay, but I warn you: it's 1:00 a.m., I've been doing almost nothing but Java for about 18 hours, and I don't do servlets, so don't take any of this as gospel.
If, however, from another class (FrontPage for
example), I call ((new.IMSRequest().writeHTML) or
something like that, then I'm creating a new instance
of IMSRequest (right?)That's what new does, yes.
and therefore I am never going
to see the information I need from my original
IMSRequest instance. Am I right on this?I don't know. That's up to you. What do you do with the existing IMS request when you create the new FrontPage? Is there another reference to it somewhere? I don't know enough about your design or the goal of your software to really answer.
On the other hand, IMSRequest is designed to run
continuously (prehaps for hours), so I don't really
want to just print out a continuous stream of stuff to
the browser. How can I though, every so often, call
the status of this instance of this servlet?One possibility is to pass the existing IMSRequest to the FrontPage and have it use that one, rather than creating its own. Or is that not what you're asking? Again, I don't have enough details (or maybe just not enough functioning brain cells) to see how it all fits together.
One thing that puzzles me here: It seems to me that FP uses IMSReq, but IMSReq also uses FP. Is that the case? Those two way dependencies can make things ugly in a hurry, and are often a sign of bad design. It may be perfectly valid for what you're doing, but you may want to look at it closely and see if there's a better way.

Static variable reference.

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