Static and non-static variables and methods

Question

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

Answer 1

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.