Extended class variable corruption...why?
hello guys, I've beed struggling on this issue for more than 2 hours and, together with a friend, we weren't able to figure it out.
I have a class named HandlerMod that extends DefaultHandler (this one org.xml.sax.helpers.DefaultHandler)
and in this class there's a private variable named "toSet"
this variable is set with a method named toSet() and it's recalled witha method named getToSet()
the variable is correct as I can see it printing it during the process but when I use the getToSet() method the variable has the value "0.0"
I can't understand what's happening, here's some code:
this is in the HandlerMod class
public void setToSet(double value)
toSet=fatto;
System.out.println("toSet: "+toSet);//prints "4444.0"
public double getToSet()
System.out.println("toSet in getFatto is: "+toSet);//prints "4444.0"
return toSet;
}and this is in a class that extends HandlerMod
ddd = getToSet();
System.out.println("ddd �:"+ddd);//obviously prints "0.0"in other words, if the method getToSet()is used in the upper class works, if it's called in the lower class that extends HandlerMod it doesn't work and returns "0.0"
someone has an idea?
thanks
u're right, by the way this makes no difference because setToSet is called with fatto as argument, this is the code in HandlerMod
public void endDocument() throws SAXException
System.out.println("Expression � lungo: "+expression.size());
for(int i = 0; i<expression.size();i++)
System.out.println(expression.elementAt(i));
fatto = calcolaStringa();
toSend = fatto;
System.out.println("Il valore calcolato �: "+ fatto);//prints "4444.0" correctly
setToSet(fatto);
double fff = getToSet();
System.out.println("fff :"+fff);//prints "4444.0"
}the problem is that when I call the getToSet method in another class I get "0.0"
I'm a bit confused
Similar Messages
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I have two variables: windowArea and doorArea that are declared and bound in public abstract class Surface (which) implements FlatSurface (Interface). I can't use these variables in public abstract class (which) Wall extends Surface using the following code. I'm sure I have to just add a few lines of code to create instances of these variables for the Wall class - how do I do that?
Here's the code:
public interface FlatSurface {
// window, and door instances
float doorHeight = 6.75F;
int windowHeight = 4;
/** The length of the surface as measured in feet. */
double getLength();
/** Set the length of the surface as measured in feet. */
void setLength(double feet);
/** The width of the surface as measured in feet. */
double getWidth();
/** Set the width of the surface as measured in feet. */
void setWidth(double feet);
/** Calculate and return the area of the surface in square feet. */
double area();
public abstract class Surface implements FlatSurface {
* Default constructor, creates a new <code>Surface</code> instance.
public Surface () {
// Create doorArea
public static float doorArea(float setWidth) {
return setWidth * doorHeight;
// Create windowArea
public static int windowArea(int setWidth) {
return setWidth * windowHeight;
public static void main(String[] args) {
float doorWidth = 3.5F;
int windowWidth = 3;
float doorArea = (float)doorArea(doorWidth);
int windowArea = (int)windowArea(windowWidth);
System.out.println("door Area " + doorArea + " feet");
System.out.println("window Area " + windowArea + " feet");
return;
public abstract class Wall extends Surface implements Openings {
//The implementation of the Openings interface should manage windows and the door appropriately for each of the four walls
* Default constructor, creates a new <code>Surface</code> instance.
public Wall () {
//@return a <code>boolean</code> value that is true when the flat surface was added, else false.
//public boolean addOpening(FlatSurface s);
// Create northWall
public static double northWall(int setLength) {
return setLength * ceilingHeight;
// Create eastWall
public static double eastWall(int setLength) {
return setLength * ceilingHeight;
// Create southWall
public static double southWall(int setLength) {
return setLength * ceilingHeight;
// Create westWall
public static double westWall(int setLength) {
return setLength * ceilingHeight;
public static void main(String[] args) {
//Calculate Wall length
System.out.println("northWall " + (double)northWall(side1Length) - windowArea + " feet");
System.out.println("eastWall " + (double)eastWall(side2Length) - windowArea + " feet");
System.out.println("southWall " + (double)southWall(side1Length) - windowArea - windowArea + " feet");
System.out.println("eastWall " + (double)westWall(side2Length) - doorArea + " feet");
return;
}I have two variables: windowArea and doorArea that are
declared and bound in public abstract class Surface
(which) implements FlatSurface (Interface). You did not declare these variables in class Surface
(you did declare them in method main though, which restricts
their scope to this method only). Have you read the tutorial yet?
This should solve your problems. -
Assign a value to class variable
I want to define a class variable in class. And I want all subclasses of that class ot have a different value for that class variable. How can I do that?
public class BaseClass {
public static String tableName = "";
}Now if I have a ClassA and I want to assign a value like this :
public class ClassA extends BaseClass {
tableName = "location";
} I got an error message.
I can move it in a static initializer block but then it will only work when the class is loaded. In my case its possible i want to get this value without loading the class.
Ditto if i move it to constructor.
Any input? ThanksAre you saying that if i have 2 classes ClassA and
ClassB inherited from BaseClass, then both are
sharing the same copy of 'tableName' staticvariable?
If yes then I should go with an instance variable.No, I am saying that you can easily declare a
tablName in A and another tableName in B.
A.tableName will be shared between all the instances
s of A. B.tableName will be shared between all the
instances of B. And BaseClass.tableName is
irelevant. I think you try to use
BaseClass.tableName as some kind of template for
sub-classes, but this does not happen: you need to
declare tableName again and again in each subclass.
IThanks for clarifying. Each class needs to have a variable "tableName" and it needs to have one copy of this variable for all of that class's objects. 2 classes will not have the same value of this tableName variable.
Thats why I was defining it as static variable. And I define it in BaseClass so that I dont have to define it again in each subclass.
Is there any better way? Thanks -
Thread cannot access the class variables.
Hi
I have below code snippet : (Only section of which I have copied below)
public class ProcessAppendAction extends HttpServlet implements Runnable{
public ProcessAppendAction ()
MI_OS_APPEND port ;
protected void doGet(
HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
//TODO : Implement
port =
(MI_OS_APPEND) obj.getLogicalPort(
"MI_OS_APPENDPort",
MI_OS_APPEND.class);
Thread[] threads = new Thread[noOfThreads];
ProcessAppendAction run = new ProcessAppendAction(req);
Thread th = new Thread(run);
threads[no] = th;
threads[no].start();
threads[no].join();
public ProcessAppendAction(DT_REQUEST_APPEND req) {
this.requestObj = req;
// TODO Auto-generated constructor stub
public void run()
try
DT_RESPONSE res = this.port.MI_OS_APPEND(requestObj);
catch(Exception e)
int ch=0;
ch++;
} In above code I am successfully creating an object in line :
port =
(MI_OS_APPEND) obj.getLogicalPort(
"MI_OS_APPENDPort",
MI_OS_APPEND.class);But when I am trying to access this port variable in run method it is giving null.
Port in my code is a class variable.
Is it the case that thread cannot access class variable !!money321 wrote:
ok, I have removed join() from just after start().So that now the Servlet can return before the new Thread has finished. Is this what you want?
First I did invoked all threads and then in second loop i invoked Join on all threads.I don't understand. Why do you need to join() all the threads since you only start one thread in this request. What am I missing?
>
Now, my problem.
It was solved when I substituted the line
ProcessAppendAction run = new ProcessAppendAction(req)
with
ProcessAppendAction run = new ProcessAppendAction(req,port);Of course. Instance variables in Servlet instances are a no-no so passing the 'port' though an instance variable is just wrong.
>
That is passes port alongwith req while creating thread object.
But still if class variables are not thread safe, then it means if I pass object 1 to thread 1.
And then try to pass object 2 to thread 2, it might be possibility that object 1 of thread 1 might be replaced by object 2.
So, thread 1 will get an updated value object 2.Yep - that is why you should not use instance variables in Servlets and why they are not thread safe.
>
Which is not what I intend to do...:-) -
Static class variable doesn't store ?
Hi,
I'm a beginner in java.
I defined a static class variable (nodes) in th following code :
public class MySOMapp extends javax.swing.JFrame {
private static final long serialVersionUID = 1L;
private static SOMTrainer trainer;
private static SOMLattice lattice;
private static SOMNode nodes;
private static Hashtable nwordf;
public MySOMapp(String args[]) {
SOMNode nodes = new SOMNode(); //.....But a method of this class, nodes comes null. methos definition :
private void makesame() {I don't understand why the nodes is null in makesame method which is in the same class with nodes ?
thanks,
Yigit
thankyou. I solved the problem. But why static fields
are not good idea ? How can i get rid of these...Remove the static word :) Seriously, try to develop a technique to get swiftly out of the static main method. Like this:
class MyClass {
MyClass() {
// Your code here instead of in main method.
public static void main(String[] args) {
new MyClass();
}
thankyou. I solved the problem. But why static fields
are not good idea ? How can i get rid of these...Remove the static word :) Seriously, try to develop a technique to get swiftly out of the static main method. Like this:
class MyClass {
MyClass() {
// Your code here instead of in main method.
public static void main(String[] args) {
new MyClass();
}
I have two classes in same package. I defined a class variable 'no_of_gear' and later changed its value. The changed value
works in the same class but does not work in sub-class in same package.
class ClassVar {
static int no_of_gear = 5;
public static void main(String[] args) {
System.out.println(no_of_gear); //Prints 5
ClassVar cv = new ClassVar();
System.out.println(cv.no_of_gear); //Prints 5
cv.no_of_gear = 8;
System.out.println(cv.no_of_gear); //Prints 8
System.out.println(no_of_gear); //Prints 8
}Here is sub-class in same package.
class ClassVarAcc extends ClassVar {
public static void main(String[] args) {
System.out.println(no_of_gear); //Prints 5
ClassVar cv = new ClassVar();
System.out.println(cv.no_of_gear); //Prints 5
}Java Tutorial by SUN reveals that if class variable is changed by one object it is changed for all objects of that class. But, my code does not support the statement. Please, Can you clarify it?
Yes i do but not to the extent you are pointingto.
Why can't you just say you don't when you don't?
Can you answer in details?Look at your super class
class ClassVar {
static int no_of_gear = 5;
public static void main(String[] args) {
System.out.println(no_of_gear); //Prints 5
ClassVar cv = new ClassVar();
System.out.println(cv.no_of_gear); //Prints 5
cv.no_of_gear = 8;
System.out.println(cv.no_of_gear); //Prints 8
System.out.println(no_of_gear); //Prints 8
}In what method does the value of no_of_gear change?
Now look at the sub-class. Do you see yourself
calling this method?OH my dear. It is class variable that can be accessed directly (unlike instance variables) without the need of some method to change its value.
Here i change it. (Remeber: a copy of instance variable is passed to an instance of some class but no copy of class variable is passed to an instance of that class)
cv.no_of_gear = 8;
System.out.println(cv.no_of_gear); //Prints 8
Here it works fine.
System.out.println(no_of_gear); //Prints 8
But, why does not it work in sub-class?
Inherit / extend class calls constructor...
Hi,
Class A extends class B like so:
public class A extends B{}
Why is class B's constructor called? I thought when A extends
B, A gets all of B's methods and variables, great; but I don't need
the constructor called because class B has already been created. I
just want class A to inherit all of B's methods and variables. Can
a class have two constructors, so when I extend class B an empty
constructor is called but when I instantiate it the constructor
with code is called?
I feel like I’m missing something here.
Thanks,
4dplane
Yep you are missing something. :)
The constructor is just that -- it builds each instance of
the class, puts it together if you will. Without a call to the
superclass's constructor you won't get all its properties, methods,
etc.
You'll notice that the B constructor is even call first. That
is to make sure that everything is ready and accessable to A
It sounds like whatever you are trying to do isn't really a
good candidate for extension.. Fill us in a bit more and perhaps we
can come up with some ideas..
How to access the parent class variable or object in java
Hi Gurus,
I encounter an issue when try to refer to parent class variable or object instance in java.
The issue is when the child class reside in different location from the parent class as shown below.
- ClassA and ClassB are reside in xxx.oracle.apps.inv.mo.server;
- Derived is reside in xxx.oracle.apps.inv.mo.server.test;
Let say ClassA and ClassB are the base / seeded class and can not be modified. How can i refer to the variable or object instance of ClassA and ClassB inside Derived class.
package xxx.oracle.apps.inv.mo.server;
public class ClassA {
public int i=10;
package xxx.oracle.apps.inv.mo.server;
public class ClassB extends ClassA{
int i=20;
package xxx.oracle.apps.inv.mo.server.test;
import xxx.oracle.apps.inv.mo.server.ClassA;
import xxx.oracle.apps.inv.mo.server.ClassB;
public class Derived extends ClassB {
int i=30;
public Derived() {
System.out.println(this.i); // this will print 30
System.out.println(((ClassB)this).i); // error, but this will print 20 if Derived class located in the same location as ClassB
System.out.println(((ClassA)this).i); // error, but this will print 20 if Derived class located in the same location as ClassA
public static void main(String[] args) {
Derived d = new Derived();
Many thanks in advance,
Fendy
Hi ,
You cannot access the controller attribute instead create an instance of the controller class and access the attribute in the set method
OR create a static method X in the controller class and store the value in that method. and you can access the attribute by
Call method class=>X
OR if the attribute is static you can access by classname=>attribute.
Regards,
Gangadhar.S
Edited by: gangadhar rao on Mar 10, 2011 6:56 AM
How to access class variables in anonymous class??.
I have a boolean class level variable. Fom a button action , this boolean will set to true and then it used in anonymous class. In anonymous class, I am getting default value instead of true. Could u anyone help in this plzzz.
first of all, you don't want parent because that is something that Containers use to remember their containment hierarchy. you are thinking of super which is also incorrect, because that has to do with inheritance.
the problem here is a scoping problem. you generally would use final if you were accessing variables in an anonymous class that are in the local scope. in this case, you just need to create some test code and play with it. snip the code below and play with it. it shows both the given examples and some additional ways to change/display class variables.
good luck, hackerx
import javax.swing.*;
import java.awt.event.*;
public class Foo extends JPanel
private boolean the_b = true;
public static void main(String[] args)
Foo f = new Foo();
JFrame frame = new JFrame();
frame.getContentPane().add(f);
frame.pack();
frame.show();
public Foo()
// get your button
JButton b = new JButton("Not!");
b.addActionListener(new ActionListener()
public void actionPerformed(ActionEvent ae)
// *** uncomment these to play around ***
// Foo.this.the_b = false; // this will work, but unnecessary
// the_b = false; // this works fine too
notFoo();
this.add(b);
// something to show the value that accesses a class variable
// using an inner class instead of final nonsense
DisplayThread t = new DisplayThread();
t.start();
private void notFoo()
the_b = !the_b;
class DisplayThread extends Thread
public void run()
while(true)
System.err.println("boolean value: " + the_b);
try {
sleep(1000);
} catch(InterruptedException ie) {}
}
'My Application Page' is not allowed here because it does not extend class 'System.Web.UI.Page'
I have a custom SharePoint 2010 solution that includes an aspx page. The aspx page in is in the /layouts folder within the solution and I created it by just adding an application page to the solution. I am trying to create a parent-child relationship between
two different lists in SharePoint. From the parent I have a custom button on the ribbon that creates a child item with the ID of the parent stamped on it.
The page is just a processing page that forwards on parameters from the parent to the new child item. (i.e. the ID value)
The code generated when I add the aspx page is below:
<%@ Assembly Name="$SharePoint.Project.AssemblyFullName$" %>
<%@ Import Namespace="Microsoft.SharePoint.ApplicationPages" %>
<%@ Register Tagprefix="SharePoint" Namespace="Microsoft.SharePoint.WebControls" Assembly="Microsoft.SharePoint, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Register Tagprefix="Utilities" Namespace="Microsoft.SharePoint.Utilities" Assembly="Microsoft.SharePoint, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Register Tagprefix="asp" Namespace="System.Web.UI" Assembly="System.Web.Extensions, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" %>
<%@ Import Namespace="Microsoft.SharePoint" %>
<%@ Assembly Name="Microsoft.Web.CommandUI, Version=14.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="processingpage.aspx.cs" Inherits="MY.Solution.Layouts.MY.Solution.processingpage" MasterPageFile="~/_layouts/application.master" %>
<asp:Content ID="PageHead" ContentPlaceHolderID="PlaceHolderAdditionalPageHead" runat="server">
</asp:Content>
<asp:Content ID="Main" ContentPlaceHolderID="PlaceHolderMain" runat="server">
</asp:Content>
<asp:Content ID="PageTitle" ContentPlaceHolderID="PlaceHolderPageTitle" runat="server"> Processing Page </asp:Content>
<asp:Content ID="PageTitleInTitleArea" ContentPlaceHolderID="PlaceHolderPageTitleInTitleArea" runat="server" > Processing Page </asp:Content>
The code behind is as follows:
using System;
using Microsoft.SharePoint;
using Microsoft.SharePoint.Administration;
using Microsoft.SharePoint.WebControls;
using Microsoft.SharePoint.Utilities;
using System.Reflection;
namespace MY.Solution.Layouts.MY.Solution
public partial class processingpage : LayoutsPageBase
protected void Page_Load(object sender, EventArgs e)
try
//Get a reference to the SPWeb object
SPWeb oWeb = SPContext.Current.Web;
//Use the Parameters That Are Passed In
SPList thisList = oWeb.Lists[new Guid(Request.QueryString["List"])];
SPListItem thisItem = thisList.GetItemById(int.Parse(Request.QueryString["ID"]));
sContentType = thisItem["ContentType"].ToString();
sContentTypeID = thisItem.ContentTypeId.ToString();
if (sContentType == "Some Content Type")
sContentTypeID = "";
sAIID = thisItem["ID"].ToString();
//Redirect to newform.aspx with the Appropriate parameters.
Context.Response.Redirect(oWeb.Url + "/Lists/Blist" + "/NewForm.aspx?AIID=" + sAIAuditID.ToString() + "&ContentTypeId=" + sContentTypeID + "&ParentItemID" + Context.Request["ID"]);
else if (sContentType == "Some Content Type")
sContentTypeID = "";
sAIID = thisItem["AIID"].ToString();
//Redirect to newform.aspx with the Appropriate parameters.
Context.Response.Redirect(oWeb.Url + "/Lists/AList" + "/NewForm.aspx?AIID=" + sAIID.ToString() + "&ContentTypeId=" + sContentTypeID + "&ParentItemID" + Context.Request["ID"]);
else if (sContentType == "Some Content Type")
sContentTypeID = "";
sAICID = thisItem["AICID"].ToString();
//Redirect to newform.aspx with the Appropriate parameters.
Context.Response.Redirect(oWeb.Url + "/Lists/CList" + "/NewForm.aspx?AICID=" + sAICID.ToString() + "&ContentTypeId=" + sContentTypeID + "&ParentItemID" + Context.Request["ID"]);
else
LoggingService.LogError("MY.Solution - Processing Page", "No Applicable Content Type Found.");
catch (Exception ex)
LoggingService.LogError("My.Solution - Processing Page", ex.Message);
finally
//DO SOME FINAL THINGS HERE WHEN REQUIRED.
In the page I need to use Request.QueryString to get the values from the URL. But when I deploy the solution and load the page I get the error:
'MY.Solution.Layouts.MY.Solution.processingpage' is not allowed here because it does not extend class 'System.Web.UI.Page'.
When I change the line:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="processingpage.aspx.cs" Inherits="MY.Solution.Layouts.MY.Solution.processingpage" MasterPageFile="~/_layouts/application.master" %>
to inherit as follows:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="processingpage.aspx.cs" Inherits="Microsoft.SharePoint.WebControls.LayoutsPageBase" MasterPageFile="~/_layouts/application.master" %>
it does not work either.
If I change it to inherit like below:
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="processingpage.aspx.cs" Inherits="System.Web.UI.Page" MasterPageFile="~/_layouts/application.master" %>
it also does not work.
What does this error actually mean? And why doesn't the default code generated by Visual Studio work?
@NadeemYousuf I have tried this too and it didn't work.
What does the error even mean? And why does the error appear with default Visual Studio code? In my example I have just added a basic application page with no other code in it and it still does not work.
NoClassDefFoundError extending class in separate JAR
I have a class Foo which gets called from my servlet (extends HttpServlet) class. Both Foo and the servlet class are located in WEB-INF/classes and are deployed as part of the war file. Class Foo extends class Bar, which is a different .jar file located in the /WEB-INF/lib directory of the webapp. When I attempt to create an instance of Foo, I get the following exception:
java.lang.NoClassDefFoundError: /general/client/common/beans/Bar
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
at java.net.URLClassLoader.access$100(URLClassLoader.java:56)
at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1267)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1198)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
at server.DBServlet.createFoo(DBServlet.java:236)
at server.DBServlet.processInput(DBServlet.java:333)
at server.DBServlet.doGet(DBServlet.java:154)
at server.DBServlet.doPost(DBServlet.java:205)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:432)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:541)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:419)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:667)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)
I'm running this on Windows, and found if I added the classpath the the jar file where the Bar class is located, that it worked fine. But my expectation is that the jar file should have been found because it is in the /WEB-INF/lib dir. There is a line the Tomcat docs that says:
"Last, any JAR containing servlet API classes will be ignored by the classloader. All other class loaders in Tomcat 5 follow the usual delegation pattern."
So maybe I need to do something special to load the Bar class, or there's something strange about the way the classes and jars are being loaded that I don't fully understand. I was able to instantiate the Bar class directly from w/in my servlet class, I just can't create an instance of the Foo class that is in /WEB-INF/classes along with the servlet class. So I'm not convinced that the Bar class or associated jar file isn't being loaded.
I don't want to have to set the classpath explicitly, so I'm looking for advice on why I'm getting this exception and how best to dynamically load the classes I need.
Thanks.
ab.
Thanks for hanging in there so far. Here's the specifics if you want to try to re-create this.
I have a webapp, which contains the class DBServlet:
package com.hm.dhca.server;
public class DBServlet extends HttpServlet
// Stuff
public void processInput()
Foo foo = new Foo();
The webapp also contains the class Foo:
package com.hm.dhca.common;
import com.general.client.common.beans.Bar;
public class Foo extends Bar
public Foo()
super();
System.out.println("Foo");
Both of the classes are located in webapps\DHCA\WEB-INF\classes...
The Bar class is in a separate jar called HMJCommon.jar in the webapps\DHCA\WEB-INF\lib dir.
Class Bar looks like this:
package com.general.client.common.beans;
public class Bar
public Bar()
System.out.println("Bar");
DBServlet creates an instance of Foo as:
Foo foo = new Foo();
Which throws the Exception:
java.lang.NoClassDefFoundError: com/general/client/common/beans/Bar
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
at java.net.URLClassLoader.access$100(URLClassLoader.java:56)
at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1267)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1198)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
at com.hm.dhca.server.DBServlet.processInput(DBServlet.java:236)
at com.hm.dhca.server.DBServlet.doGet(DBServlet.java:154)
at com.hm.dhca.server.DBServlet.doPost(DBServlet.java:205)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:432)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:541)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.authenticator.SingleSignOn.invoke(SingleSignOn.java:419)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:667)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Thread.java:595)
Clues:
1. All three classes exist in the locations specified above - I have checked this manually.
2. Within DBServlet, I can create an instance of Bar. But I cannot create an instance of Foo without the exception.
3. If I move the Foo class from package com.hm.dhca.common to package com.hm.dhca.server (same package as DBSerlvet), everything works fine.
4. If I modify Tomcat's classpath to include the HMJCommon.jar, it works fine (as previously discussed).
Theory:
I have a vague theory that what is happening is that two different webappclassloaders are loading the Foo and Bar classes, for whatever reason. As a result, they can't see each other, because neither is up the hierarchy tree from the other.
This does not explain how I can instantiate Bar from DBServlet, but not Foo.
Hope this helps. I think I've corrected previous mistake w/ removing too much from package naming. I'm resorting to the workaround in clue #3 for the moment. But it's not the correct solution, and it's showing that I don't really understand what's going on here.
Passing Optional Parameter Via Extended Class Constructor
Following is a snippet of code I copied and have a question about when extending DataGridColumn class to sort numeric for colums that have numeric values:
CustomAdvancedDataGridColumn(columnName:String=null,numeric:Object=null)
super(columnName);
initCompare(numeric);
function initCompare(numeric:Object):void
if (numeric == NUMERIC) {
sortCompareFunction = numericCompare;
The extended class is supposed to receive variable "numeric" type Object in the constructor which is then supposed to be used in the initCompare function to determine if a column contains numeric values. This code didn't work for me as numeric variable remains null. To get it working I added a new public static const and private propery "numeric" and obtained it with get() set() to see if should the column should sort numeric. This works but you have to set the property in the extended datagrid column FLEX tag.
My question is how is the variable numeric in the code snippet above supposed to get it's new data for the initCompare function? I can't get it to be anything other than null.
Thanks for any insights...I'm new to FLEX.
Jason
Still searching for a solution.
Please note, that I'm using the syntax described in
<a href="http://help.sap.com/businessobject/product_guides/boexir31/en/xi3-1_url_reporting_opendocument_en.pdf">http://help.sap.com/businessobject/product_guides/boexir31/en/xi3-1_url_reporting_opendocument_en.pdf</a>
on page 65.
So did I get anything wrong? Help would be really appreciated, also Workarounds if there's no solution for the problem.
Private or Protected access for super class variables
What is the best practice...
Assume there is a class hierachy like
Person (Super class) / StaffMember/ Professor (Sub class)
1) The best way is to keep all the instance variables of each and every class private and access the private variables of super classes through subclass constructors (calling "super()")
Ex:-
public class Person {
private String empNo;
public Person (String empNo) {
this.empNo = empNo;
public class Professor extends Person {
private String ........;
private int ...........;
public Professor (String pEmpNo) {
super(pEmpNo);
OR
2)Changing the access level of the super class variables into "protected" or "default" and access them directly within the sub classes...
Ex:-
public class Person {
protected String empNo;
public Person () {
public class Professor extends Person {
String ........;
int ...........;
public Professor (String empNo) {
this.empNo = empNo;
Thank you...
i'd think that you'd be better off relaying your initial values through the super class's constructor that way you'll get cleaner code, there's a possibly of inconsistency with option 2. i.e. you can then write code in your super classes to generally handle and properly initialize the instance variables while in the case of option 2, you'll have arbitrary constructors performing arbitrary initialization procedures
I have noticed that class variable initialization occurs AFTER the constructor is called.
Why is this, and is this intentional?
It has caused strange behaviour in my SE java applications I am porting to MIDP.
Thanks
- Adam
Hi,
Error 1:
The problem only arises if you use the unassigned variable:
int i;
int y = i; // Use of unassigned variable here
you can just assign a value to i to solve this:
int i = 0;
int y = i; // Use of unassigned variable here
Error 2 and 3 have to do with static and non-static, not with the initialization per se. This is how it works:
static members (e.g. fields) can be accessed using this syntax: <Classname>.<FieldName>, e.g:
public static class Helpers
public static int SomeDataValue { get; set; }
class Program
static void Main(string[] args)
Helpers.SomeDataValue = 22;
On the other hand, non-static members are accessed like this: <instance>.<fieldname>. So you always need an instance of a class to access the field:
public class Order
public int OrderNumber { get; set; }
class Program
static void Main(string[] args)
Order o = new Order();
o.OrderNumber = 12;
Rgds MM
Is it save to use class variables in stateful application modules?
I've a simple question of understanding: Can I savely use class-variables in stateful application modules?
Consider the following example:
public class myStateFullAppModuleImpl extends ApplicationModuleImpl
private int myVar=0;
public int doMyWork()
myVar++;
return myVar;
Is it save to use "myVar" this way considering AM-pooling? Or should I save "myVar" in the session instead?
Thanks
Please see reply at:
Is it save to use class variables in a stateful application module?
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