Private static class

hi, what is the point of having a private static class, as you cannot acces it outside the scope of a class?

hi, what is the point of having a private static
class, as you cannot acces it outside the scope of a
class?There are lots and lots of uses. The private implementation can actually be exported outside of the outer class if implements a public interface.

Similar Messages

Attributes of private static class - private or package private?

Consider the following code:
public class Outer {
    // Remainder omitted
    private static class Nested {
        int someInt           = 10;
        String someString = "abc";
}The nested class Nested is declared private, as it is only used by the Outer class... now I wonder... should I declare Nested's attributes private oder package private... either way, they can't be accessed from the outside... any ideas?

stevops wrote:
either way, they can't be accessed from the outsideThat is true. However, when in addition the members of class Nested are declared as private, you will not be able to access them also from within the class Outer as well, i.e. int i = Nested.someInt; will give you compliation errorsAs a matter of fact, at most it'll generate some warnings, for it (the compiler) will generate synthetic accessor methods for Nested's fields.
All in all, if you plan to access private class members from an enclosing (or inner) class, you really only have two options: make them explicitly package-private, or make them implicitly so.

How to clear a private static class attribute once it's been created?

<pre>I'm working with an instance of a complex Class object that has been created using the function module HRXSS_CAT_APPLICATION_INIT. The Class object that I am trying to work with is CL_XSS_CAT_BUSINESS_LAYER and in particular its Static Private component attribute PROFILE. 
The issue that I am having is that the first call of this function module creates and populates the Static Private component attribute, PROFILE, for the instance of this Class and I do not know how to initialize it once it's been created. The PROFILE attribute is an object reference to an instance of Class CL_XSS_CAT_PROFILE. 
I want to reset/intialize this Static Private component. I can then call a Class Method with different parameters so that it repopulates PROFILE with different attributes. There is no Public method to do this in CL_XSS_CAT_BUSINESS_LAYER and even the Private method INIT_PROFILE, the logic first checks to see if the PROFILE component is initial before creating a new PROFILE object instance. All the Attributes of the CL_XSS_CAT_PROFILE object are Static and Private.
 
I would appreciate any insight anyone might have in how to reset/initialize this Class component attribute. 
Thanks much, 
 
Graham 
Sample code snippet is as follows:
 
DATA: lr_cats_application_rfc TYPE REF TO IF_XSS_CAT_APPLICATION_RFC,
lr_core TYPE REF TO IF_XSS_PT_APPLICATION_CORE,
lr_core TYPE REF TO CL_XSS_CAT_1_APPLICATION_CORE,
lr_instance TYPE REF TO CL_XSS_CAT_APPLICATION,
lr_business_layer TYPE REF TO CL_XSS_CAT_BUSINESS_LAYER,
lr_profile TYPE REF TO CL_XSS_CAT_PROFILE,
lr_profile_temp TYPE REF TO cl_xss_cat_profile.
DATA: l_employee TYPE pernr_d.
DATA: l_employee_tab TYPE rhxss_cat_employee_t.
CASE im_command.
WHEN 'DATESELECTION_PRVPERIOD'.
*-> navigate to object component reference for CL_XSS_CAT_PROFILE instance
lr_cats_application_rfc = im_ref_to_parameter_cache->REF_TO_APPLICATION.
*-> navigate to object component reference for CL_XSS_CAT_1_APPLICATION_CORE
lr_core ?= lr_cats_application_rfc->get_core( ).
*-> navigate to object component reference for CL_XSS_CAT_BUSINESS_LAYER
lr_business_layer = lr_core->business_layer.
*-> navigate to object component reference for CL_XSS_CAT_PROFILE
lr_profile = lr_business_layer->get_profile( ).
l_employee = im_ref_to_parameter_cache->pernr.
append l_employee to l_employee_tab.
 
*THIS IS WHERE I AM HAVING ISSUES...I WOULD LIKE TO CLEAR/INITIALIZE THE STATIC PRIVATE COMPONENT LR_BUSINESS_LAYER->PROFILE BEFORE CALLING THE METHOD INITIALIZE_FOR_TIME_RECORDING 
 
 *THE FOLLOWING LINE FAILS ON A SYNTAX CHECK WITH 'FIELD "PROFILE" IS UNKNOWN. IT IS NEITHER IN ONE OF THE *SPECIFIED TABLES NOR DEFINED BY A "DATA" STATEMENT
 
clear: lr_business_layer->profile.
CALL METHOD lr_business_layer->initialize_for_time_recording
EXPORTING
im_employee_tab = l_employee_tab
im_profile_id = 'MODAPPR1'
im_startdate = sy-datum
EXCEPTIONS
pernr_not_enqueued = 1
no_pernr_for_user_found = 2
profile_not_found = 3.</pre>
Edited by: Matt on Aug 1, 2009 12:44 PM

OK...I apologize but I did not dig deep enough to see that the Enhancement Framework allows for the addition of Methods to Classes/Interfaces. Most of this ABAP OO stuff is still quite new to me so I'm struggling with syntax and what is and isn't possible based on how everything is declared. I guess now that I know I can do this I am having some problems understanding how singleton Class objects work and how to 'reset' them.
The Class instance based on CL_XSS_CAT_BUSINESS_LAYER has a Static Private attribute PROFILE that is an object reference to the singleton Class instance CL_XSS_CAT_PROFILE.
The singleton Class instance of CL_XSS_CAT_PROFILE has all of its attributes set to Static Private. If you look at this Class in SE80 you see that one of its attributes is also called PROFILE and is an object reference variable to itself.
So the issue I am having is how to go about 'initializing' this singleton object so that I can 'recreate' this singleton object using a copy of the existing S
I used the enhancement framework to create a copy of the CL_XSS_CAT_BUSINESS_PROFILE Instance Private Method INIT_PROFILE , called in INIT_PROFILE2, but I am not sure how to 'clear/reset' the instance of the CL_XSS_CAT_PROFILE object.
Since PROFILE is an attribute of the CL_XSS_BUSINESS_LAYER object, I thought that a simple CLEAR PROFILE would reset the object but this is not the case. Within this method the FREE clears the value of the reference variable PROFILE but as soon as you step into the method me->init_profile, the value of PROFILE goes back to what it was. I need for all of the CL_XSS_CAT_PROFILE instance attributes to be reset or initialized so I can fill them again. I think I'm getting confused on the scope of things...should I be enhancing the CL_XSS_CAT_PROFILE Class with 'setter' methods so I can initialize all of the Static Private attributes that way instead of trying to clear all the attributes at a higher call level?
Any assistance with helping me with my thought process or approach to this would be much appreciated.
METHOD INIT_PROFILE2.
FREE PROFILE. >>> is reset but it does not carry through to next method call and does not clear all the attributes of the object referenced in PROFILE
CALL METHOD me->init_profile
EXPORTING
IM_PROFILE_ID = im_profile_id
etc...

Private static nested class

Hi everyone,
I'm practicing nested classes. I've written this simple class:
public class OuterClass {
private static class InnerClass {
     private InnerClass() {
        System.out.println("in constructor" }
} and another simple class to test:
public class TestClass {
public static void main(String[] args) {
        OuterClass.InnerClass in=   new OuterClass.InnerClass();
}All classes compile and main method runs with no problem. Now I wonder what is the meaning of the private modifier here ??
Thanks

Ok, I'm using Oracle's JDeveloper 3.2 ( jdk1.2.2). The code I posted compiles and runs with no errors in Jdeveloper.
However, I tested this on the command line ( using javac directly ) and it does not compile !

Compiler bug with generics and private inner classes

There appears to be a bug in the sun java compiler. This problem was reported against eclipse and the developers their concluded that it must be a problem with javac.
Idea also seems to compile the example below. I couldn't find a bug report in the sun bug database. Can somebody tell me if this is a bug in javac and if there is a bug report for it.
https://bugs.eclipse.org/bugs/show_bug.cgi?id=185422
public class Foo <T>{
private T myT;
public T getT() {
return myT;
public void setT(T aT) {
myT = aT;
public class Bar extends Foo<Bar.Baz> {
public static void main(String[] args) {
Bar myBar = new Bar();
myBar.setT(new Baz());
System.out.println(myBar.getT().toString());
private static class Baz {
@Override
public String toString() {
return "Baz";
Eclipse compiles and runs the code even though the Baz inner class is private.
javac reports:
Bar.java:1: Bar.Baz has private access in Bar
public class Bar extends Foo<Bar.Baz>
^
1 error

As I said in my original post its not just eclipse that thinks the code snippet is compilable. IntelliJ Idea also parses it without complaining. I haven't looked at the java language spec but intuitively I see no reason why the code should not compile. I don't think eclipse submitting bug reports to sun has anything to do with courage. I would guess they just couldn't be bothered.

Private static MyInnerClass extends OtherClass + protected methods

Hi!
Consider this case:
public class A {
private static class A1 extends B {
// this would resolve the error:
//       protected static void b() { B.b(); }
void a() { A1.b(); } // ERROR: B.b() is inaccessible
public class B {
protected static void b() {}
}(Where A and B are in different packages.)
Why is B.b() inaccessible here?
A1 extends B, so it sees its protected methods.
A is a nesting class of A1, so it sees the protected methods of A1.
What am I missing here?
Thank you!
Agoston

OK, my mistake, I missed the part about different
packages.
However the following further inner class of A
compiles for me:
     private static class A2 extends A1
          A2()
               b();
               A1.b();
     }using the OP's original code without A1.b().That's what I was talking about: b() can be called from children, but not from the nesting class.
>
The statement quoted from the JCP exam is not
correct. The inherited protected member is available
to subclasses of A1, so the protected member
b() doesn't 'become private' at all. It stays as is
was, i.e. protected, i.e. accessible within the
original package or to subclasses.If it stays protected, why can't the nesting class see it? (Once again, a protected method defined in A1 and not inherited from B is visible from A.)
It seems as if the inherited protected method teleports into some mysterious realm of visibility levels between private and protected. (I.e. it's like protected, only from a nesting class it's seen as super-private - since the nesting class should even be able to see the private methods of its inner class, shouldn't it?)
This whole inconsequent behavior on the part of the compiler feels like a huge bug to me.
Nothing changes.Unfortunately. :)
Agoston

Static class member is beying destroyed inside a Controller - Why?

Hello,
I need to manage a certain BigDecimal class member in a Dynpro application which will not be destroyed. This class member represents a key in a database which from few reasons I would like to manage on my own.
In order to implement that, I have created a private static class member at the Controller and a get method in order for the other views to get it's value.
The get method checks if the value is null.
In case it is it queries the Database for the maximum value and return it + 1 to the requestor.
In case it is not null it simply increments the current value by 1 and returns it to the requestor.
According to my assumption, a DB query should happen only once since this member is static, yet when I monitor the application I see it queries the Database occasionally, which mean that the member has been destroyed.
I tried solving that by setting the expirationTime of the application to few hours but even inside this range the variable is being destroyed.
My questions are:
1. What am I missing here?
2. How and where should I manage a static variable in a Web dynpro application in order to assure it won't be destroyed during the lifetime of the application?

Hello Valery,
Here is the relevant code:
At the controller I declare this static member:
private static BigDecimal globalRequest = null;
And here is the method:
public java.lang.String getNewRequestNumber( java.sql.Statement statement )
    //@@begin getNewRequestNumber()
    try
          if (globalRequest == null)
               ResultSet rs = statement.executeQuery("SELECT MAX(record_number) AS maxRecord FROM COMMITTEES_REQUEST");
               if (rs.next())
                    BigDecimal maxRequest = rs.getBigDecimal("maxRecord");
                    globalRequest = maxRequest.add(new BigDecimal(1));
                    rs.close();
                    return (globalRequest.toString());
               else
                    rs.close();
                    return null;
          else
               globalRequest = globalRequest.add(new BigDecimal(1));
               return (globalRequest.toString());
    catch (SQLException e)
         return null;
    //@@end
Thank you in advance,
Roy

Private static ArrayList within java.util.Arrays

I was recently reviewing the code in java.util.Arrays (class version 1.45 - Java version 1.4.1). Beginning on line 2289 is a private static class named ArrayList. I'm completely baffled as to why the author created this slimmed-down private class (which would be, incidentally, returned by the Arrays.asList(Object[] a) method) rather than use the public class java.util.ArrayList. Can anyone offer an explanation?
Thanks,
John

from JDK JAVADoc:
asList
public static List asList(Object[] a)
Returns a fixed-size list backed by the specified array. (Changes to the returned list "write through" to the array.) This method acts as bridge between array-based and collection-based APIs, in combination with Collection.toArray. The returned list is serializable.
So the private ArrayList extends java.util.ArrayList, and any changes made this list does not affect the internal Object[].... in other words can not be changed.

Creation of a static class with private methods

I'm new to java programming and am working on a project where I need to have a static class that does a postage calculation that must contain 2 private methods, one for first class and one for priority mail. I can't seem to figure out how to get the weight into the class to do the calculations or how to call the two private methods so that when one of my other classes calls on this class, it retrieves the correct postage. I've got all my other classes working correct and retrieving the information required. I need to use the weight from another class and return a "double". Help!!!
Here's my code:
* Title: Order Control 
* Description: Order Control Calculator using methods and classes
* Copyright: Copyright (c) 2002
* Company: Info 250, sec 001, T/TH 0930
* @author Peggy Blake
* @version 1.0, 10/29/02
import javax.swing.*;
public class ShippingCalculator
static double firstClass, priorityMail;
//how do I get my weight from another class into this method to use??? not sure I understand how it works.
public static double ShippingCalculator(double weight)
String responseFirstClass;
double quantity, shippingCost;
double totalFirstClass, firstClass, priorityMail, totalShipping;
double priorityMail1 = 3.50d;//prioritymail fee up to 1 pound
double priorityMail2 = 3.95d;//prioritymail fee up to 2 pounds
double priorityMail3 = 5.20d;//prioritymail fee up to 3 pounds
double priorityMail4 = 6.45d;//prioritymail fee up to 4 pounds
double priorityMail5 = 7.70d;//prioritymail fee up to 5 pounds
quantity = 0d;//ititialization of quantity
// weight = 0d;//initialization of weight
// shippingCost = 0d;
//calculation of the number of items ordered..each item weights .75 ounces
quantity = (weight/.75);
if (quantity <= 30d)
//add 1 ounce to quantities that weigh less than 30 ounces
weight = (weight + 1);
else
//add 2 ounces to quantities that weigh more than 30 ounces
weight = (weight + 2);
if (weight > 80d)
//message to orderclerk ..order over 5 lbs, cannot process
JOptionPane.showMessageDialog(null, "Order exceeded 5 lbs, cannot process");
//exit system, do not process anything else
System.exit (0);
else
if (weight < 14d)
//send message to customer: ship firstclass or priority, y or n
responseFirstClass = JOptionPane.showInputDialog(null, "Ship first class? y or n?");
if (responseFirstClass.equals("y"))
//compute FirstClass shipping cost
totalFirstClass = ((weight - 1) * .23d) + .34d;
firstClass = totalFirstClass;
else
//compute PriorityMail cost for orders less than 14 ounces
priorityMail = (priorityMail1);
else
if (weight <=16d)
//compute totalshipping for orders up to 16 ounces
priorityMail = (priorityMail1);
else
if (weight <=32d)
//compute totalshipping for orders up to 32 ounces
priorityMail = (priorityMail2);
else
if (weight <=48d)
//compute totalshipping for orders up to 48 ounces
priorityMail = (priorityMail3);
else
if (weight <= 64d)
//compute totalshipping for orders up to 64 ounces
priorityMail = (priorityMail4);
else
//compute totalshipping for orders up to 80 ounces
priorityMail = (priorityMail5);
priorityMail = 0d;
firstClass = 0d;
firstClassMail ();
priorityMailCost ();
//I think this is where I should be pulling the two methods below into my code, but can't figure out how to do it.
shippingCost = priorityMail + firstClass;
return (shippingCost);
}//end method calculate shipping
private static double firstClassMail()//method to get first class ship cost
return (firstClass);
}//end method firstclass shipping
private static double priorityMailCost()//method to get priority mail cost
return (priorityMail);
}//end method priorityMail
}//end class shipping calculator

public class A {
public String getXXX () {
public class B {
A a = new A();
public void init () {
a.getXXX();
}

Private inner class and static private inner

Hi,
I understand the concept and usage of inner classes in general.
When should we go for a private inner class and when for a static private inner class? I tried searching but it wasn't of much help.
Basically I need to design a caching solution in which I need to timestamp the data object. After timestamping, data will be stored in a HashMap or some other collection. I'm planning to use a wrapper class (which is inner and private) which holds the data object and timestamp. I can make the program work by using either normal inner class or static inner class, however would like to know which is better in such case. Also If I can get some general guidelines as to when to use a staic inner class and when to use a normal inner class, it would help me.
Thanks in advance.

user1995721 wrote:
When should we go for a private inner class and when for a static private inner class?
I can make the program work by using either normal inner class or static inner class, however would like to know which is better
If I can get some general guidelines as to when to use a static inner class and when to use a normal inner class, it would help me.Making the inner class static is helpful in that it limits visibility.
If the inner class needs to access non-static fields or methods from the containing class instance
the inner class has to be non-static.

Are private fields public in a static class?

If a variable in a static class is declared as private, it still seems to be visible. Are access specifiers without any importance in a static class?

Roxxor wrote:
tschodt wrote:
The outer class can access all the fields of the nested class, yes.Yes, but only if the nested class is static, otherwise not.
This is what I have noticed:
If the nested class is not static, then the outer class has to instantiate the nested class to access its variables. Well, not really. If the nested class is not static (i.e., it's a nested class), then its variables don't even exist until an instance is created.
If the nested class is not static, then the nested class can access the outer class´ variables without instantiate it. The inner class can only exist if there exists an instance of the outer class. An inner class (a non-static nested class) contains a reference to the wrapping class. So, it doesn't have to instantiate the outer class, because an instance already exists.
If the nested class is static, then the nested class has to instantiate the outer class to access its variables. I guess. It seems like a really strange design though.

Why do we need private static method or member class

Dear java gurus,
I have a question about the use of private and static key words together in a method or inner class.
If we want to hide the method, private is enough. a private static method is sure not intended to be called outside the class. So the only usage I could see is that this private static method is to be called by another static method. For inner class, I see the definition of Entry inner class in java.util.Hashtable, it is static private. I don't know why not just define it as private. Could the static key word do anything better.
Could anybody help me to clear this.
Thanks,

What don't you get? Private does one thing, andstatic does >something completely different.
If you want to listen to music, installing an airconditioner doesn't help>
Hi, if the private keyword is the airconditioner, do
you think you could get music from the static keyword
(it acts as the CD player) in the following codes:You're making no sense and you're trying to stretch the analogy too far.
Private does one thing. If you want that thing, use private.
Static does something completely different and unrelated. If you want that thing, use static.
If you want both things, use private static.
What do you not understand? How can you claim that you understand that they are different, and then ask, "Why do we need static if we have private"? That question makes no sense if you actually do understand that they're different.

Alternative to Static Class Inherit

Greetings,
I’ve been using some code for years in a different number of applications but that involves a lot of copy paste and is a nightmare to maintain. For that reason I’ve took some time to re-organize some of my codes and that mainly involves
splitting it into multiple projects for latter inclusion in a number of solutions.
So far so good and I’d say 95% is done but I’m now stuck with a Static Class I need to use. I basically need a few “Global” parameters and settings to be available across every solution. I know I can’t Inherit a Static Class nor override
a Field to return a different value unfortunately.
In a nutshell:
myFrameworkProject
namespace
myFramework.Classes{
 //these contains general stuff
used in every project
 public static class Globals{
 public static
XPTO veryImportantProperty = new XPTO()
 public static
Settings Settings = new Settings();
public void doSomethingImportant();
Public class Settings{
 Private
string Username;
 Private
string Password;
 Private
string Whatever;
myFancyProject
namespace
myFancyProject.Classes{
 //these add specific stuff used
in this project
 public static class Globals : myFramework.Classes.
Globals {
 public static
override mySettings Settings = new mySettings();
Public class mySettings: myFramework.Classes .Settings{
 //some
more specific settings I need
 Private
string SomethingElse;
What are my options? I’ve been trying to play with Singletons but for some reason I just can’t seem to make it work the way I want to…probably because it’s just not the right way to do it in the first place.

I think you are over thinking it a little bit. The example you have above would be great if you had multiple setting types you wanted to retrieve within the same application domain instance using keys or specific types. The way I understand your problem
is you have one settings type per application that you run with various applications sharing a code base. Here is an example I created for you which better illustrates the solution I had in mind when I read your problem.
There are 2 namespaces, the one for your custom project(s) named FancyProject and then the Core / framework. Hope this helps!
namespace JF.FancyProject
using JF.Framework.Classes;
// in initialization of your default application domain (ie. in your application startup)
// inject your MySingleton with your custom implementation of ISettingsBuilder
// this can be done in many ways from hard coding in each startup routine to IoC / Dependency Injection
// the end result is this
public static class Console
public static void Main(params string[] args)
MySingleton.Initialize(new ConcreteSettingsBuilder());
// now you can use it where ever
var temp = MySingleton.SettingsConcreteInstance<ConcreteSettings>().SomethingCustom;
// or base
var temp1 = MySingleton.SettingsInstance.SomeBaseThing;
public sealed class ConcreteSettings : JF.Framework.Classes.SettingsBase
public string SomethingCustom { get; set; }
public sealed class ConcreteSettingsBuilder : BaseSettingsBuilder, ISettingsBuilder
public override SettingsBase CreateSettings()
var settings = new ConcreteSettings();
// call the base if you need to get standard settings populated
base.populateBaseSettings(settings);
// populate all of your custom settings
return settings;
namespace JF.Framework.Classes
public abstract class SettingsBase
public string SomeBaseThing { get; set; }
// base settings and behavior that can be abstracted
public static class MySingleton
private static SettingsBase _settings;
private static Lazy<SettingsBase> _lazyCreationMethod;
public static void Initialize(ISettingsBuilder builder)
_lazyCreationMethod = new Lazy<SettingsBase>(builder.CreateSettings);
public static SettingsBase SettingsInstance
get { return _lazyCreationMethod.Value; }
public static T SettingsConcreteInstance<T>() where T : SettingsBase
return (T) _lazyCreationMethod.Value;
public abstract class BaseSettingsBuilder : ISettingsBuilder
public abstract SettingsBase CreateSettings();
protected virtual void populateBaseSettings(SettingsBase settings)
// if you find many of your settings are created the same way use a base class
public interface ISettingsBuilder
SettingsBase CreateSettings();
Edit:
One more thought. I do agree with some of the other posters that for bigger projects the use of a Singleton pattern is not a good idea. For little applications it does not matter too much because chances are there is not enough substance that it will
hinder your code and the development cycles are generally very short.
Should you want to reconsider the Singleton pattern then I recommend you look at something like
Autofac, you could use this to inject instances of your ISettingsBuilder, or other concrete instances, directly into your dependent classes and you could take it further in developing self containing services that you could
inject as well.
Again, for small projects its not a big deal but if you ever start on something a bit more complex its worth looking into.
-Igor

NullPointer Exception ,web start Static class loading in sun JRE with JNLP

I have a netbenas based application and using with jre 1.6.0_22.
i am getting NPE as
java.lang.NullPointerException
at com.sun.deploy.security.CPCallbackHandler.isAuthenticated(Unknown Source)
at com.sun.deploy.security.CPCallbackHandler.access$1300(Unknown Source)
at com.sun.deploy.security.CPCallbackHandler$ChildElement.checkResource(Unknown Source)
at com.sun.deploy.security.DeployURLClassPath$JarLoader.checkResource(Unknown Source)
at com.sun.deploy.security.DeployURLClassPath$JarLoader.getResource(Unknown Source)
at com.sun.deploy.security.DeployURLClassPath.getResource(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at com.sun.jnlp.JNLPClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at com.osi.solutions.platform.classbuilder.view.ClassExplorerTopComponent.<init>(ClassExplorerTopComponent.java:89)
at com.osi.solutions.platform.classbuilder.view.ClassExplorerTopComponent.getDefault(ClassExplorerTopComponent.java:143)
at com.osi.solutions.platform.classbuilder.view.ClassExplorerTopComponent$ResolvableHelper.readResolve(ClassExplorerTopComponent.java:198)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at java.io.ObjectStreamClass.invokeReadResolve(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at org.netbeans.modules.settings.convertors.XMLSettingsSupport$SettingsRecognizer.readSerial(XMLSettingsSupport.java:544)
at org.netbeans.modules.settings.convertors.XMLSettingsSupport$SettingsRecognizer.instanceCreate(XMLSettingsSupport.java:576)
at org.netbeans.modules.settings.convertors.SerialDataConvertor$SettingsInstance.instanceCreate(SerialDataConvertor.java:420)
at org.netbeans.core.windows.persistence.PersistenceManager.getTopComponentPersistentForID(PersistenceManager.java:531)
at org.netbeans.core.windows.persistence.PersistenceManager.getTopComponentForID(PersistenceManager.java:641)
at org.netbeans.core.windows.PersistenceHandler.getTopComponentForID(PersistenceHandler.java:422)
at org.netbeans.core.windows.PersistenceHandler.load(PersistenceHandler.java:147)
at org.netbeans.core.windows.WindowSystemImpl.load(WindowSystemImpl.java:69)
[catch] at org.netbeans.core.NonGui$2.run(NonGui.java:178)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at org.netbeans.core.TimableEventQueue.dispatchEvent(TimableEventQueue.java:104)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
This issue comes very occassionaly .
Does someone have any idea what is wrong. Is this related to any jre bug.
Thanks,
totaram

Hi I'm the one who posted those findings... though further investigation found that increasing your heap size can help, but at best it only reduces the occurances of the problem.
The real cause of the issue is that the Signer's info for a CachedJarFile is held onto by softreferences and is not "rebuilt" if it has been garbage collected. the Reason that increasing your initial heap size works, is that it helps to delay the conditions on which these softreferences are garbage collected. (SoftReferences become eligible for garbage collection when the heap needs to be expanded)
I've put together a hack that traverses all of the jars in a webstart application, finds their corresponding CachedJarFile instance and sticks all of the relevant SoftReferences into a static list, so that they become "hard references" and are never garbage collected.
Below is my JarSignersHardLinker.java hack To use it, just call JarSignersHardLinker.go() it will then
* Check that you are running on webstart and you are on java 1.6 update 19 or higher.
* If the above is true then it will spawn a new thread and create hard links to all the jarsigners for each jar on the classpath.
If you need more info email me on my gmail account. My user name is squaat. I've also posted this code at Re: Error with Java WebStart Signed Jars on 1.6.0_19's new Mixed Code
If you find this helpful and it solves your problems, please leave a positive comment and/or vote for the bug at:
http://bugs.sun.com/view_bug.do?bug_id=6967414
If any oracle/sun webstart engineers are reading this, please contact me... we'd really like this bug fixed.
import java.io.IOException;
import java.lang.ref.SoftReference;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.jar.JarFile;
* A utility class for working around the java webstart jar signing/security bug
* see http://bugs.sun.com/view_bug.do?bug_id=6967414 and http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6805618
* @author Scott Chan
public class JarSignersHardLinker {
 private static final String JRE_1_6_0 = "1.6.0_";
 * the 1.6.0 update where this problem first occurred
 private static final int PROBLEM_JRE_UPDATE = 19;
 public static final List sm_hardRefs = new ArrayList();
 protected static void makeHardSignersRef(JarFile jar) throws java.io.IOException {
 System.out.println("Making hard refs for: " + jar );
 if(jar != null && jar.getClass().getName().equals("com.sun.deploy.cache.CachedJarFile")) {
 //lets attempt to get at the each of the soft links.
 //first neet to call the relevant no-arg method to ensure that the soft ref is populated
 //then we access the private member, resolve the softlink and throw it in a static list.
 callNoArgMethod("getSigners", jar);
 makeHardLink("signersRef", jar);
 callNoArgMethod("getSignerMap", jar);
 makeHardLink("signerMapRef", jar);
// callNoArgMethod("getCodeSources", jar);
// makeHardLink("codeSourcesRef", jar);
 callNoArgMethod("getCodeSourceCache", jar);
 makeHardLink("codeSourceCacheRef", jar);
 * if the specified field for the given instance is a Softreference
 * That soft reference is resolved and the returned ref is stored in a static list,
 * making it a hard link that should never be garbage collected
 * @param fieldName
 * @param instance
 private static void makeHardLink(String fieldName, Object instance) {
 System.out.println("attempting hard ref to " + instance.getClass().getName() + "." + fieldName);
 try {
 Field signersRef = instance.getClass().getDeclaredField(fieldName);
 signersRef.setAccessible(true);
 Object o = signersRef.get(instance);
 if(o instanceof SoftReference) {
 SoftReference r = (SoftReference) o;
 Object o2 = r.get();
 sm_hardRefs.add(o2);
 } else {
 System.out.println("noooo!");
 } catch (NoSuchFieldException e) {
 e.printStackTrace();
 return;
 } catch (IllegalAccessException e) {
 e.printStackTrace();
 * Call the given no-arg method on the given instance
 * @param methodName
 * @param instance
 private static void callNoArgMethod(String methodName, Object instance) {
 System.out.println("calling noarg method hard ref to " + instance.getClass().getName() + "." + methodName + "()");
 try {
 Method m = instance.getClass().getDeclaredMethod(methodName);
 m.setAccessible(true);
 m.invoke(instance);
 } catch (SecurityException e1) {
 e1.printStackTrace();
 } catch (NoSuchMethodException e1) {
 e1.printStackTrace();
 } catch (IllegalArgumentException e) {
 e.printStackTrace();
 } catch (IllegalAccessException e) {
 e.printStackTrace();
 } catch (InvocationTargetException e) {
 e.printStackTrace();
 * is the preloader enabled. ie: will the preloader run in the current environment
 * @return
 public static boolean isHardLinkerEnabled() {
 boolean isHardLinkerDisabled = false; //change this to use whatever mechanism you use to enable or disable the preloader
 return !isHardLinkerDisabled && isRunningOnJre1_6_0_19OrHigher() && isRunningOnWebstart();
 * is the application currently running on webstart
 * detect the presence of a JNLPclassloader
 * @return
 public static boolean isRunningOnWebstart() {
 ClassLoader cl = Thread.currentThread().getContextClassLoader();
 while(cl != null) {
 if(cl.getClass().getName().equals("com.sun.jnlp.JNLPClassLoader")) {
 return true;
 cl = cl.getParent();
 return false;
 * Is the JRE 1.6.0_19 or higher?
 * @return
 public static boolean isRunningOnJre1_6_0_19OrHigher() {
 String javaVersion = System.getProperty("java.version");
 if(javaVersion.startsWith(JRE_1_6_0)) {
 //then lets figure out what update we are on
 String updateStr = javaVersion.substring(JRE_1_6_0.length());
 try {
 return Integer.parseInt(updateStr) >= PROBLEM_JRE_UPDATE;
 } catch (NumberFormatException e) {
 //then unable to determine updatedate level
 return false;
 //all other cases
 return false;
 * get all the JarFile objects for all of the jars in the classpath
 * @return
 public static Set<JarFile> getAllJarsFilesInClassPath() {
 Set<JarFile> jars = new LinkedHashSet<JarFile> ();
 for (URL url : getAllJarUrls()) {
 try {
 jars.add(getJarFile(url));
 } catch(IOException e) {
 System.out.println("unable to retrieve jar at URL: " + url);
 return jars;
 * Returns set of URLS for the jars in the classpath.
 * URLS will have the protocol of jar eg: jar:http://HOST/PATH/JARNAME.jar!/META-INF/MANIFEST.MF
 static Set<URL> getAllJarUrls() {
 try {
 Set<URL> urls = new LinkedHashSet<URL>();
 Enumeration<URL> mfUrls = Thread.currentThread().getContextClassLoader().getResources("META-INF/MANIFEST.MF");
 while(mfUrls.hasMoreElements()) {
 URL jarUrl = mfUrls.nextElement();
// System.out.println(jarUrl);
 if(!jarUrl.getProtocol().equals("jar")) continue;
 urls.add(jarUrl);
 return urls;
 } catch(IOException e) {
 throw new RuntimeException(e);
 * get the jarFile object for the given url
 * @param jarUrl
 * @return
 * @throws IOException
 public static JarFile getJarFile(URL jarUrl) throws IOException {
 URLConnection urlConnnection = jarUrl.openConnection();
 if(urlConnnection instanceof JarURLConnection) {
 // Using a JarURLConnection will load the JAR from the cache when using Webstart 1.6
 // In Webstart 1.5, the URL will point to the cached JAR on the local filesystem
 JarURLConnection jcon = (JarURLConnection) urlConnnection;
 return jcon.getJarFile();
 } else {
 throw new AssertionError("Expected JarURLConnection");
 * Spawn a new thread to run through each jar in the classpath and create a hardlink
 * to the jars softly referenced signers infomation.
 public static void go() {
 if(!isHardLinkerEnabled()) {
 return;
 System.out.println("Starting Resource Preloader Hardlinker");
 Thread t = new Thread(new Runnable() {
 public void run() {
 try {
 Set<JarFile> jars = getAllJarsFilesInClassPath();
 for (JarFile jar : jars) {
 makeHardSignersRef(jar);
 } catch (Exception e) {
 System.out.println("Problem preloading resources");
 e.printStackTrace();
 } catch (Error e) {
 System.out.println("Error preloading resources");
 e.printStackTrace();
 t.start();
}Edited by: 855200 on 04-Jul-2011 17:31

Static class reference

Below we have a class containing a static class variable and a static accessor method.
The method is responsible for assigning the variable, which it does on demand.
public class MyClass
 private static int INFO = -1;
 public static int getInfo()
 if(INFO < 0)
 try
 INFO = ...;
 catch(Exception e)
 return INFO;
 }When using this class is it not safe to assume that the assignment of the variable will ever only occur once for the life of the system that uses this class? (afterall is it static within the class)
I am experiencing the situation whereby EVERY time the method is called, the assignment of the variable is necessary. I can only assume that the static instance of this class in memory has been lost between each call and therefore the state/value of the variable has also been lost.
It is worth noting that no object instances of this class are ever created. The class is accessed only through its static interface. It seems that since no local reference to objects of this class are held in memory then the entire class, along with its internal static state, is cleared from memory (garbage collected?).
How is it possible to ensure that the state of static fields within such a class is preserved over time, without create instances of the class.
John

When using this class is it not safe to assume that
the assignment of the variable will ever only occur
once for the life of the system that uses this class?First of all, you haven't said what you assign it to, so we can't say. If you assign a value less than zero then it will be reassigned next time the method is called.
Secondly, it depends on whether or not you're expecting it to be thread-safe? It isn't.
If your code is not multi-threaded, then the section of code in your getInfo method that assigns the field should only execute once during a single run of an application.
Thirdly, you explicitly assign it (to minus one) at class initialisation time, so stricty speaking, the variale will always be assigned at least once, and will be assigned at least once more if the getInfo method is ever called.
I am experiencing the situation whereby EVERY time the
method is called, the assignment of the variable is
necessary. Can you offer any evidence to this? A small, complete, compilable and executable example that demonstrates the problem will help, and will probably get you an answer pretty quickly around here.
I can only assume that the static instance
of this class in memory has been lost between each
call and therefore the state/value of the variable has
also been lost.Then either there is a bug in your JVM, or at least two versions of the class have been loaded, and at least one of those was not loaded by the system classloader. Without further info, we aren't going to be able to help much more here.
The class is accessed only
through its static interface. It seems that since no
local reference to objects of this class are held in
memory then the entire class, along with its internal
static state, is cleared from memory (garbage
collected?).This is not allowed under the JLS if the class was loaded by the system classloader. If it was loaded by another classloader, then it is only allowed if it can be determined that the class will never again be used throughout the entire run of the application. Since you are referencing the class again, this should not be happening.
How is it possible to ensure that the state of static
fields within such a class is preserved over time,
without create instances of the class.From what you have told us so far, it should be. You will probably have to provide some code for us to help you further.

Private static class

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