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From "Mauro Manfrin (JIRA)" <j...@apache.org>
Subject [jira] Commented: (ECS-1) addElement(Element element) methods can fail
Date Thu, 03 Jul 2008 10:46:44 GMT

    [ https://issues.apache.org/jira/browse/ECS-1?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12610191#action_12610191

Mauro Manfrin commented on ECS-1:

Ok, you're right! I'm wrong.

I work on these issue some months ago, and so I forgot these details.
I commented out those lines to avoid confusion, but for binary compatibility that is a problem,
I know.

I have 2 solutions:
1) changing the semantics for the keys enumeration; that enumeration will enumerate only "explictly
given" keys (someone really used that enumeration?) 
2) reimplementing a new keys() method (and also deprecating it) to construct an enumeration
of objects in registryList, inventing a new key for all those elements without an "explicitly
given name" (elements not in registry). The new name is something like #@HcAg@#454545 where
454545 is the hascode for the object.
Then, perfecting registry access methods to recognize those names, and looking excplicitly
in registryList for objects with the correct hashcode.
This new implementation of keys() should guarantee binary compatibility, and deprecation of
that method will prevent hascode complex accesses and hascode issues.

For the second solution, I'll attach "secondConcreteElement.zip" with the ConcreteElement.java
class and ConcreteElement.patch (created with NetBeansSvn...hope it works).

That seems to work good; here you have a little test that fills a registry and then empties
that registry:

public static void main(String[] ss) {
        Div d=new Div();
        d.addElementToRegistry(new BR());
        P p=new P();
        d.addElementToRegistry(new Div());
        d.addElementToRegistry("string content");
        Enumeration e=d.keys();
        while (e.hasMoreElements()) {
            String  s=(String)e.nextElement();

What do you think?


> addElement(Element element) methods can fail
> --------------------------------------------
>                 Key: ECS-1
>                 URL: https://issues.apache.org/jira/browse/ECS-1
>             Project: ECS
>          Issue Type: Bug
>         Environment: in Ibm Virtual Machines, but probabily also in Sun Virtual Machines
>            Reporter: Mauro Manfrin
>            Assignee: Robert Burrell Donkin
>            Priority: Critical
>         Attachments: ecs-maintrunk-patches.zip
> The class ConcreteElement exposes a method
> addElement(Element element)
> that calls
> addElementToRegistry(Integer.toString(element.hashCode()),element);
> so it gives a key valued element.hashCode() to that element.
> That's the point: element.hashCode() can't be a unique key because sometimes we can have
two elements with the same hasocode.
> javadoc states:
> "It is not required that if two objects are unequal according to the 
> equals(java.lang.Object) method, then calling the hashCode method on each of 
> the two objects must produce distinct integer results. However, the 
> programmer should be aware that producing distinct integer results for 
> unequal objects may improve the performance of hashtables."
> So sometimes, two different objects can have the same hashCode!
> So, sometimes two calls to addElement(element) can result in only the second 
> object stored in the ConcreteElement.
> So sometimes, on out instalaltion some table rows misses, or some row cells 
> misses or...

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