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From "B.J. Reed (JIRA)" <j...@apache.org>
Subject [jira] Updated: (OPENJPA-1025) AbstractResultList.subList throws UnsupportedOperationException
Date Tue, 21 Apr 2009 13:41:47 GMT

     [ https://issues.apache.org/jira/browse/OPENJPA-1025?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

B.J. Reed updated OPENJPA-1025:
-------------------------------

    Attachment: OPENJPA-1025b.patch

Thanks for the quick review Julien.

Attaching OPENJPA-1025b.patch.  For the AbstractNonSequentialResultList case, I think we're
going to have to just throw a "not implemented exception".  The concrete classes for this
use Object[] underneath in stead of a List.  I don't know of a way to create a List "view"
on to an Object[] and I agree that an exception would be better than returning a modifiable
List.  Also, logically, I really wasn't sure that getting a sub list on an object that is
"non sequential" was really a good idea - doesn't seem like the data would be consistently
returned.

> AbstractResultList.subList throws UnsupportedOperationException
> ---------------------------------------------------------------
>
>                 Key: OPENJPA-1025
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-1025
>             Project: OpenJPA
>          Issue Type: Bug
>          Components: lib
>    Affects Versions: 1.2.1, 1.3.0, 2.0.0
>         Environment: http://svn.apache.org/viewvc/openjpa/trunk/openjpa-lib/src/main/java/org/apache/openjpa/lib/rop/AbstractResultList.java?revision=757278&view=markup,
> Seam 2.0, OpenJPA 1.2.1
>            Reporter: Julien Kronegg
>         Attachments: OPENJPA-1025.patch, OPENJPA-1025b.patch
>
>   Original Estimate: 4h
>  Remaining Estimate: 4h
>
> AbstractResultList implements the basics for readonly result lists. When calling the
subList(int,int) method, the following exception is raised:
>     java.lang.UnsupportedOperationException
>     at org.apache.openjpa.lib.rop.AbstractResultList.subList(AbstractResultList.java:84)
>     at org.apache.openjpa.kernel.DelegatingResultList.subList(DelegatingResultList.java:308)
>     ...
> Since the subList() method contract is to create a new List from the ResultList, this
operation does not modify the original list: it only provides a *view* on the original list
(see http://java.sun.com/docs/books/tutorial/collections/interfaces/list.html ). 
> This problem is also found by other users: http://n2.nabble.com/DelegatingResultList.subList-not-implemented--td210389.html
> They found the (bad) workaround to build a new List (bad because this is not the same
as calling subList()):
>     List mySubList = new ArrayList(openjpaList).subList(from, to);
> The AbstractResultList class should be modified by one of this solution (sorted by decreasing
preference order):
> 1) the AbstractResultList class should extends java.util.AbstractList and the subList()
method should be removed (because implemented by AbstractList)
> 2) the subList() method should be implemented to return a view on the original list.
See java.util.AbstractList for an implementation (http://www.koders.com/java/fidCFCB47A1819AB345234CC04B6A1EA7554C2C17C0.aspx?s=iso+3166
)
> 3) the subList() method should throw the exception with the message "this method is not
yet implemented. Workaround: new ArrayList(openjpaList).subList(from, to)"

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