[jira] Commented: (COLLECTIONS-246) LoopingListIterator behaves unexpected on next and previous mixed

["Henri Yandell (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/COLLECTIONS-246?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12584429#action_12584429 ] 

Henri Yandell commented on COLLECTIONS-246:
-------------------------------------------


The basic case that I think that has to be expected is:

{code:java}
Object o1 = it.next();
Object o2 = it.previous();

assertTrue(o1 == o2) 
{code}

".next()" moves the current position. So it's right for the it.previous() to return "0" and not "2". 

Previously I suggested that a different approach of getNext and moveToNext might be useful, but that would a) confuse by adding a duplicate layer and b) would not match the Collections API java.util.Iterator pattern. So I don't think there's anything to do here - the iterators work to the same pattern as the JDK's Iterator.

> LoopingListIterator behaves unexpected on next and previous mixed
> -----------------------------------------------------------------
>
>                 Key: COLLECTIONS-246
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-246
>             Project: Commons Collections
>          Issue Type: Bug
>          Components: Iterator
>    Affects Versions: 3.2
>         Environment: JDK 1.4.2_12 
> Common Collections 3.2
>            Reporter: Frank Hefter
>            Priority: Blocker
>             Fix For: 3.3
>
>         Attachments: LoopingListIterator.java, LoopingListIterator.java, LoopingListIteratorTest.java
>
>
> Using ArrayList as the backing list. 
> This combination at least returns unexpected results as you can see in the testcase below.
> I used this for a list navigator in a web frontend and had trouble with users.
> I suspect java.util.AbstrList$ListItr (role of "cursor" var seems to be wrong implemented ) to cause this problem. If so maybe we have to implement it in a different way.
> Testcase (it runs without hassle but the comments show whats wrong):
> -------------------------------------------
> import java.util.ArrayList;
> import junit.framework.TestCase;
> import org.apache.commons.collections.iterators.LoopingListIterator;
> public class SelectionControllerTest extends TestCase {
>     public void testSelectorForApache() {
>         ArrayList al = new ArrayList();
>         al.add("0"); al.add("1"); al.add("2");
>         LoopingListIterator it = new  LoopingListIterator(al);
>         assertEquals("0", it.next()); // This is OK
>         // here I am on "0"
>         assertEquals("0", it.previous()); // Wrong ! This should be 2!
>         //      here I am on "0" too! This is wrong.
>         assertEquals("2", it.previous());
>         assertEquals("1", it.previous());
>         assertEquals("0", it.previous());
>         assertEquals("2", it.previous());
>         // here I am on "2" 
>         assertEquals("2", it.next()); // Wrong ! This should be 0!
>         // here I am on "2" too! This is wrong.
>         assertEquals("0", it.next()); 
>         assertEquals("1", it.next());
>         // here I am on "1"         
>         assertEquals("1", it.previous()); // Wrong ! This should be 0!
>     }
> }
> -------------------------------------------
> Thanks for your help.

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