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From "Thomas Vahrst (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (COLLECTIONS-310) Modifications of a SetUniqueList.subList() invalidate the parent list
Date Mon, 18 Feb 2013 20:55:12 GMT

    [ https://issues.apache.org/jira/browse/COLLECTIONS-310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13580821#comment-13580821
] 

Thomas Vahrst edited comment on COLLECTIONS-310 at 2/18/13 8:54 PM:
--------------------------------------------------------------------

SetUniqueList.patch contains JUnit Tests and Variant No. 1 for SetUniqueList. I am not sure
whether the patch has a correct format (I am not able to re-apply the patch in Netbeans...)
so I attached the corresponding java files as well.

Some comment to this solution: 
1. During the implementation I recognized, that the existing implementation of subList() uses
the subList() method on the decorated list and then creates a new Set and fills all elements
of the sublist into the set. 

Now this issue requires, that a parent list has to be modified on certain invocations on a
sublist - for example when adding an element to the sublist which exists in the parent list
somewhere outside the range of the sublist. With the current sublist implementation, any attempt
to modify a parent list fails with a ConcurrentModifiationException. So we have to reimplement
the sublist functionality inside SetUniqueList and can not reuse the service of AbstractListDecorator.

2. When we create a subList on a SetUniqueList, this sublist has to obbey the SetUniqueList
contracts. The original parent list will have slightly different behavior when adding or setting
values. When we create a second sublist based on the first sublist, this top most list has
to provide SetUniqueList semantics.

Example (from JUnit Tests)
{noformat} 
 subList2                    ! e ! f ! g !              offset = 2
 subList1            ! c ! d ! e ! f ! g ! h !          offset = 2
 list        ! a ! b ! c ! d ! e ! f ! g ! h ! i ! j !  offset = 0
             -----------------------------------------
 Index         0   1   2   3   4   5   6   7   8   9

 Tests adding a 'd' to subList2. This should move the 'd' in subList1 and list in the range
of subList2
 Expected result:

 subList2                ! e ! f ! g ! d !              offset = 1
 subList1            ! c ! e ! f ! g ! d ! h !          offset = 2
 list        ! a ! b ! c ! e ! f ! g ! d ! h ! i ! j !  offset = 0
             -----------------------------------------
 Index         0   1   2   3   4   5   6   7   8   9
{noformat} 











                
      was (Author: t.vahrst):
    SetUniqueList.patch contains JUnit Tests and Variant No. 1 for SetUniqueList. I am not
sure whether the patch has a correct format (I am not able to re-apply the patch in Netbeans...)
so I attached the corresponding java files as well.


                  
> Modifications of a SetUniqueList.subList() invalidate the parent list
> ---------------------------------------------------------------------
>
>                 Key: COLLECTIONS-310
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-310
>             Project: Commons Collections
>          Issue Type: Bug
>          Components: List
>    Affects Versions: 3.2, Nightly Builds
>            Reporter: Christian Semrau
>            Priority: Minor
>             Fix For: 4.0
>
>         Attachments: SetUniqueList.java, SetUniqueList.patch, SetUniqueListTest.java
>
>
> The List returned by SetUniqueList.subList() is again a SetUniqueList. The contract for
List.subList() says that the returned list supports all the operations of the parent list,
and it is backed by the parent list.
> We have a SetUniqueList uniqueList equal to {"Hello", "World"}. We get a subList containing
the last element. Now we add the element "Hello", contained in the uniqueList but not in the
subList, to the subList.
> What should happen?
> Should the subList behave like a SetUniqueList and add the element - meaning that it
changes position in the uniqueList because at the old place it gets removed, so now uniqueList
equals {"World", "Hello"} (which fails)?
> Or should the element not be added, because it is already contained in the parent list,
thereby violating the SetUniqueList-ness of the subList (which fails)?
> I prefer the former behaviour, because modifications should only be made through the
subList and not through the parent list (as explained in List.subList()).
> What should happen if we replace (using set) the subList element "World" with "Hello"
instead of adding an element?
> The subList should contain only "Hello", and for the parent list, the old element 0 (now
a duplicate of the just set element 1) should be removed (which fails).
> And of course the parent list should know what happens to it (specifically, its uniqueness
Set) (which fails in the current snapshot).
> 	public void testSubListAddNew() {
> 		List uniqueList = SetUniqueList.decorate(new ArrayList());
> 		uniqueList.add("Hello");
> 		uniqueList.add("World");
> 		List subList = uniqueList.subList(1, 2);
> 		subList.add("Goodbye");
> 		List expectedSubList = Arrays.asList(new Object[] { "World", "Goodbye" });
> 		List expectedParentList = Arrays.asList(new Object[] { "Hello", "World", "Goodbye"
});
> 		assertEquals(expectedSubList, subList);
> 		assertEquals(expectedParentList, uniqueList);
> 		assertTrue(uniqueList.contains("Goodbye")); // fails
> 	}
> 	public void testSubListAddDuplicate() {
> 		List uniqueList = SetUniqueList.decorate(new ArrayList());
> 		uniqueList.add("Hello");
> 		uniqueList.add("World");
> 		List subList = uniqueList.subList(1, 2);
> 		subList.add("Hello");
> 		List expectedSubList = Arrays.asList(new Object[] { "World", "Hello" });
> 		List expectedParentList = Arrays.asList(new Object[] { "World", "Hello" });
> 		assertEquals(expectedSubList, subList);
> 		assertEquals(expectedParentList, uniqueList); // fails
> 	}
> 	public void testSubListSetDuplicate() {
> 		List uniqueList = SetUniqueList.decorate(new ArrayList());
> 		uniqueList.add("Hello");
> 		uniqueList.add("World");
> 		List subList = uniqueList.subList(1, 2);
> 		subList.set(0, "Hello");
> 		List expectedSubList = Arrays.asList(new Object[] { "Hello" });
> 		List expectedParentList = Arrays.asList(new Object[] { "Hello" });
> 		assertEquals(expectedSubList, subList);
> 		assertEquals(expectedParentList, uniqueList); // fails
> 	}

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