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https://issues.apache.org/jira/browse/COLLECTIONS-310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13573550#comment-13573550
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Thomas Neidhart commented on COLLECTIONS-310:
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Right now, when calling subList, a new, independent SetUniqueList is created
which is filled with elements from the backing list of the specified range.
The problem comes from the fact that this new SetUniqueList does not check for
uniqueness in the backing list, but only in the sublist. If we would create an
inner class (see for example ListOrderedMap), which would delegate the calls
(after properly adjusting some arguments, e.g. calculate real index) to the
backing SeUniqueList we could support the sublist contract.
The order is maintained and the uniqueness is validated by the backing list.
What do you think?
> 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
>
>
> 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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