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https://issues.apache.org/jira/browse/COLLECTIONS-310?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13592633#comment-13592633
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Thomas Vahrst commented on COLLECTIONS-310:
-------------------------------------------
SetUniqueListTest.java now contains some new testcases to test the behavior of
listiterators of sublists.
SetUniqueList.v2.java is the 2nd variant I implemented. In contrast to the
first attempt, this class does not inherit from AbstractListDecorator but
inherits from java.util.AbstractList. It holds a reference to a underlying list
which is *shared* with all sublists. So every sublist holds the reference to
the underlying list and maintains it's own set and a offset of its element
range in the underlying list.
This variant contains support for iterators and listiterators on sublists.
I personally found this solution a bit more elegant than the first variant.
> 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, SetUniqueListTest.java, SetUniqueList.v2.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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