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https://issues.apache.org/jira/browse/COLLECTIONS-530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14013593#comment-14013593
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Thomas Neidhart commented on COLLECTIONS-530:
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The reason why the PredicatedXXX decorators throw an exception rather than
silently discard the element is related to the Collection contract which states
the following (add method):
{noformat}
If a collection refuses to add a particular element for any reason other than
that it already contains the element, it must throw an exception (rather than
returning false). This preserves the invariant that a collection always
contains the specified element after this call returns.
{noformat}
We did violate the Collection contract at other occasions in the past (see Bag
interface), but it was not a very wise choice imho (and we still suffer from
it). So atm I do not see a convincing argument to add something like this to a
general-purpose lib as collections. If you just want to filter certain elements
from a given collection, you might better use CollectionUtils.filter(...).
> Rejecting items on predicate failure without throwing an Exception
> ------------------------------------------------------------------
>
> Key: COLLECTIONS-530
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-530
> Project: Commons Collections
> Issue Type: Improvement
> Components: List
> Affects Versions: 4.0
> Reporter: Erik
>
> The PredicatedList class doesn't allow entries that fail the predicate, but
> throws an Exception on entry.
> The problem I have with this, is that it places the onus of filtering out
> invalid entries on the caller.
> I typically add items in a loop. The item added is the result of a method
> call (which returns null if it can't create one).
> This problem is so common for me that I have created my own FilteredList
> class that simply ignores invalid entries.
> I would like the PredicatedList class to be capable of rejecting items
> without throwing an exception.
> I don't mind writing the code for this, but there are a great many ways in
> which this can be done.
> So I was wondering what the interface should look like.
> Separate FilteredList class.
> Works, but seems a little verbose for the purpose
> New factory method: filteredList(List<T> list, Predicate<? super T>
> predicate)
> Nice and simple, but doesn't allow extension; other ways of dealing with
> predicate failure.
> New factory method with enum: predicatedList(List<T> list, Predicate<? super
> T> predicate, PredicateFailEnum action)
> More verbose to use and adds an extra class, but allows more alternative ways
> to deal with predicate failure.
> One more nice thing is that it might be less confusing,
> because choosing between predicatedList and the above filteredList might not
> be so obvious.
> New factory method with interface: filteredList(List<T> list, Predicate<?
> super T> predicate, PredicateFailInterface action)
> Complex, but the most flexible way of dealing with predicate failure.
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