Filter/query using a List ?

Question

Hi,
I'm trying to create a query using a filter where the criteria is equality on a list (ie. an ordered collection).
I.e
Using the ReflectionExtractor where the method returns an ArrayList and using the EqualsFilter, eg EqualsFilter(ArrayList.., ArrayList..)
This produces an exception (ClassCastException) where using a set instead of a list works..
Is there a recommended solution to do this as I can't see an existing filter that supports this, have I missed something, do I create a custom filter, do I use a comparator for the extractor (is this efficient)..
Thanks
Jesper

Answer 1

Hi Jesper,
you need not extend the EqualsFilter to use indexes.
You just need to ensure that the equals() method of the return value (the specialized collection) does what you want, and also that you have the appropriately typed collection on both sides of the comparison. Naturally you also need to implement hashCode() by the collection class appropriately, so that it always returns the same hash code for instances for which equals() return true.
One side is provided by the extractor/method return value, the other is provided by the parameter to the filter constructor.
All the EqualsFilter does when using an index is looking up a collection of cache keys from a hash-based map keyed by the extracted value (i.e. the return value of your method). These are the keys to the cached values from which the extracted value is extracted from.
It's not Coherence which has to support out of the box ordered collections. Coherence supports using the equals() method.
If equals() is not implemented how you would like to do equality checking, then obviously you will not get the expected result. By default a list equals method uses the default Object.equals() check which is reference equality. This will always yield false in a pass-by-value environment.
You have to implement equals() and hashCode() properly for all object types which you want to use as an indexed method return value.
Best regards,
Robert