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https://issues.apache.org/jira/browse/LUCENE-584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12524301
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Paul Elschot commented on LUCENE-584:
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Another way to decouple from BitSet would be to keep introduce a new superclass
of Filter that only has an abstract getMatcher() method, and to add an
implementation of that method in the current Filter class.
That would boil down to the current patch with two classes renamed:
Filter -> new class with abstract getMatcher() method.
BitSetFilter -> Filter.
This would avoid all backward compatibility issues, except for the unlikely
case in which a getMatcher() method is already implemented in an existing
subclass of Filter.
Also, to take advantage of the independence of BitSet in other implementations,
only this new class would need to be used.
The only disadvantage I can see is that Filter is not renamed to BitSetFilter,
which it actually is. But that can be fixed by making the javadoc of Filter
explicit about the use of BitSet.
For the lucene core and some of the contrib, this would mean that it would move
to this new superclass of Filter. Again, I don't expect backward compatibility
issues there.
Does anyone see any problems with this approach?
When not, what name should this new superclass of Filter have? I'm thinking of
MatchFilter, any other suggestions?
> Decouple Filter from BitSet
> ---------------------------
>
> Key: LUCENE-584
> URL: https://issues.apache.org/jira/browse/LUCENE-584
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Affects Versions: 2.0.1
> Reporter: Peter Schäfer
> Priority: Minor
> Attachments: bench-diff.txt, bench-diff.txt,
> Matcher1-ground-20070730.patch, Matcher2-default-20070730.patch,
> Matcher3-core-20070730.patch, Matcher4-contrib-misc-20070730.patch,
> Matcher5-contrib-queries-20070730.patch, Matcher6-contrib-xml-20070730.patch,
> Some Matchers.zip
>
>
> {code}
> package org.apache.lucene.search;
> public abstract class Filter implements java.io.Serializable
> {
> public abstract AbstractBitSet bits(IndexReader reader) throws IOException;
> }
> public interface AbstractBitSet
> {
> public boolean get(int index);
> }
> {code}
> It would be useful if the method =Filter.bits()= returned an abstract
> interface, instead of =java.util.BitSet=.
> Use case: there is a very large index, and, depending on the user's
> privileges, only a small portion of the index is actually visible.
> Sparsely populated =java.util.BitSet=s are not efficient and waste lots of
> memory. It would be desirable to have an alternative BitSet implementation
> with smaller memory footprint.
> Though it _is_ possibly to derive classes from =java.util.BitSet=, it was
> obviously not designed for that purpose.
> That's why I propose to use an interface instead. The default implementation
> could still delegate to =java.util.BitSet=.
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