org.apache.lucene.search
Class FilteredDocIdSet

java.lang.Object
  extended by org.apache.lucene.search.DocIdSet
      extended by org.apache.lucene.search.FilteredDocIdSet
Direct Known Subclasses:
BitsFilteredDocIdSet

public abstract class FilteredDocIdSet
extends DocIdSet

Abstract decorator class for a DocIdSet implementation that provides on-demand filtering/validation mechanism on a given DocIdSet.

Technically, this same functionality could be achieved with ChainedFilter (under queries/), however the benefit of this class is it never materializes the full bitset for the filter. Instead, the match(int) method is invoked on-demand, per docID visited during searching. If you know few docIDs will be visited, and the logic behind match(int) is relatively costly, this may be a better way to filter than ChainedFilter.

See Also:
DocIdSet

Constructor Summary
FilteredDocIdSet(DocIdSet innerSet)
          Constructor.
 
Method Summary
 Bits bits()
          Optionally provides a Bits interface for random access to matching documents.
 boolean isCacheable()
          This DocIdSet implementation is cacheable if the inner set is cacheable.
 DocIdSetIterator iterator()
          Implementation of the contract to build a DocIdSetIterator.
protected abstract  boolean match(int docid)
          Validation method to determine whether a docid should be in the result set.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

FilteredDocIdSet

public FilteredDocIdSet(DocIdSet innerSet)
Constructor.

Parameters:
innerSet - Underlying DocIdSet
Method Detail

isCacheable

public boolean isCacheable()
This DocIdSet implementation is cacheable if the inner set is cacheable.

Overrides:
isCacheable in class DocIdSet

bits

public Bits bits()
          throws IOException
Description copied from class: DocIdSet
Optionally provides a Bits interface for random access to matching documents.

Overrides:
bits in class DocIdSet
Returns:
null, if this DocIdSet does not support random access. In contrast to DocIdSet.iterator(), a return value of null does not imply that no documents match the filter! The default implementation does not provide random access, so you only need to implement this method if your DocIdSet can guarantee random access to every docid in O(1) time without external disk access (as Bits interface cannot throw IOException). This is generally true for bit sets like FixedBitSet, which return itself if they are used as DocIdSet.
Throws:
IOException

match

protected abstract boolean match(int docid)
Validation method to determine whether a docid should be in the result set.

Parameters:
docid - docid to be tested
Returns:
true if input docid should be in the result set, false otherwise.

iterator

public DocIdSetIterator iterator()
                          throws IOException
Implementation of the contract to build a DocIdSetIterator.

Specified by:
iterator in class DocIdSet
Throws:
IOException
See Also:
DocIdSetIterator, FilteredDocIdSetIterator


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