org.apache.lucene.index

Class AutomatonTermsEnum

java.lang.Object

org.apache.lucene.index.TermsEnum

org.apache.lucene.index.FilteredTermsEnum

org.apache.lucene.index.AutomatonTermsEnum

All Implemented Interfaces:

BytesRefIterator

public class AutomatonTermsEnum
extends FilteredTermsEnum

A FilteredTermsEnum that enumerates terms based upon what is accepted by a DFA.

The algorithm is such:

1. As long as matches are successful, keep reading sequentially.
2. When a match fails, skip to the next string in lexicographic order that does not enter a reject state.

The algorithm does not attempt to actually skip to the next string that is completely accepted. This is not possible when the language accepted by the FSM is not finite (i.e. * operator).

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.index.FilteredTermsEnum

FilteredTermsEnum.AcceptStatus

Nested classes/interfaces inherited from class org.apache.lucene.index.TermsEnum

TermsEnum.SeekStatus

Field Summary

Fields inherited from class org.apache.lucene.index.FilteredTermsEnum

actualTerm, tenum

Fields inherited from class org.apache.lucene.index.TermsEnum

EMPTY

Constructor Summary

Constructors

Constructor and Description
AutomatonTermsEnum(TermsEnum tenum, CompiledAutomaton compiled) Construct an enumerator based upon an automaton, enumerating the specified field, working on a supplied TermsEnum

Method Summary

Modifier and Type	Method and Description
protected FilteredTermsEnum.AcceptStatus	accept(BytesRef term) Returns true if the term matches the automaton.
protected BytesRef	nextSeekTerm(BytesRef term) On the first call to FilteredTermsEnum.next() or if FilteredTermsEnum.accept(org.apache.lucene.util.BytesRef) returns FilteredTermsEnum.AcceptStatus.YES_AND_SEEK or FilteredTermsEnum.AcceptStatus.NO_AND_SEEK, this method will be called to eventually seek the underlying TermsEnum to a new position.

Methods inherited from class org.apache.lucene.index.FilteredTermsEnum

attributes, docFreq, next, ord, postings, seekCeil, seekExact, seekExact, seekExact, setInitialSeekTerm, term, termState, totalTermFreq

Methods inherited from class org.apache.lucene.index.TermsEnum

postings

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AutomatonTermsEnum

public AutomatonTermsEnum(TermsEnum tenum,
                          CompiledAutomaton compiled)

Construct an enumerator based upon an automaton, enumerating the specified field, working on a supplied TermsEnum

Parameters:

compiled - CompiledAutomaton

WARNING: This API is experimental and might change in incompatible ways in the next release.

Method Detail

accept

protected FilteredTermsEnum.AcceptStatus accept(BytesRef term)

Returns true if the term matches the automaton. Also stashes away the term to assist with smart enumeration.

Specified by:

accept in class FilteredTermsEnum

nextSeekTerm

protected BytesRef nextSeekTerm(BytesRef term)
                         throws IOException

Description copied from class: FilteredTermsEnum

On the first call to FilteredTermsEnum.next() or if FilteredTermsEnum.accept(org.apache.lucene.util.BytesRef) returns FilteredTermsEnum.AcceptStatus.YES_AND_SEEK or FilteredTermsEnum.AcceptStatus.NO_AND_SEEK, this method will be called to eventually seek the underlying TermsEnum to a new position. On the first call, currentTerm will be null, later calls will provide the term the underlying enum is positioned at. This method returns per default only one time the initial seek term and then null, so no repositioning is ever done.

Override this method, if you want a more sophisticated TermsEnum, that repositions the iterator during enumeration. If this method always returns null the enum is empty.

Please note: This method should always provide a greater term than the last enumerated term, else the behaviour of this enum violates the contract for TermsEnums.

Overrides:

nextSeekTerm in class FilteredTermsEnum

Throws:

IOException