Package org.apache.lucene.index

Class TermsEnum

java.lang.Object

org.apache.lucene.index.TermsEnum

All Implemented Interfaces:

BytesRefIterator

Direct Known Subclasses:

BaseTermsEnum, FilteredTermsEnum, FilterLeafReader.FilterTermsEnum

public abstract class TermsEnum
extends Object
implements BytesRefIterator

Iterator to seek (seekCeil(BytesRef), seekExact(BytesRef)) or step through (BytesRefIterator.next() terms to obtain frequency information (docFreq()), PostingsEnum or PostingsEnum for the current term (postings(org.apache.lucene.index.PostingsEnum).

Term enumerations are always ordered by BytesRef.compareTo, which is Unicode sort order if the terms are UTF-8 bytes. Each term in the enumeration is greater than the one before it.

The TermsEnum is unpositioned when you first obtain it and you must first successfully call BytesRefIterator.next() or one of the seek methods.

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

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static enum	TermsEnum.SeekStatus	Represents returned result from seekCeil(org.apache.lucene.util.BytesRef).

Field Summary

Fields

Modifier and Type	Field	Description
static final TermsEnum	EMPTY	An empty TermsEnum for quickly returning an empty instance e.g.

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	TermsEnum()	Sole constructor.

Method Summary

Modifier and Type	Method	Description
abstract AttributeSource	attributes()	Returns the related attributes.
abstract int	docFreq()	Returns the number of documents containing the current term.
abstract ImpactsEnum	impacts(int flags)	Return a ImpactsEnum.
abstract long	ord()	Returns ordinal position for current term.
final PostingsEnum	postings(PostingsEnum reuse)	Get PostingsEnum for the current term.
abstract PostingsEnum	postings(PostingsEnum reuse, int flags)	Get PostingsEnum for the current term, with control over whether freqs, positions, offsets or payloads are required.
abstract IOBooleanSupplier	prepareSeekExact(BytesRef text)	Two-phase seekExact(org.apache.lucene.util.BytesRef).
abstract TermsEnum.SeekStatus	seekCeil(BytesRef text)	Seeks to the specified term, if it exists, or to the next (ceiling) term.
abstract void	seekExact(long ord)	Seeks to the specified term by ordinal (position) as previously returned by ord().
abstract boolean	seekExact(BytesRef text)	Attempts to seek to the exact term, returning true if the term is found.
abstract void	seekExact(BytesRef term, TermState state)	Expert: Seeks a specific position by TermState previously obtained from termState().
abstract BytesRef	term()	Returns current term.
abstract TermState	termState()	Expert: Returns the TermsEnums internal state to position the TermsEnum without re-seeking the term dictionary.
abstract long	totalTermFreq()	Returns the total number of occurrences of this term across all documents (the sum of the freq() for each doc that has this term).

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.lucene.util.BytesRefIterator

next

Field Details

EMPTY

public static final TermsEnum EMPTY

An empty TermsEnum for quickly returning an empty instance e.g. in MultiTermQuery

Please note: This enum should be unmodifiable, but it is currently possible to add Attributes to it. This should not be a problem, as the enum is always empty and the existence of unused Attributes does not matter.

Constructor Details

TermsEnum

protected TermsEnum()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Details

attributes

public abstract AttributeSource attributes()

Returns the related attributes.

seekExact

public abstract boolean seekExact(BytesRef text)
                           throws IOException

Attempts to seek to the exact term, returning true if the term is found. If this returns false, the enum is unpositioned. For some codecs, seekExact may be substantially faster than seekCeil(org.apache.lucene.util.BytesRef).

Returns:

true if the term is found; return false if the enum is unpositioned.

Throws:

IOException

prepareSeekExact

public abstract IOBooleanSupplier prepareSeekExact(BytesRef text)
                                            throws IOException

Two-phase seekExact(org.apache.lucene.util.BytesRef). The first phase typically calls IndexInput.prefetch(long, long) on the right range of bytes under the hood, while the second phase IOBooleanSupplier.get() actually seeks the term within these bytes. This can be used to parallelize I/O across multiple terms by calling prepareSeekExact(org.apache.lucene.util.BytesRef) on multiple terms enums before calling IOBooleanSupplier.get().

NOTE: It is illegal to call other methods on this TermsEnum after calling this method until IOBooleanSupplier.get() is called.

NOTE: This may return null if this TermsEnum can identify that the term may not exist without performing any I/O.

NOTE: The returned IOBooleanSupplier must be consumed in the same thread.

Throws:

IOException

seekCeil

public abstract TermsEnum.SeekStatus seekCeil(BytesRef text)
                                       throws IOException

Seeks to the specified term, if it exists, or to the next (ceiling) term. Returns SeekStatus to indicate whether exact term was found, a different term was found, or EOF was hit. The target term may be before or after the current term. If this returns SeekStatus.END, the enum is unpositioned.

Throws:

IOException

seekExact

public abstract void seekExact(long ord)
                        throws IOException

Seeks to the specified term by ordinal (position) as previously returned by ord(). The target ord may be before or after the current ord, and must be within bounds.

Throws:

IOException

seekExact

public abstract void seekExact(BytesRef term,
 TermState state)
                        throws IOException

Expert: Seeks a specific position by TermState previously obtained from termState(). Callers should maintain the TermState to use this method. Low-level implementations may position the TermsEnum without re-seeking the term dictionary.

Seeking by TermState should only be used iff the state was obtained from the same TermsEnum instance.

NOTE: Using this method with an incompatible TermState might leave this TermsEnum in undefined state. On a segment level TermState instances are compatible only iff the source and the target TermsEnum operate on the same field. If operating on segment level, TermState instances must not be used across segments.

NOTE: A seek by TermState might not restore the AttributeSource's state. AttributeSource states must be maintained separately if this method is used.

Parameters:

term - the term the TermState corresponds to

state - the TermState

Throws:

IOException

term

public abstract BytesRef term()
                       throws IOException

Returns current term. Do not call this when the enum is unpositioned.

Throws:

IOException

ord

public abstract long ord()
                  throws IOException

Returns ordinal position for current term. This is an optional method (the codec may throw UnsupportedOperationException). Do not call this when the enum is unpositioned.

Throws:

IOException

docFreq

public abstract int docFreq()
                     throws IOException

Returns the number of documents containing the current term. Do not call this when the enum is unpositioned. TermsEnum.SeekStatus.END.

Throws:

IOException

totalTermFreq

public abstract long totalTermFreq()
                            throws IOException

Returns the total number of occurrences of this term across all documents (the sum of the freq() for each doc that has this term). Note that, like other term measures, this measure does not take deleted documents into account.

Throws:

IOException

postings

public final PostingsEnum postings(PostingsEnum reuse)
                            throws IOException

Get PostingsEnum for the current term. Do not call this when the enum is unpositioned. This method will not return null.

NOTE: the returned iterator may return deleted documents, so deleted documents have to be checked on top of the PostingsEnum.

Use this method if you only require documents and frequencies, and do not need any proximity data. This method is equivalent to postings(reuse, PostingsEnum.FREQS)

Parameters:

reuse - pass a prior PostingsEnum for possible reuse

Throws:

IOException

See Also:

• postings(PostingsEnum, int)

postings

public abstract PostingsEnum postings(PostingsEnum reuse,
 int flags)
                               throws IOException

Get PostingsEnum for the current term, with control over whether freqs, positions, offsets or payloads are required. Do not call this when the enum is unpositioned. This method will not return null.

NOTE: the returned iterator may return deleted documents, so deleted documents have to be checked on top of the PostingsEnum.

Parameters:

reuse - pass a prior PostingsEnum for possible reuse

flags - specifies which optional per-document values you require; see PostingsEnum.FREQS

Throws:

IOException

impacts

public abstract ImpactsEnum impacts(int flags)
                             throws IOException

Return a ImpactsEnum.

Throws:

IOException

See Also:

• postings(PostingsEnum, int)

termState

public abstract TermState termState()
                             throws IOException

Expert: Returns the TermsEnums internal state to position the TermsEnum without re-seeking the term dictionary.

NOTE: A seek by TermState might not capture the AttributeSource's state. Callers must maintain the AttributeSource states separately

Throws:

IOException

See Also:

• TermState
• seekExact(BytesRef, TermState)