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, FuzzyTermsEnum
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.

  • 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

    • 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

      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:

    • 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: