org.apache.lucene.index

## Class BaseCompositeReader<R extends IndexReader>

- java.lang.Object
- - org.apache.lucene.index.IndexReader
  - - org.apache.lucene.index.CompositeReader
    - - org.apache.lucene.index.BaseCompositeReader<R>

- All Implemented Interfaces:
    Closeable, AutoCloseable
  Direct Known Subclasses:
    DirectoryReader, MultiReader, ParallelCompositeReader

      public abstract class BaseCompositeReader<R extends IndexReader>
      extends CompositeReader

  Base class for implementing `CompositeReader`s based on an array of sub-readers. The implementing class has to add code for correctly refcounting and closing the sub-readers.

  User code will most likely use `MultiReader` to build a composite reader on a set of sub-readers (like several `DirectoryReader`s).

  For efficiency, in this API documents are often referred to via document numbers, non-negative integers which each name a unique document in the index. These document numbers are ephemeral -- they may change as documents are added to and deleted from an index. Clients should thus not rely on a given document having the same number between sessions.

  NOTE: `IndexReader` instances are completely thread safe, meaning multiple threads can call any of its methods, concurrently. If your application requires external synchronization, you should not synchronize on the `IndexReader` instance; use your own (non-Lucene) objects instead.

  See Also:
    `MultiReader`
  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.IndexReader

      `IndexReader.ReaderClosedListener`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `BaseCompositeReader(R[] subReaders)` Constructs a `BaseCompositeReader` on the given subReaders.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `docFreq(Term term)` Returns the number of documents containing the `term`.
    `void` | `document(int docID, StoredFieldVisitor visitor)` Expert: visits the fields of a stored document, for custom processing/loading of each field.
    `protected List<? extends R>` | `getSequentialSubReaders()` Expert: returns the sequential sub readers that this reader is logically composed of.
    `Fields` | `getTermVectors(int docID)` Retrieve term vectors for this document, or null if term vectors were not indexed.
    `boolean` | `hasDeletions()` Returns true if any documents have been deleted
    `int` | `maxDoc()` Returns one greater than the largest possible document number.
    `int` | `numDocs()` Returns the number of documents in this index.
    `protected int` | `readerBase(int readerIndex)` Helper method for subclasses to get the docBase of the given sub-reader index.
    `protected int` | `readerIndex(int docID)` Helper method for subclasses to get the corresponding reader for a doc ID
    `long` | `totalTermFreq(Term term)` Returns the number of documents containing the term `term`.

    - ### Methods inherited from class org.apache.lucene.index.CompositeReader

      `getContext, toString`

    - ### Methods inherited from class org.apache.lucene.index.IndexReader

      `addReaderClosedListener, close, decRef, doClose, document, document, ensureOpen, equals, getCombinedCoreAndDeletesKey, getCoreCacheKey, getRefCount, getTermVector, hashCode, incRef, leaves, numDeletedDocs, open, open, open, open, open, registerParentReader, removeReaderClosedListener, tryIncRef`

    - ### Methods inherited from class java.lang.Object

      `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### BaseCompositeReader

          protected BaseCompositeReader(R[] subReaders)

      Constructs a `BaseCompositeReader` on the given subReaders.
      Parameters:
        `subReaders` - the wrapped sub-readers. This array is returned by `getSequentialSubReaders()` and used to resolve the correct subreader for docID-based methods. Please note: This array is not cloned and not protected for modification, the subclass is responsible to do this.

  - ### Method Detail

    - #### getTermVectors

          public final Fields getTermVectors(int docID)
                                      throws IOException

      Description copied from class: `IndexReader`
      Retrieve term vectors for this document, or null if term vectors were not indexed. The returned Fields instance acts like a single-document inverted index (the docID will be 0).
      Specified by:
        `getTermVectors` in class `IndexReader`
      Throws:
        `IOException`

    - #### numDocs

          public final int numDocs()

      Description copied from class: `IndexReader`
      Returns the number of documents in this index.
      Specified by:
        `numDocs` in class `IndexReader`

    - #### maxDoc

          public final int maxDoc()

      Description copied from class: `IndexReader`
      Returns one greater than the largest possible document number. This may be used to, e.g., determine how big to allocate an array which will have an element for every document number in an index.
      Specified by:
        `maxDoc` in class `IndexReader`

    - #### document

          public final void document(int docID,
                      StoredFieldVisitor visitor)
                              throws IOException

      Description copied from class: `IndexReader`
      Expert: visits the fields of a stored document, for custom processing/loading of each field. If you simply want to load all fields, use `IndexReader.document(int)`. If you want to load a subset, use `DocumentStoredFieldVisitor`.
      Specified by:
        `document` in class `IndexReader`
      Throws:
        `IOException`

    - #### hasDeletions

          public final boolean hasDeletions()

      Description copied from class: `IndexReader`
      Returns true if any documents have been deleted
      Specified by:
        `hasDeletions` in class `IndexReader`

    - #### docFreq

          public final int docFreq(Term term)
                            throws IOException

      Description copied from class: `IndexReader`
      Returns the number of documents containing the `term`. This method returns 0 if the term or field does not exists. This method does not take into account deleted documents that have not yet been merged away.
      Specified by:
        `docFreq` in class `IndexReader`
      Throws:
        `IOException`
      See Also:
        `TermsEnum.docFreq()`

    - #### totalTermFreq

          public final long totalTermFreq(Term term)
                                   throws IOException

      Description copied from class: `IndexReader`
      Returns the number of documents containing the term `term`. This method returns 0 if the term or field does not exists, or -1 if the Codec does not support the measure. This method does not take into account deleted documents that have not yet been merged away.
      Specified by:
        `totalTermFreq` in class `IndexReader`
      Throws:
        `IOException`
      See Also:
        `TermsEnum.totalTermFreq()`

    - #### readerIndex

          protected final int readerIndex(int docID)

      Helper method for subclasses to get the corresponding reader for a doc ID

    - #### readerBase

          protected final int readerBase(int readerIndex)

      Helper method for subclasses to get the docBase of the given sub-reader index.

    - #### getSequentialSubReaders

          protected final List<? extends R> getSequentialSubReaders()

      Description copied from class: `CompositeReader`
      Expert: returns the sequential sub readers that this reader is logically composed of. This method may not return `null`.

      NOTE: In contrast to previous Lucene versions this method is no longer public, code that wants to get all `AtomicReader`s this composite is composed of should use `IndexReader.leaves()`.

      Specified by:
        `getSequentialSubReaders` in class `CompositeReader`
      See Also:
        `IndexReader.leaves()`

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