org.apache.lucene.index

## Class IndexCommit

- java.lang.Object
- - org.apache.lucene.index.IndexCommit

- All Implemented Interfaces:
    Comparable<IndexCommit>
  Direct Known Subclasses:
    SnapshotDeletionPolicy.SnapshotCommitPoint

      public abstract class IndexCommit
      extends Object
      implements Comparable<IndexCommit>

  Expert: represents a single commit into an index as seen by the `IndexDeletionPolicy` or `IndexReader`.

  Changes to the content of an index are made visible only after the writer who made that change commits by writing a new segments file (`segments_N`). This point in time, when the action of writing of a new segments file to the directory is completed, is an index commit.

  Each index commit point has a unique segments file associated with it. The segments file associated with a later index commit point would have a larger N.

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

- - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `IndexCommit()` Sole constructor.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `compareTo(IndexCommit commit)`
    `abstract void` | `delete()` Delete this commit point.
    `boolean` | `equals(Object other)` Two IndexCommits are equal if both their Directory and versions are equal.
    `abstract Directory` | `getDirectory()` Returns the `Directory` for the index.
    `abstract Collection<String>` | `getFileNames()` Returns all index files referenced by this commit point.
    `abstract long` | `getGeneration()` Returns the generation (the _N in segments_N) for this IndexCommit
    `abstract int` | `getSegmentCount()` Returns number of segments referenced by this commit.
    `abstract String` | `getSegmentsFileName()` Get the segments file (`segments_N`) associated with this commit point.
    `abstract Map<String,String>` | `getUserData()` Returns userData, previously passed to `IndexWriter.setCommitData(Map)` for this commit.
    `int` | `hashCode()`
    `abstract boolean` | `isDeleted()` Returns true if this commit should be deleted; this is only used by `IndexWriter` after invoking the `IndexDeletionPolicy`.

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

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

- - ### Constructor Detail

    - #### IndexCommit

          protected IndexCommit()

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

  - ### Method Detail

    - #### getSegmentsFileName

          public abstract String getSegmentsFileName()

      Get the segments file (`segments_N`) associated with this commit point.

    - #### getFileNames

          public abstract Collection<String> getFileNames()
                                                   throws IOException

      Returns all index files referenced by this commit point.
      Throws:
        `IOException`

    - #### getDirectory

          public abstract Directory getDirectory()

      Returns the `Directory` for the index.

    - #### delete

          public abstract void delete()

      Delete this commit point. This only applies when using the commit point in the context of IndexWriter's IndexDeletionPolicy.

      Upon calling this, the writer is notified that this commit point should be deleted.

      Decision that a commit-point should be deleted is taken by the `IndexDeletionPolicy` in effect and therefore this should only be called by its `onInit()` or `onCommit()` methods.

    - #### isDeleted

          public abstract boolean isDeleted()

      Returns true if this commit should be deleted; this is only used by `IndexWriter` after invoking the `IndexDeletionPolicy`.

    - #### getSegmentCount

          public abstract int getSegmentCount()

      Returns number of segments referenced by this commit.

    - #### equals

          public boolean equals(Object other)

      Two IndexCommits are equal if both their Directory and versions are equal.
      Overrides:
        `equals` in class `Object`

    - #### hashCode

          public int hashCode()

      Overrides:
        `hashCode` in class `Object`

    - #### getGeneration

          public abstract long getGeneration()

      Returns the generation (the _N in segments_N) for this IndexCommit

    - #### getUserData

          public abstract Map<String,String> getUserData()
                                                  throws IOException

      Returns userData, previously passed to `IndexWriter.setCommitData(Map)` for this commit. Map is String -> String.
      Throws:
        `IOException`

    - #### compareTo

          public int compareTo(IndexCommit commit)

      Specified by:
        `compareTo` in interface `Comparable<IndexCommit>`

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