org.apache.lucene.store

## Class IndexInput

- java.lang.Object
- - org.apache.lucene.store.DataInput
  - - org.apache.lucene.store.IndexInput

- All Implemented Interfaces:
    Closeable, AutoCloseable, Cloneable
  Direct Known Subclasses:
    BufferedIndexInput, ByteArrayIndexInput, ByteBuffersIndexInput, ChecksumIndexInput, RAMInputStream

      public abstract class IndexInput
      extends DataInput
      implements Cloneable, Closeable

  Abstract base class for input from a file in a `Directory`. A random-access input stream. Used for all Lucene index input operations.

  `IndexInput` may only be used from one thread, because it is not thread safe (it keeps internal state like file position). To allow multithreaded use, every `IndexInput` instance must be cloned before it is used in another thread. Subclasses must therefore implement `clone()`, returning a new `IndexInput` which operates on the same underlying resource, but positioned independently.

  Warning: Lucene never closes cloned `IndexInput`s, it will only call `close()` on the original object.

  If you access the cloned IndexInput after closing the original object, any `readXXX` methods will throw `AlreadyClosedException`.

  See Also:
    `Directory`

- - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `IndexInput(String resourceDescription)` resourceDescription should be a non-null, opaque string describing this resource; it's returned from `toString()`.

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `IndexInput` | `clone()` Returns a clone of this stream.
    `abstract void` | `close()` Closes the stream to further operations.
    `abstract long` | `getFilePointer()` Returns the current position in this file, where the next read will occur.
    `protected String` | `getFullSliceDescription(String sliceDescription)` Subclasses call this to get the String for resourceDescription of a slice of this `IndexInput`.
    `abstract long` | `length()` The number of bytes in the file.
    `RandomAccessInput` | `randomAccessSlice(long offset, long length)` Creates a random-access slice of this index input, with the given offset and length.
    `abstract void` | `seek(long pos)` Sets current position in this file, where the next read will occur.
    `abstract IndexInput` | `slice(String sliceDescription, long offset, long length)` Creates a slice of this index input, with the given description, offset, and length.
    `String` | `toString()`

    - ### Methods inherited from class org.apache.lucene.store.DataInput

      `readByte, readBytes, readBytes, readInt, readLong, readMapOfStrings, readSetOfStrings, readShort, readString, readVInt, readVLong, readZInt, readZLong, skipBytes`

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

      `equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### IndexInput

          protected IndexInput(String resourceDescription)

      resourceDescription should be a non-null, opaque string describing this resource; it's returned from `toString()`.

  - ### Method Detail

    - #### close

          public abstract void close()
                              throws IOException

      Closes the stream to further operations.
      Specified by:
        `close` in interface `Closeable`
      Specified by:
        `close` in interface `AutoCloseable`
      Throws:
        `IOException`

    - #### getFilePointer

          public abstract long getFilePointer()

      Returns the current position in this file, where the next read will occur.
      See Also:
        `seek(long)`

    - #### seek

          public abstract void seek(long pos)
                             throws IOException

      Sets current position in this file, where the next read will occur. If this is beyond the end of the file then this will throw `EOFException` and then the stream is in an undetermined state.
      Throws:
        `IOException`
      See Also:
        `getFilePointer()`

    - #### length

          public abstract long length()

      The number of bytes in the file.

    - #### toString

          public String toString()

      Overrides:
        `toString` in class `Object`

    - #### clone

          public IndexInput clone()

      Returns a clone of this stream.

      Clones of a stream access the same data, and are positioned at the same point as the stream they were cloned from.

      Expert: Subclasses must ensure that clones may be positioned at different points in the input from each other and from the stream they were cloned from.

      Warning: Lucene never closes cloned `IndexInput`s, it will only call `close()` on the original object.

      If you access the cloned IndexInput after closing the original object, any `readXXX` methods will throw `AlreadyClosedException`.

      This method is NOT thread safe, so if the current `IndexInput` is being used by one thread while `clone` is called by another, disaster could strike.

      Overrides:
        `clone` in class `DataInput`

    - #### slice

          public abstract IndexInput slice(String sliceDescription,
                                           long offset,
                                           long length)
                                    throws IOException

      Creates a slice of this index input, with the given description, offset, and length. The slice is seeked to the beginning.
      Throws:
        `IOException`

    - #### getFullSliceDescription

          protected String getFullSliceDescription(String sliceDescription)

      Subclasses call this to get the String for resourceDescription of a slice of this `IndexInput`.

    - #### randomAccessSlice

          public RandomAccessInput randomAccessSlice(long offset,
                                                     long length)
                                              throws IOException

      Creates a random-access slice of this index input, with the given offset and length.

      The default implementation calls `slice(java.lang.String, long, long)`, and it doesn't support random access, it implements absolute reads as seek+read.

      Throws:
        `IOException`

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