Package org.apache.lucene.store

# Class DataOutput

java.lang.Object
org.apache.lucene.store.DataOutput

Direct Known Subclasses:
  `ByteArrayDataOutput`, `ByteBuffersDataOutput`, `IndexOutput`, `OutputStreamDataOutput`, `PagedBytes.PagedBytesDataOutput`

public abstract class DataOutput extends Object
Abstract base class for performing write operations of Lucene's low-level data types.

`DataOutput` may only be used from one thread, because it is not thread safe (it keeps internal state like file position).

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `DataOutput()`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `copyBytes(DataInput input, long numBytes)`
  Copy numBytes bytes from input to ourself.
  `abstract void`
  `writeByte(byte b)`
  Writes a single byte.
  `void`
  `writeBytes(byte[] b, int length)`
  Writes an array of bytes.
  `abstract void`
  `writeBytes(byte[] b, int offset, int length)`
  Writes an array of bytes.
  `void`
  `writeGroupVInts(int[] values, int limit)`
  Encode integers using group-varint.
  `void`
  `writeGroupVInts(long[] values, int limit)`
  Deprecated.
  This method is preserved only for backwards codecs
  `void`
  `writeInt(int i)`
  Writes an int as four bytes (LE byte order).
  `void`
  `writeLong(long i)`
  Writes a long as eight bytes (LE byte order).
  `void`
  `writeMapOfStrings(Map<String,String> map)`
  Writes a String map.
  `void`
  `writeSetOfStrings(Set<String> set)`
  Writes a String set.
  `void`
  `writeShort(short i)`
  Writes a short as two bytes (LE byte order).
  `void`
  `writeString(String s)`
  Writes a string.
  `final void`
  `writeVInt(int i)`
  Writes an int in a variable-length format.
  `final void`
  `writeVLong(long i)`
  Writes an long in a variable-length format.
  `final void`
  `writeZInt(int i)`
  Write a `zig-zag`-encoded `variable-length` integer.
  `final void`
  `writeZLong(long i)`
  Write a `zig-zag`-encoded `variable-length` long.

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

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

- ## Constructor Details

  - ### DataOutput

    public DataOutput()

- ## Method Details

  - ### writeByte

    public abstract void writeByte(byte b) throws IOException
    Writes a single byte.

    The most primitive data type is an eight-bit byte. Files are accessed as sequences of bytes. All other data types are defined as sequences of bytes, so file formats are byte-order independent.

    Throws:
      `IOException`
    See Also:
      - `DataInput.readByte()`

  - ### writeBytes

    public void writeBytes(byte[] b, int length) throws IOException
    Writes an array of bytes.
    Parameters:
      `b` - the bytes to write
      `length` - the number of bytes to write
    Throws:
      `IOException`
    See Also:
      - `DataInput.readBytes(byte[],int,int)`

  - ### writeBytes

    public abstract void writeBytes(byte[] b, int offset, int length) throws IOException
    Writes an array of bytes.
    Parameters:
      `b` - the bytes to write
      `offset` - the offset in the byte array
      `length` - the number of bytes to write
    Throws:
      `IOException`
    See Also:
      - `DataInput.readBytes(byte[],int,int)`

  - ### writeInt

    public void writeInt(int i) throws IOException
    Writes an int as four bytes (LE byte order).
    Throws:
      `IOException`
    See Also:
      - `DataInput.readInt()`
      - `BitUtil.VH_LE_INT`

  - ### writeShort

    public void writeShort(short i) throws IOException
    Writes a short as two bytes (LE byte order).
    Throws:
      `IOException`
    See Also:
      - `DataInput.readShort()`
      - `BitUtil.VH_LE_SHORT`

  - ### writeVInt

    public final void writeVInt(int i) throws IOException
    Writes an int in a variable-length format. Writes between one and five bytes. Smaller values take fewer bytes. Negative numbers are supported, but should be avoided.

    VByte is a variable-length format for positive integers is defined where the high-order bit of each byte indicates whether more bytes remain to be read. The low-order seven bits are appended as increasingly more significant bits in the resulting integer value. Thus values from zero to 127 may be stored in a single byte, values from 128 to 16,383 may be stored in two bytes, and so on.

    VByte Encoding Example

    variable length encoding examples
    Value | Byte 1 | Byte 2 | Byte 3
    --- | --- | --- | ---
    0 | `00000000` |  |
    1 | `00000001` |  |
    2 | `00000010` |  |
    ... |  |  |
    127 | `01111111` |  |
    128 | `10000000` | `00000001` |
    129 | `10000001` | `00000001` |
    130 | `10000010` | `00000001` |
    ... |  |  |
    16,383 | `11111111` | `01111111` |
    16,384 | `10000000` | `10000000` | `00000001`
    16,385 | `10000001` | `10000000` | `00000001`
    ... |  |  |

    This provides compression while still being efficient to decode.

    Parameters:
      `i` - Smaller values take fewer bytes. Negative numbers are supported, but should be avoided.
    Throws:
      `IOException` - If there is an I/O error writing to the underlying medium.
    See Also:
      - `DataInput.readVInt()`

  - ### writeZInt

    public final void writeZInt(int i) throws IOException
    Write a `zig-zag`-encoded `variable-length` integer. This is typically useful to write small signed ints and is equivalent to calling `writeVInt(BitUtil.zigZagEncode(i))`.
    Throws:
      `IOException`
    See Also:
      - `DataInput.readZInt()`

  - ### writeLong

    public void writeLong(long i) throws IOException
    Writes a long as eight bytes (LE byte order).
    Throws:
      `IOException`
    See Also:
      - `DataInput.readLong()`
      - `BitUtil.VH_LE_LONG`

  - ### writeVLong

    public final void writeVLong(long i) throws IOException
    Writes an long in a variable-length format. Writes between one and nine bytes. Smaller values take fewer bytes. Negative numbers are not supported.

    The format is described further in `writeVInt(int)`.

    Throws:
      `IOException`
    See Also:
      - `DataInput.readVLong()`

  - ### writeZLong

    public final void writeZLong(long i) throws IOException
    Write a `zig-zag`-encoded `variable-length` long. Writes between one and ten bytes. This is typically useful to write small signed ints.
    Throws:
      `IOException`
    See Also:
      - `DataInput.readZLong()`

  - ### writeString

    public void writeString(String s) throws IOException
    Writes a string.

    Writes strings as UTF-8 encoded bytes. First the length, in bytes, is written as a `VInt`, followed by the bytes.

    Throws:
      `IOException`
    See Also:
      - `DataInput.readString()`

  - ### copyBytes

    public void copyBytes(DataInput input, long numBytes) throws IOException
    Copy numBytes bytes from input to ourself.
    Throws:
      `IOException`

  - ### writeMapOfStrings

    public void writeMapOfStrings(Map<String,String> map) throws IOException
    Writes a String map.

    First the size is written as an `vInt`, followed by each key-value pair written as two consecutive `String`s.

    Parameters:
      `map` - Input map.
    Throws:
      `NullPointerException` - if `map` is null.
      `IOException`

  - ### writeSetOfStrings

    public void writeSetOfStrings(Set<String> set) throws IOException
    Writes a String set.

    First the size is written as an `vInt`, followed by each value written as a `String`.

    Parameters:
      `set` - Input set.
    Throws:
      `NullPointerException` - if `set` is null.
      `IOException`

  - ### writeGroupVInts

    @Deprecated public void writeGroupVInts(long[] values, int limit) throws IOException
    Deprecated.
    This method is preserved only for backwards codecs
    Encode integers using group-varint. It uses `VInt` to encode tail values that are not enough for a group. we need a long[] because this is what postings are using, all longs are actually required to be integers.
    Parameters:
      `values` - the values to write
      `limit` - the number of values to write.
    Throws:
      `IOException`
    WARNING: This API is experimental and might change in incompatible ways in the next release.

  - ### writeGroupVInts

    public void writeGroupVInts(int[] values, int limit) throws IOException
    Encode integers using group-varint. It uses `VInt` to encode tail values that are not enough for a group.
    Parameters:
      `values` - the values to write
      `limit` - the number of values to write.
    Throws:
      `IOException`
    WARNING: This API is experimental and might change in incompatible ways in the next release.