org.apache.tools.bzip2

## Class CBZip2OutputStream

- java.lang.Object
- - java.io.OutputStream
  - - org.apache.tools.bzip2.CBZip2OutputStream

- All Implemented Interfaces:
    java.io.Closeable, java.io.Flushable, java.lang.AutoCloseable, BZip2Constants

      public class CBZip2OutputStream
      extends java.io.OutputStream
      implements BZip2Constants

  An output stream that compresses into the BZip2 format (without the file header chars) into another stream.

  The compression requires large amounts of memory. Thus you should call the `close()` method as soon as possible, to force `CBZip2OutputStream` to release the allocated memory.

  You can shrink the amount of allocated memory and maybe raise the compression speed by choosing a lower blocksize, which in turn may cause a lower compression ratio. You can avoid unnecessary memory allocation by avoiding using a blocksize which is bigger than the size of the input.

  You can compute the memory usage for compressing by the following formula:

       <code>400k + (9 * blocksize)</code>.

  To get the memory required for decompression by `CBZip2InputStream` use

       <code>65k + (5 * blocksize)</code>.

  Memory usage by blocksize
  Blocksize | Compression memory usage | Decompression memory usage
  --- | --- | ---
  100k | 1300k | 565k
  200k | 2200k | 1065k
  300k | 3100k | 1565k
  400k | 4000k | 2065k
  500k | 4900k | 2565k
  600k | 5800k | 3065k
  700k | 6700k | 3565k
  800k | 7600k | 4065k
  900k | 8500k | 4565k

  For decompression `CBZip2InputStream` allocates less memory if the bzipped input is smaller than one block.

  Instances of this class are not threadsafe.

  TODO: Update to BZip2 1.0.1

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected static int` | `CLEARMASK` This constant is accessible by subclasses for historical purposes.
    `protected static int` | `DEPTH_THRESH` This constant is accessible by subclasses for historical purposes.
    `protected static int` | `GREATER_ICOST` This constant is accessible by subclasses for historical purposes.
    `protected static int` | `LESSER_ICOST` This constant is accessible by subclasses for historical purposes.
    `static int` | `MAX_BLOCKSIZE` The maximum supported blocksize `== 9`.
    `static int` | `MIN_BLOCKSIZE` The minimum supported blocksize `== 1`.
    `protected static int` | `QSORT_STACK_SIZE` This constant is accessible by subclasses for historical purposes.
    `protected static int` | `SETMASK` This constant is accessible by subclasses for historical purposes.
    `protected static int` | `SMALL_THRESH` This constant is accessible by subclasses for historical purposes.
    `protected static int` | `WORK_FACTOR` This constant is accessible by subclasses for historical purposes.

    - ### Fields inherited from interface org.apache.tools.bzip2.BZip2Constants

      `baseBlockSize, G_SIZE, MAX_ALPHA_SIZE, MAX_CODE_LEN, MAX_SELECTORS, N_GROUPS, N_ITERS, NUM_OVERSHOOT_BYTES, rNums, RUNA, RUNB`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `CBZip2OutputStream(java.io.OutputStream out)` Constructs a new `CBZip2OutputStream` with a blocksize of 900k.
    `CBZip2OutputStream(java.io.OutputStream out, int blockSize)` Constructs a new `CBZip2OutputStream` with specified blocksize.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static int` | `chooseBlockSize(long inputLength)` Chooses a blocksize based on the given length of the data to compress.
    `void` | `close()`
    `protected void` | `finalize()` Overridden to close the stream.
    `void` | `finish()`
    `void` | `flush()`
    `int` | `getBlockSize()` Returns the blocksize parameter specified at construction time.
    `protected static void` | `hbMakeCodeLengths(char[] len, int[] freq, int alphaSize, int maxLen)` This method is accessible by subclasses for historical purposes.
    `void` | `write(byte[] buf, int offs, int len)`
    `void` | `write(int b)`

    - ### Methods inherited from class java.io.OutputStream

      `write`

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

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

- - ### Field Detail

    - #### MIN_BLOCKSIZE

          public static final int MIN_BLOCKSIZE

      The minimum supported blocksize `== 1`.
      See Also:
        Constant Field Values

    - #### MAX_BLOCKSIZE

          public static final int MAX_BLOCKSIZE

      The maximum supported blocksize `== 9`.
      See Also:
        Constant Field Values

    - #### SETMASK

          protected static final int SETMASK

      This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
      See Also:
        Constant Field Values

    - #### CLEARMASK

          protected static final int CLEARMASK

      This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
      See Also:
        Constant Field Values

    - #### GREATER_ICOST

          protected static final int GREATER_ICOST

      This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
      See Also:
        Constant Field Values

    - #### LESSER_ICOST

          protected static final int LESSER_ICOST

      This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
      See Also:
        Constant Field Values

    - #### SMALL_THRESH

          protected static final int SMALL_THRESH

      This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
      See Also:
        Constant Field Values

    - #### DEPTH_THRESH

          protected static final int DEPTH_THRESH

      This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
      See Also:
        Constant Field Values

    - #### WORK_FACTOR

          protected static final int WORK_FACTOR

      This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.
      See Also:
        Constant Field Values

    - #### QSORT_STACK_SIZE

          protected static final int QSORT_STACK_SIZE

      This constant is accessible by subclasses for historical purposes. If you don't know what it means then you don't need it.

      If you are ever unlucky/improbable enough to get a stack overflow whilst sorting, increase the following constant and try again. In practice I have never seen the stack go above 27 elems, so the following limit seems very generous.

      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### CBZip2OutputStream

          public CBZip2OutputStream(java.io.OutputStream out)
                             throws java.io.IOException

      Constructs a new `CBZip2OutputStream` with a blocksize of 900k.

      Attention: The caller is responsible to write the two BZip2 magic bytes `"BZ"` to the specified stream prior to calling this constructor.

      Parameters:
        `out` - * the destination stream.
      Throws:
        `java.io.IOException` - if an I/O error occurs in the specified stream.
        `java.lang.NullPointerException` - if `out == null`.

    - #### CBZip2OutputStream

          public CBZip2OutputStream(java.io.OutputStream out,
                            int blockSize)
                             throws java.io.IOException

      Constructs a new `CBZip2OutputStream` with specified blocksize.

      Attention: The caller is responsible to write the two BZip2 magic bytes `"BZ"` to the specified stream prior to calling this constructor.

      Parameters:
        `out` - the destination stream.
        `blockSize` - the blockSize as 100k units.
      Throws:
        `java.io.IOException` - if an I/O error occurs in the specified stream.
        `java.lang.IllegalArgumentException` - if `(blockSize < 1) || (blockSize > 9)`.
        `java.lang.NullPointerException` - if `out == null`.
      See Also:
        `MIN_BLOCKSIZE`, `MAX_BLOCKSIZE`

  - ### Method Detail

    - #### hbMakeCodeLengths

          protected static void hbMakeCodeLengths(char[] len,
                               int[] freq,
                               int alphaSize,
                               int maxLen)

      This method is accessible by subclasses for historical purposes. If you don't know what it does then you don't need it.

    - #### chooseBlockSize

          public static int chooseBlockSize(long inputLength)

      Chooses a blocksize based on the given length of the data to compress.
      Parameters:
        `inputLength` - The length of the data which will be compressed by `CBZip2OutputStream`.
      Returns:
        The blocksize, between `MIN_BLOCKSIZE` and `MAX_BLOCKSIZE` both inclusive. For a negative `inputLength` this method returns `MAX_BLOCKSIZE` always.

    - #### write

          public void write(int b)
                     throws java.io.IOException

      Specified by:
        `write` in class `java.io.OutputStream`
      Throws:
        `java.io.IOException`

    - #### finalize

          protected void finalize()
                           throws java.lang.Throwable

      Overridden to close the stream.
      Overrides:
        `finalize` in class `java.lang.Object`
      Throws:
        `java.lang.Throwable`

    - #### finish

          public void finish()
                      throws java.io.IOException

      Throws:
        `java.io.IOException`

    - #### close

          public void close()
                     throws java.io.IOException

      Specified by:
        `close` in interface `java.io.Closeable`
      Specified by:
        `close` in interface `java.lang.AutoCloseable`
      Overrides:
        `close` in class `java.io.OutputStream`
      Throws:
        `java.io.IOException`

    - #### flush

          public void flush()
                     throws java.io.IOException

      Specified by:
        `flush` in interface `java.io.Flushable`
      Overrides:
        `flush` in class `java.io.OutputStream`
      Throws:
        `java.io.IOException`

    - #### getBlockSize

          public final int getBlockSize()

      Returns the blocksize parameter specified at construction time.

    - #### write

          public void write(byte[] buf,
                   int offs,
                   int len)
                     throws java.io.IOException

      Overrides:
        `write` in class `java.io.OutputStream`
      Throws:
        `java.io.IOException`