ch.rgw.compress
Class Huff

java.lang.Object
  ch.rgw.compress.Huff

public class Huff
extends java.lang.Object

Simple implementation of the Huffman compression algorithm. Consists solely of static functions.
To compress data:

1. Load, create or use a frequency table for the data to compress: (Tree.constructTable(), Tree.loadTable(), Tree.useTable())
2. Create a Huffman tree and obtain its root Node: new Tree().build(table);
3. compress the data: encode()
4. expand the data: decode()

This implementation uses an extension to the straightforward algorithm to deal with the situation of a character being written, which was not in the table, and with end-of-file conditions. In such cases, an escape character (0x07) will be written and specially interpreted

Author:

Gerry

Field Summary

static int	eof
static byte	escape

Constructor Summary

Huff()


Method Summary

static byte[]	decode(HuffmanTree tree, byte[] source) Huffman decode the source array
static java.lang.String	decodeString(HuffmanTree tree, byte[] in) Decode a previously with encodeString compressed String
static byte[]	encode(HuffmanTree tree, byte[] source) Huffman encode the source array
static byte[]	encodeString(HuffmanTree tree, java.lang.String i) Huffman encode a String
static void	main(java.lang.String[] argv) The main function can be used to accomplish a few tasks regarding persistent storage of Huffman tables.: java -classpath . ch.rgw.tools.Compress.Huff list: shows all stored tables in the system Preferences java -classpath . ch.rgw.tools.Compress.Huff create : computes a frequency table of the and stores ist as in the preferences.
static java.lang.String	Version()
static void	writeEOF(ch.rgw.compress.HuffmanTree.Node act, BitOutputStream out)

Methods inherited from class java.lang.Object

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

Field Detail

escape

public static final byte escape

See Also:

Constant Field Values

eof

public static final int eof

See Also:

Constant Field Values

Constructor Detail

Huff

public Huff()

Method Detail

Version

public static java.lang.String Version()

encode

public static byte[] encode(HuffmanTree tree,
                            byte[] source)

Huffman encode the source array

Parameters:

tree - a Hufmann tree as created by new Tree() or null

source - the source to compress. If tree is null, the Tree will be computed from the source first and its frequency table is included in the output.

Returns:

The huffman compressed source

decode

public static byte[] decode(HuffmanTree tree,
                            byte[] source)

Huffman decode the source array

Parameters:

tree - a Huffman tree as created by new Tree() or null

source - A huffman compressed array as returned by encode(). If tree is null, the frequency count is expected to be included to the source.

Returns:

the decoded data or null on error.

encodeString

public static byte[] encodeString(HuffmanTree tree,
                                  java.lang.String i)

Huffman encode a String

decodeString

public static java.lang.String decodeString(HuffmanTree tree,
                                            byte[] in)

Decode a previously with encodeString compressed String

writeEOF

public static void writeEOF(ch.rgw.compress.HuffmanTree.Node act,
                            BitOutputStream out)
                     throws java.io.IOException

Throws:

java.io.IOException

main

public static void main(java.lang.String[] argv)

The main function can be used to accomplish a few tasks regarding persistent storage of Huffman tables.:

• java -classpath . ch.rgw.tools.Compress.Huff list: shows all stored tables in the system Preferences
• java -classpath . ch.rgw.tools.Compress.Huff create : computes a frequency table of the and stores ist as in the preferences.
• java -classpath . ch.rgw.tools.Compress.Huff export : exports the table from the preferences into two files:
  • .bin: A binary representation (sequence of bytes)
  • .asc: A textual representation (comma separated list)