net.siefkes.nlstego.textgen
Class StegoCoder

java.lang.Object
  net.siefkes.nlstego.textgen.StegoCoder

Direct Known Subclasses:

StegoDecoder, StegoEncoder

public class StegoCoder
extends Object

Base class that contains common code shared by the StegoEncoder and StegoDecoder classes.

Instances of this class are not stateless and must be synchronized externally, if required.

Version:

$Revision: 1.12 $, $Date: 2005/07/28 15:03:12 $, $Author: siefkes $

Author:

Christian Siefkes

Constructor Summary

StegoCoder(Configuration conf, TextModel model)
Creates a new instance.

Method Summary

protected void	debugBits(int num0, boolean added1, int predIndex, int predCount, String token) Adds a debug statement that allows tracing the encoding/decoding of bits.
protected void	debugSingleton(String token) Adds a debug statement that allows tracing the occurrence of single-element prediction lists.
protected List<PredictedToken>	filterFirst(List<PredictedToken> predictions) This method is called during encoding and decoding to filter unsuitable predictions for the very first token in a stego text.
protected TextModel	getTextModel() Returns the text model used by this instance.
protected void	resetState() Resets the state of this instance, to start encoding/decoding a new text sequence.
String	toString() Returns a string representation of this object.
protected void	updateState(String token) Updates the state of a text model after choosing a token.

Methods inherited from class java.lang.Object

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

Constructor Detail

StegoCoder

public StegoCoder(Configuration conf,
                  TextModel model)

Creates a new instance.

Parameters:

conf - the configuration to use

model - the text model to use

Method Detail

debugBits

protected void debugBits(int num0,
                         boolean added1,
                         int predIndex,
                         int predCount,
                         String token)

Adds a debug statement that allows tracing the encoding/decoding of bits. This method should only be called if debugging is enabled for NLStego.LOG.

Parameters:

num0 - the number of '0' bits

added1 - whether a '1' bit followed

predIndex - the index of the current prediction

predCount - the number of active predictions

token - the predicted token

debugSingleton

protected void debugSingleton(String token)

Adds a debug statement that allows tracing the occurrence of single-element prediction lists. This method should only be called if debugging is enabled for NLStego.LOG.

Parameters:

token - the predicted token

filterFirst

protected List<PredictedToken> filterFirst(List<PredictedToken> predictions)

This method is called during encoding and decoding to filter unsuitable predictions for the very first token in a stego text. It discards any predicted tokens not starting with whitespace to avoid confusion between tokens with and without initial whitespace.

Parameters:

predictions - the original list of likely predictions

Returns:

a filters list of predictions suitable for the very first token

getTextModel

protected TextModel getTextModel()

Returns the text model used by this instance.

Returns:

the value of the attribute

resetState

protected void resetState()

Resets the state of this instance, to start encoding/decoding a new text sequence.

updateState

protected void updateState(String token)

Updates the state of a text model after choosing a token.

Parameters:

token - the chosen token

toString

public String toString()

Returns a string representation of this object.

Overrides:

toString in class Object

Returns:

a textual representation