Requirement: Implement encoder and decoder for LZW compression algorithms using

Question

Requirement: Implement encoder and decoder for LZW compression algorithms using JAVA.

Encoder:   
1. Input: A file and parameters for your compression algorithm if applicable.

2. Output: A file which is the compressed version of the input file.

3. Readme and Makefile for encoder.
Decoder:   
1. Input: The compressed file generated by the encoder.

2. Output: A file which should be the same as the original file compressed by the encoder.

3. Readme and Makefile for decoder.

Testing:
1. Use five different types of files (The size of each file should be at least 1MB.) to test your encoder and decoder. Provide one script file for encoding the five files and one script file for decoding the five compressed files.

2. Use one of other popular compression tools, winzip, to compress the five files.

3. Create an Excel figure to compare compression ratios of 1 and 2. 4. Readme and script files for testing.

Explanation / Answer

LZWEncoder

import java .io .*;
public class LZWEncoder
{
public static void main ( String [] args )
throws FileNotFoundException , IOException
{
File file = new File ("calgary/book1");
File fileOut = new File ( "calgary/book1_enc");
FileInputStream reader = new FileInputStream ( file );
FileOutputStream writer = new FileOutputStream ( fileOut );
int size_st;
long file_size;
file_size = file.length();
size_st = (int) file_size/1024;
System.out.println("File size " + file_size + " Sysmbol tree" + size_st);

if (size_st < 256)
size_st = 256;
else if (size_st < 512)
size_st = 512;
else if (size_st < 1024)
size_st = 1024;
else if (size_st < 2048)
size_st = 2048;
else
size_st = 4096;

byte[] size_stInBytes = (Integer.toString(size_st)+" ").getBytes();
  
System.out.println("File size " + file_size + " Sysmbol tree " + size_st);

  
LookAheadIn in = new LookAheadIn ( file );
LZWst st = new LZWst (4096);
while (! in.isEmpty ())
{
int codeword = st.getput (in );
writer.write ( codeword );
}
writer.close ();
reader.close ();
}
}

LZWDecoder

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Scanner;

public class LZWDecoder
{
public static void main ( String [] args )
throws FileNotFoundException , IOException
{
File file = new File ("calgary/book1_enc");
Scanner first_line = new Scanner("calgary/book1_enc");
File fileOut = new File ( "calgary/book1_dec2");
FileInputStream reader = new FileInputStream ( file );
FileOutputStream writer = new FileOutputStream ( fileOut );
String size_st;
size_st =first_line.nextLine();
System.out.println(" Sysmbol tree " + size_st);
String [] st = new String [4096];
int i;
for (i=0; i <128; i++)
st[i] = Character.toString (( char ) i);

String prev = "";
int codeword ;
while (( codeword = reader.read())!= -1)
{

String s;
if ( codeword == i)
s = prev + prev.charAt(0);
else
s = st[codeword ];
for (int j = 0; j<s.length(); j++)
writer.write(s.charAt (j));
if ( prev.length() > 0 && i < 4096 )
st[i++] = prev + s.charAt(0);
prev = s;
}
writer.close();
reader.close();
}
}

LZWst:-

import java.io.FileNotFoundException;
import java.io.IOException;

public class LZWst
{
private int i; // next codeword to assign
private int codeword ; // codeword to return
private Node [] roots ; // array of TSTs
private int st_size;
public LZWst (int st_sz)
{
st_size = st_sz;
roots = new Node [128];
for (i=0; i <128; i++) // init with ASCII
roots [i] = new Node (( char ) i,i);
}
private class Node
{
Node (int c, int codeword )
{
this .c = c;
this . codeword = codeword ;
}
int c;
Node left , mid , right ;
int codeword ;
}

public int getput ( LookAheadIn in)
throws FileNotFoundException , IOException
{
int c = in. readChar ();
if ( c == -1) return -1;
roots [c] = getput (c, roots [c],in );
in. backup ();
return codeword ;
}
public Node getput ( int c, Node x, LookAheadIn in)
throws FileNotFoundException , IOException
{
if (x== null ) {
if (i<st_size){
x = new Node (c,i++);
System.out.println("Value of i: " + i);
}
return x;
}
if (c<x.c) x. left = getput (c,x.left ,in );
else if (c>x.c) x. right = getput (c,x.right ,in );
else {
int next = in.readChar();
codeword = x. codeword ;
x.mid = getput (next ,x.mid ,in );
}
return x;
}
}

LookAheadIn:-

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

public class LookAheadIn
{
private FileInputStream in = null ;
private int last ;
private boolean backup = true ;
public LookAheadIn ( File file )
throws FileNotFoundException , IOException
{
in = new FileInputStream ( file );
last = in. read ();
backup = true ;
}
public void backup () { backup = true ; }
public int readChar () throws FileNotFoundException , IOException
{
if (! backup ) last = in. read();
backup = false ;
return last ;}
public boolean isEmpty(){ return last == -1; }
}

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