当我使用长度为 256 的符号表（字典）时，我的 LZW 压缩工作，编码器和解码器都使用 256 并且一切正常，但是当我将这个数字增加到 512、1024、4096 时，解码的文件输出不一样与第一个输入文件...任何提示？
源代码：
LZWEncoder.java：
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)+"\n").getBytes();
// writer.write(size_stInBytes);
System.out.println("File size " + file_size + " Sysmbol tree " + size_st);
// input stream with lookahead
LookAheadIn in = new LookAheadIn ( file );
LZWst st = new LZWst (4096); // specialised ST
while (! in.isEmpty ())
{
int codeword = st.getput (in );
writer.write ( codeword );
}
writer.close ();
reader.close ();
}
}
LZWDecoder.java：
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) // Tricky situation !
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.java：
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
{ // standard node code
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; // EOF
roots [c] = getput (c, roots [c],in );
in. backup ();
return codeword ; // longest prefix
}
public Node getput ( int c, Node x, LookAheadIn in)
throws FileNotFoundException , IOException
{ // recursive search *and* insert
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.java：
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; }
}