java实现的LZW 压缩算法源码

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/*
 * LZW.java
 *
 * Created on 01 Dec 2005
 *
 * Implementation of LZW compression/decompression algorithm
 */
import java.io.* ;
/**
 *
 * @author  Moshe Fresko
 * @course Algorithmic Programming 1
 * @exercise 3
 */
public class LZW implements Compression
{
 boolean stopped = false ;
 Dict dict ;
  // The bits that should be written for each code
 int numOfBits ;
  // The previous string that we should remember
  // in order to insert into the dictionary
 final ByteArray emptyBA = new ByteArray() ;
 ByteArray w=emptyBA ;
  // Constructor gets the number of bits to be written for each code
 public LZW()
 {
  numOfBits = 12 ;
   // Create a new Limited Dictionary
   // For maximum of 2^bits entries
  dict = new LimitedDict(1<< umOfBits) ;
   // Add all ascii characters to the dictionary
  for (int i=0;i<256;++i)
   dict.add(new ByteArray((byte)i)) ;
 }
  // Encodes the next character.
  // If there is a code generated returns it.
  // If not returns -1.
 int encodeOneChar(int n) {
  byte c = (byte) n ;
  ByteArray nw = w.conc(c) ;
  int code = dict.numFromStr(nw) ;
   // if it exists then we continue to search for a longer string
  if (code!=-1) {
   w = nw ;
   return -1 ;
  } else {
   dict.add(nw) ;
   nw = w ;
   w = new ByteArray(c) ;
   return dict.numFromStr(nw) ;
  }
 }
  // If there is something left in w, returns its code
 int encodeLast() {
  ByteArray nw = w ;
  w = emptyBA ;
  return dict.numFromStr(nw) ;
 }
  // Write the code in bits into output stream
 void writeCode(OutputStream os, int code) throws IOException
 {
  for (int i=0;i< numOfBits;++i) {
   os.write(code&1) ;
   code /= 2 ;
  }
 }
 int readCode(InputStream is) throws IOException
 {
  int num = 0 ;
  for (int i=0;i< numOfBits;++i) {
   int next = is.read() ;
   if (next<0)
    return -1 ;
   num += next<< i ;
  }
  return num ;
 }
  // We need to call the close() method of BitOutputStream,
  // but without closing the encompassing OutputStream
 private class UnClosedOutputStream extends FilterOutputStream {
  public UnClosedOutputStream(OutputStream os)
   { super(os) ; }
    public void write(byte b[], int off, int len) throws IOException
     { out.write(b,off,len) ; }
     // Does not close anything
  public void close() throws IOException
   { }
 }
 public void compress(InputStream is, OutputStream os) throws IOException {
  os = new BitOutputStream(new UnClosedOutputStream(os)) ;
  int next ; // next input character
  int code ; // next code generated
  while ((next=is.read())>=0) {
   if (stopped)
    break ;
   code = encodeOneChar(next) ;
   if (code>=0)
    writeCode(os,code) ;
  }
  code = encodeLast() ;
  if (code>=0)
   writeCode(os,code) ;
    os.close() ;
 }
 ByteArray decodeOne(int code) {
   // Either "ABA" or null, w="AB"
  ByteArray str = dict.strFromNum(code) ;
  if (str==null) {
   str = w.conc(w.getAt(0)) ;
   dict.add(str) ;
  } else
   if (! w.isEmpty())
    dict.add(w.conc(str.getAt(0))) ;
            w = str ;
  return w ;
 }
 public void decompress(InputStream is, OutputStream os) throws IOException {
  is = new BitInputStream(is) ;
  ByteArray str ; // Next entry
  int code ;  // Next code to be read
  while ((code=readCode(is))>=0) {
   if (stopped)
    break ;
   str = decodeOne(code) ;
   os.write(str.getBytes()) ;
  }
 }
 public void stop()
  { stopped = true ; }
       public static void main(String args[]){//简单的测试
          LZW lzw=new LZW();
          try{
            lzw.compress(new FileInputStream("LZW.JAVA"),new FileOutputStream("lzw.lzw"));
            lzw.decompress(new FileInputStream("lzw.lzw"),new FileOutputStream("lzw1.java"));
          }catch(Exception e){}
       }
}

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http://www.java3z.com/cwbwebhome/article/article3/3298.html?id=1044             

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