LZ77.java

import java.io.*;

/**
 * Class for performing LZ77 compression/decompression using text IO
 *
 * @author Mark Hall
 * @version 1.0
 */
public class LZ77T {
  public static final int DEFAULT_BUFF_SIZE = 1024;
  protected int mBufferSize;
  protected Reader mIn;
  protected PrintWriter mOut;
  protected StringBuffer mSearchBuffer; 

  public LZ77T() {
    this(DEFAULT_BUFF_SIZE);
  }
  
  public LZ77T(int buffSize) {
    mBufferSize = buffSize;
    mSearchBuffer = new StringBuffer(mBufferSize);
  }

  private void trimSearchBuffer() {
    if (mSearchBuffer.length() > mBufferSize) {
      mSearchBuffer = 
  mSearchBuffer.delete(0,  mSearchBuffer.length() - mBufferSize);
    }
  }

  /**
   * Uncompress method
   *
   * @param infile the name of the file to uncompress - automatically appends
   * a ".lz77" extension to the supplied filename
   * @exception IOException if an error occurs during file processing
   */
  public void unCompress(String infile) throws IOException {
    mIn = new BufferedReader(new FileReader(infile+".lz77"));
    StreamTokenizer st = new StreamTokenizer(mIn);

    st.ordinaryChar((int)' ');
    st.ordinaryChar((int)'.');
    st.ordinaryChar((int)'-');
    st.ordinaryChar((int)'\n');
    st.wordChars((int)'\n', (int)'\n');
    st.wordChars((int)' ', (int)'}');

    int offset, length;
    while (st.nextToken() != StreamTokenizer.TT_EOF) {
      switch (st.ttype) {
      case StreamTokenizer.TT_WORD:
	mSearchBuffer.append(st.sval);
	System.out.print(st.sval);
	// Adjust search buffer size if necessary
	trimSearchBuffer();
	break;
      case StreamTokenizer.TT_NUMBER:
	offset = (int)st.nval; // set the offset
	st.nextToken(); // get the separator (hopefully)
	if (st.ttype == StreamTokenizer.TT_WORD) {
	  // we got a word instead of the separator,
	  // therefore the first number read was actually part of a word
	  mSearchBuffer.append(offset+st.sval);
	  System.out.print(offset+st.sval);
	  break; // break out of the switch
	}
	// if we got this far then we must be reading a
	// substitution pointer
	st.nextToken(); // get the length
	length = (int)st.nval;
	// output substring from search buffer
	String output = mSearchBuffer.substring(offset, offset+length);
	System.out.print(output);
	mSearchBuffer.append(output);
	// Adjust search buffer size if necessary
	trimSearchBuffer();
	break;
      default:
	// consume a '~'
      }
    }
    mIn.close();
  }

  /**
   * Compress method
   *
   * @param infile the name of the file to compress. Automatically appends
   * a ".lz77" extension to infile name when creating the output file
   * @exception IOException if an error occurs
   */
  public void compress(String infile) throws IOException {
    // set up input and output
    mIn = new BufferedReader(new FileReader(infile));
    mOut = new PrintWriter(new BufferedWriter(new FileWriter(infile+".lz77")));

    int nextChar;
    String currentMatch = "";
    int matchIndex = 0, tempIndex = 0;

    // while there are more characters - read a character
    while ((nextChar = mIn.read()) != -1) {
      // look in our search buffer for a match
      tempIndex = mSearchBuffer.indexOf(currentMatch + (char)nextChar);
      // if match then append nextChar to currentMatch
      // and update index of match
      if (tempIndex != -1) {
	currentMatch += (char)nextChar;
	matchIndex = tempIndex;
      } else {
	// found longest match, now should we encode it?
	String codedString = 
	  "~"+matchIndex+"~"+currentMatch.length()+"~"+(char)nextChar;
	String concat = currentMatch + (char)nextChar;
	// is coded string shorter than raw text?
	if (codedString.length() <= concat.length()) {
	  mOut.print(codedString);
	  mSearchBuffer.append(concat); // append to the search buffer
	  currentMatch = "";
	  matchIndex = 0;
	} else {
	  // otherwise, output chars one at a time from
	  // currentMatch until we find a new match or
	  // run out of chars
	  currentMatch = concat; matchIndex = -1;
	  while (currentMatch.length() > 1 && matchIndex == -1) {
	    mOut.print(currentMatch.charAt(0));
	    mSearchBuffer.append(currentMatch.charAt(0));
	    currentMatch = currentMatch.substring(1, currentMatch.length());
	    matchIndex = mSearchBuffer.indexOf(currentMatch);
	  }
	}
	// Adjust search buffer size if necessary
	trimSearchBuffer();
      }
    }
    // flush any match we may have had when EOF encountered
    if (matchIndex != -1) {
      String codedString = 
	"~"+matchIndex+"~"+currentMatch.length();
      if (codedString.length() <= currentMatch.length()) {
	mOut.print("~"+matchIndex+"~"+currentMatch.length());
      } else {
	mOut.print(currentMatch);
      }
    }
    // close files
    mIn.close();
    mOut.flush(); mOut.close();
  }
  
  public static void main(String [] args) {
    if (args.length < 2) {
      System.err.println("Usage: LZ77T [c|d] <filename>");
      System.exit(1);
    }
    LZ77T lz = new LZ77T();
    try {
      if (args[0].indexOf('d') != -1) {
	lz.unCompress(args[1]);
      } else {
	lz.compress(args[1]);
      }
    } catch (FileNotFoundException f) {
      System.err.println("File not found: "+args[0]);
    } catch (IOException e) {
      System.err.println("Problem processing file: "+args[0]);
    }
  }
}

How do i input the file into the program...
Im using BlueJ but im not sure how i compress a file