Decompression

.classpath

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-14">
+		<attributes>
+			<attribute name="module" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="output" path="bin"/>
+</classpath>

.project

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>LZWDecompression</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+	</natures>
+</projectDescription>

TestFile

@@ -0,0 +1 @@
+c*$�����
#&

TestFile2

@@ -0,0 +1 @@
+abcabcabcabc

bin/.gitignore

@@ -0,0 +1,4 @@
+/LZW.class
+/LZWDecoder.class
+/TestFile
+/Tester.class

LZW.java → src/LZW.java

@@ -1,6 +1,9 @@
 import java.io.*;
+//little change;
+
 import java.util.*;
 
+
 public class LZW {
 
     private static final int BIT_0 = 1;
@@ -36,6 +39,8 @@ public LZW(int BinaryLength, String newFileName)
         newFilename = newFileName;
         map = new HashMap<String, String>((int)Math.pow(2, binaryLength));
         binaryLength = BinaryLength;
+
+        //filling first 255 elements in the dictionary.
         for(int i = 0; i < 256; i++)
         {
             String binString = intToBinary(i);
@@ -45,7 +50,7 @@ public LZW(int BinaryLength, String newFileName)
         }
     }
 
-    public void encode(String filepath) throws IOException
+    public String encode(String filepath) throws IOException
     {
         int counter = 256;
 
@@ -88,6 +93,7 @@ else if(nextInt == -1)
         }
 
         writeToBinary(sb.toString());
+        return (sb.toString());
 
     }
 
@@ -109,6 +115,7 @@ public static void writeToBinary(String s) throws IOException
 
         FileOutputStream fos = new FileOutputStream(newFilename);
         fos.write(l_raw);
+        fos.close();
     }
 
     public static String intToBinary(int num)
@@ -122,10 +129,5 @@ public static String intToBinary(int num)
         return binString;
     }
 
-    public static void main(String[] args) throws IOException {
-        // TODO Auto-generated method stub
-        LZW lzw = new LZW(9, "output.bin");
 
-        lzw.encode("lzw-file3.txt");
-    }
 }

src/LZWDecoder.java

@@ -0,0 +1,137 @@
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.PrintWriter;
+import java.util.HashMap;
+
+public class LZWDecoder {
+
+	private HashMap <Integer, String> dict;
+	private int bitNum;
+	private String binString;
+	private byte [] byteArray;
+	private String finalOutput;
+
+	public LZWDecoder(String binString, int bitNum, String outputFileName) throws IOException
+	{
+		this.dict = new HashMap <Integer, String>();
+		this.bitNum = bitNum;
+		this.binString = binString;
+		this.finalOutput = "";
+
+
+//		File binFile = new File (binFileName);
+//		readBinFile(binFile);
+		decode();
+		writeToTxt(outputFileName);
+
+	}
+
+	//reads the binary file into a string. not working, so I've bypassed this method for now and just input a binary string into the constructor.
+	public void readBinFile(File binFile) throws IOException
+	{
+		FileInputStream is = new FileInputStream(binFile);
+
+		int currInt = is.read();
+		while (currInt != -1)
+		{
+			binString+=currInt;
+		}
+		is.close();
+	}
+
+
+
+	public void decode ()
+	{
+		for (int x = 0; x<256; x++)
+		{
+			char ch = (char)x;
+			dict.put(x, String.valueOf(ch));
+		}
+		String binStringCopy = binString;
+		String currBinString = binString.substring (0,bitNum);
+		binString= binString.substring(bitNum);
+		int currDecimal = Integer.parseInt(currBinString, 2);
+		String currString = dict.get(currDecimal);
+//		finalOutput = currString;
+
+		String nextBinString = "";
+		int nextDecimal= 0;
+		String nextString= "";
+
+//		String lastSymbolInDict = "";
+
+		nextBinString = binString.substring(0, bitNum);
+		binString= binString.substring(bitNum);
+		nextDecimal = Integer.parseInt(nextBinString, 2);
+		nextString = dict.get(nextDecimal);
+
+		int counter = 256;
+		while (binString.length()>= bitNum)
+		{
+
+			if (nextString!= null)
+			{
+				dict.put(counter, currString+ nextString.substring(0,1));
+				currString = nextString;
+
+
+
+			}
+			else
+			{
+				dict.put(counter, currString + currString.substring(0,1));
+				currString = currString + currString.substring(0,1);
+			}
+
+			nextBinString = binString.substring(0, bitNum);
+			binString= binString.substring(bitNum);
+			nextDecimal = Integer.parseInt(nextBinString, 2);
+			nextString = dict.get(nextDecimal);
+
+			counter++;
+		}
+
+		for (int x = 0; x<binStringCopy.length()/bitNum;x++)
+		{
+			String currBinStringCopy = binStringCopy.substring(0,bitNum);
+			binStringCopy= binStringCopy.substring(bitNum);
+			finalOutput+=dict.get(Integer.parseInt(currBinStringCopy, 2));
+		}
+	}
+
+	//writes the 
+	public void writeToTxt(String outputFileName) throws FileNotFoundException
+	{
+		PrintWriter output = new PrintWriter(outputFileName);
+		output.print (finalOutput);
+		output.close();
+	}
+
+//	class GFG {
+//		 
+//	    // Function to convert binary to decimal
+//	    private static int binaryToDecimal (String n)
+//	    {
+//	        String num = n;
+//	        int dec_value = 0;
+//	 
+//	        // Initializing base value to 1,
+//	        // i.e 2^0
+//	        int base = 1;
+//	 
+//	        int len = num.length();
+//	        for (int i = len - 1; i >= 0; i--) {
+//	            if (num.charAt(i) == '1')
+//	                dec_value += base;
+//	            base = base * 2;
+//	        }
+//	 
+//	        return dec_value;
+//	    }
+
+}
+

src/Tester.java

@@ -0,0 +1,13 @@
+import java.io.IOException;
+
+public class Tester {
+    public static void main(String[] args) throws IOException {
+        LZW compressor = new LZW(9, "TestFile");
+
+        String testString = compressor.encode("lzw-file1.txt");
+        System.out.println (testString);
+
+        LZWDecoder expander = new LZWDecoder (testString, 9, "TestFile2");
+
+    }
+}