Made a decoder class

.classpath

@@ -1,10 +1,6 @@
 <?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="con" path="org.eclipse.jdt.launching.JRE_CONTAINER"/>
 	<classpathentry kind="src" path="src"/>
 	<classpathentry kind="output" path="bin"/>
 </classpath>

.project

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <projectDescription>
-	<name>LZWCompression</name>
+	<name>LZW-Compression</name>
 	<comment></comment>
 	<projects>
 	</projects>

ReadMe

@@ -5,4 +5,9 @@ uses the method fillInitialValues() to fill the HashMap dict with the pre-determ
 It then calls the method compress which uses a buffered reader and a for loop to run through each char in the file. 
 It adds combinations of these chars with arbitrary, decimal askii values to dict. The for loop also converts these 
 decimals to binary before adding them to the string binaryString. binaryString is converted into a char array of 0s and 1s, 
-which is then converted to a byte array, which is then used by the FileOutputStream to write a binary file. 
+which is then converted to a byte array, which is then used by the FileOutputStream to write a binary file. 
+
+ROHAN: Ariana used 9 bits
+The decoder does not work, I am unsure if it is an issue with the decoder or your encoder
+It outputs something for file 1, but it is not right 
+It gets an error for file 3 

decoded.txt

@@ -0,0 +1 @@
+Æ888HHH(```d

src/RohanDecoder.java

@@ -0,0 +1,143 @@
+import java.util.*;
+
+import java.io.*;
+import java.nio.file.*;
+
+public class RohanDecoder {
+
+	public HashMap<Integer, String> dictionary;
+	public String binary;
+	int binaryIndex;
+	ArrayList<Integer> numberValues;
+
+	public RohanDecoder() {
+		binary = "";
+		dictionary = new HashMap<Integer, String>();
+		this.makeDictionary();
+	}
+
+	public void makeDictionary() { 
+		for(int i = 0; i<256; i++) {
+			dictionary.put(i, "" + (char)i);
+		}
+	}
+
+	public void ByteToBinary() throws IOException {
+		 FileInputStream input = new FileInputStream("trashbin");
+
+	     binary = ""; 
+	     byte[] byteArray = input.readAllBytes();
+	     //System.out.println(byteArray);
+
+	     for(int i =0;i<byteArray.length;i++)
+			{
+				//System.out.println(byteArray[i]+" "+toBinary(byteArray[i]));
+
+				binary+= this.toBinary(byteArray[i]);
+				//System.out.println(binary);
+			}
+	     input.close();
+
+	}
+
+	public void decode() throws IOException { //algorithm from https://www.geeksforgeeks.org/lzw-lempel-ziv-welch-compression-technique/
+		this.ByteToBinary();
+		PrintWriter outputWriter = new PrintWriter(new BufferedWriter(new FileWriter("decoded.txt")));
+
+		binaryIndex = 0;
+
+		this.makeNumbersFromBinary(); //fills the variable numberValues with the number representations of each 9 bit binary string
+		//System.out.println(this.numberValues);
+
+		Integer old = numberValues.get(0);
+		outputWriter.print(dictionary.get(old)); //outputs the value from old
+
+		int nextDictIndex = 256;
+		String combination = dictionary.get(old);
+		String firstLetter = "" + combination.charAt(0);
+
+
+		for(int i = 1; i< numberValues.size(); i+=1) {
+			Integer newest = numberValues.get(i);
+
+			if(dictionary.containsKey(newest)) {
+				combination = dictionary.get(newest); //if it contains newest then we set the combo to its value
+			}
+			else {
+				combination = dictionary.get(old); //if it doenst contain newest, then we set combo to old + firstLetter
+				combination = combination + firstLetter;
+			}
+
+			outputWriter.print(combination);
+
+			firstLetter = "" + combination.charAt(0);
+			dictionary.put(nextDictIndex, dictionary.get(old) + combination);
+			nextDictIndex+=1;
+			old = newest;
+		}
+
+		outputWriter.close();
+//		System.out.println(old);
+//		System.out.println(dictionary.get(old));
+
+
+//		String Binary2 = binary.substring(9,18);
+//		System.out.println("binary " + oldBinary);
+//		System.out.println("binary " + Binary2);
+	}
+
+
+	public Integer getNextNumberFromBinary() {
+
+		String nextBinary = this.binary.substring(this.binaryIndex, this.binaryIndex+9);
+		binaryIndex+=9;
+		return Integer.parseInt(nextBinary,2);
+	}
+
+	public void makeNumbersFromBinary() {
+		this.numberValues = new ArrayList<Integer>();
+
+		for(int i = 0;i <= binary.length() - 9; i+=9) {
+//			System.out.println("next number = " + this.getNextNumberFromBinary());
+//			System.out.println("list =  " + this.numberValues);
+			//System.out.println(dictionary.get(this.getNextNumberFromBinary()));
+			//numberValues.add(getNextNumberFromBinary());
+//			if(i+9 > binary.length()) {
+//				break;
+//			}
+
+			numberValues.add(binaryToNumber(binary.substring(i,i+9)));
+		}
+	}
+
+	public static int binaryToNumber(String a) //found online
+	{
+		int ans = 0;
+		for(int i = 0;i<9;i++)
+		{
+			if(a.charAt(i)=='1')
+			{
+				ans+=(1<<(8-i));
+			}
+		}
+		return ans;
+	}
+
+
+
+	public String toBinary(int number)
+	{
+		String cur =Integer.toBinaryString(number);
+		StringBuilder ans = new StringBuilder();
+		while(cur.length()+ans.length()<8)
+		{
+			ans.append("0");
+		}
+		if(cur.length()>8)
+		{
+			cur = cur.substring(cur.length()-8);
+		}
+		ans.append(cur);
+		return ans.toString();
+	}
+}

src/TestLZW.java

@@ -7,5 +7,8 @@ public static void main (String [] args) throws IOException
 		File testFile = new File ("lzw-file1.txt");
 		LZWCompression compressy= new LZWCompression (testFile);
 
+		RohanDecoder decode = new RohanDecoder();
+		decode.decode();
+
 	}
 }