Cipher and Decipher: Out of Bounds Exception

[Christopher Goad]

Okay I am currently stuck and have not been able to get past this assignment in my Computer Science Class. My program has to create a randomly generated alphabet then cipher a message. Both the alphabet and message are then printed to a text file. Part 2 of it has reading the random alphabet and decoding the message. My encryption class works fine but the decryption class is the killer. If you could help it would be greatly appreciated. The project folder and assignment instructions are attached.

/**
* This class tests CaesarShiftEncryption and CaesarShiftDecryption classes
*
* @author Christopher Goad
* @version 3-13-12
*/

import java.io.File;
import java.util.Scanner;
import java.util.ArrayList;
import java.io.IOException;
import java.io.PrintWriter;
public class ChrisGoadCipherTester
{
    //constant for the alphabet
    public static ArrayList<Character> alphabet = makeAlphabet();
   
    public ChrisGoadCipherTester()
    {
    }
   
    public static ArrayList<Character> makeAlphabet()
    {
        ArrayList<Character> alphabet = new ArrayList<Character>();
        int letter = 65;
        for (int loop = 0; loop < 26; loop++)
        {
            alphabet.add((char)letter);
            letter++;
        }
        return alphabet;
    }
    
    public static void main(String[] args) throws IOException
    {
        Scanner in = new Scanner(System.in);
        //Menu for the user
        System.out.println("===============================");
        System.out.println("     [A] Chris Goad Cipher ");
        System.out.println("     [B] Chris Goad Decipher ");
        System.out.println("           [Q] Quit           ");
        System.out.println("===============================");
        System.out.print("Please select an letter option from the above menu and hit enter: ");
       
        String input = in.next();
        if (input.equalsIgnoreCase("A"))
        {
            ChrisGoadCipher.getInput();
        }
        else if (input.equalsIgnoreCase("B"))
        {
            ChrisGoadDecipher.getInput();
        }
        else if (input.equalsIgnoreCase("Q"))
        {
            System.out.println("You chose to quit. Goodbye!");
        }
        else
        {
            System.out.println("You did not choose a vaild option.");
        }
    }
}

 /**
* This class is used to encrypt messages with a Caesar shift number.
*
* @author Christopher Goad
* @version 3-13-12
*/

import java.io.File;
import java.util.Scanner;
import java.util.ArrayList;
import java.io.IOException;
import java.io.PrintWriter;
public class ChrisGoadCipher
{
    private static ArrayList<Character> newAlphabet = new ArrayList<Character>();
    private static ArrayList<Character> alphabet = ChrisGoadCipherTester.alphabet;
    
    public ChrisGoadCipher()
    {   
        
    }
   
    public static void getInput() throws IOException
    {
        //Ask for user input and call required methods
        Scanner in = new Scanner(System.in);
        createNewAlphabet();
        System.out.println("Here is the alphabet being used for encryption:");
        displayNewAlphabet(newAlphabet);
        System.out.print("\nEnter the phrase that will be encrypted: ");
        String message = in.nextLine();
        String newMessage = encrypt(message);
        System.out.println("Here is the encrypted message using the cipher alphabet: ");
        PrintWriter outM = new PrintWriter("cipherMessage.txt");
        System.out.println(newMessage + "\n");
        outM.println(newMessage);
        outM.close();
    }
   
    public static void createNewAlphabet()
    {
        int number;
        while(alphabet.size() > newAlphabet.size())
        {
            number = (int)(Math.random() * 26);
            if(newAlphabet.contains(alphabet.get(number)))
            {    
                newAlphabet.remove(alphabet.get(number));
            }
            else 
            {
                newAlphabet.add(alphabet.get(number));
            }
        }
    }
   
    public static void displayNewAlphabet(ArrayList<Character> newAlphabet) throws IOException
    {
        PrintWriter outA = new PrintWriter("cipherAlphabet.txt");
        for (int loop = 0; loop < 26; loop++)
        {
            System.out.print(newAlphabet.get(loop));
            
            outA.println(newAlphabet.get(loop));
        }
        outA.close();
    }
  
    public static String encrypt(String message)
    {
        String upper = message.toUpperCase();
        String newMessage = "";
        char newLetter;
        char letter;
        int letterPosition;
        //Runs through the message and encrypts it
        for (int loop = 0; loop < message.length(); loop++)
        {
            if(upper.charAt(loop) >= 65 && upper.charAt(loop) <= 90)
            {
                letterPosition = alphabet.indexOf(upper.charAt(loop));
                newMessage += newAlphabet.get(letterPosition);
            }
            else
            {
                newMessage += upper.charAt(loop);
            }
        }     
        return newMessage;
    }
} 

/**
 * This class is used to decrypt messages with a Caesar shift number.
 * 
 * @author Christopher Goad
 * @version 3-13-12
 */

import java.io.File;
import java.util.Scanner;
import java.util.ArrayList;
import java.io.IOException;
import java.io.PrintWriter;
public class ChrisGoadDecipher
{
    private static ArrayList<Character> cipherAlphabet = new ArrayList<Character>();
    private static ArrayList<Character> alphabet = ChrisGoadCipherTester.alphabet;
    
    public ChrisGoadDecipher()
    {   
        
    }
   
    public static void getInput() throws IOException
    {
        createcipherAlphabet();
        System.out.println("Here is the alphabet being used for decryption:");
        displayNewAlphabet(cipherAlphabet);
        String message = message();
        String newMessage = decrypt(message);
        System.out.println("Here is the decrypted message using the cipher alphabet: ");
        System.out.println(newMessage + "\n");
    }
    
    public static String message() throws IOException
    {
        File file = new File("cipherMessage.txt");
        Scanner in = new Scanner(file);
        String message = "";
        while(in.hasNext())
        {
            message = in.nextLine();
        }
        return message;
    }
    
    public static void displayNewAlphabet(ArrayList<Character> newAlphabet)
    {
        for (int loop = 0; loop < 26; loop++)
        {
            System.out.print(cipherAlphabet.get(loop));
        }
    }
    
    public static void createcipherAlphabet() throws IOException
    {
        File file = new File("cipherAlphabet.txt");
        Scanner in = new Scanner(file);
        while(in.hasNext())
            {
                String character = in.next();
                int num = alphabet.indexOf(character);
                cipherAlphabet.add(alphabet.get(num));
            }
        }
        
    public static String decrypt(String message)
    {
        String upper = message.toUpperCase();
        String newMessage = "";
        char newLetter;
        char letter;
        int letterPosition;
        //Runs through the message and encrypts it
        for (int loop = 0; loop < message.length(); loop++)
        {
            if(upper.charAt(loop) >= 65 && upper.charAt(loop) <= 90)
            {
                letterPosition = alphabet.indexOf(upper.charAt(loop));
                newMessage += cipherAlphabet.get(letterPosition);
            }
            else
            {
                newMessage += upper.charAt(loop);
            }
        }     
        return newMessage;
    }
}

[Anayonkar Shivalkar]

Hi Christopher,

Welcome to CodeRanch!

I could not find the attached project folder and assignment instructions.

Besides, at CodeRanch, we strongly encourage users to learn on their own, instead of providing ready-made solutions. Needless to say, you can ask/discuss any doubt you are facing during your assignments and we'll help you in finding the solution (instead of giving you the solution )

Also, please be specific about the problem. You've only provided a small mention of problem (in subject line) - you are facing out of bounds exception. Can you please be more specific about it (e.g. providing call stack etc)?

From initial look, I can see that in your ChrisGoadDecipher class, you are looping over cipherAlphabet for 26 times. What if cipherAlphabet's size is less than 26?

I hope this will help.

[Christopher Goad]

I'm sorry I implied I wanted the answers. That is not what I meant.
Anyway, I know the problem is in my decryption class. The error always occurs when reading back the cipher alphabet from the txt file. Could you compile my code and take a look for yourself?

[Winston Gutkowski]

Christopher Goad wrote:Anyway, I know the problem is in my decryption class. The error always occurs when reading back the cipher alphabet from the txt file.

Actually, I suspect that's not the case. The problem looks to be in your createNewAlphabet() method, which I'm still not quite sure what it's doing, but it doesn't appear to use a Caesar shift.

Assuming that you simply want to use a random combo of the original letters to encrypt a message (and if you want your encryption to allow blanks, it should probably have 27, not 26 - and 53 if you want to allow mixed case), consider using Collections.shuffle(); and if you want your decrypt() function to work nice and fast, I'd suggest that you put the result of that shuffle into a HashMap (specifically, a HashMap<Character, Integer>).

If you truly want to use a Caesar shift, then your new "alphabet" MUST be a rotation of the original - so have a look at the 'mod' (%) operator.

HIH

Winston

[Christopher Goad]

That's what I meant. Anyway in my createNewAlphabet() method i am trying to read to read the random alpabet i made in the txt file and then assign it to the cipherAlphabet array.

[Winston Gutkowski]

Christopher Goad wrote:That's what I meant.

Erm...what's what you meant?

Anyway in my createNewAlphabet() method i am trying to read to read the random alpabet i made in the txt file and then assign it to the cipherAlphabet array.

So, do you:
(a) Know whether you read it back in correctly.
(b) Know whether your method is translating it back correctly?
And the easiest way to track that is with debug statements (or, indeed, a debugger)...

The fact is that, to decrypt, the ONLY thing you should need is your jumbled "alphabet".

Winston

[Christopher Goad]

I meant the problem was in the ChrisGoadDecipher class but more specificly in the createNewAlphabet() method. I do not. Could you help me figure the problem out because I am not sure what is going on.

[Christopher Goad]

I figured out the problem in my createnewalphabet() method. I didnt have it changed to a char.

Now I have one last problem. I need to reverse the cipher in my decrypt method. How could this be done?

/**
 * This class is used to decrypt messages with a Caesar shift number.
 * 
 * @author Christopher Goad
 * @version 3-13-12
 */

import java.io.File;
import java.util.Scanner;
import java.util.ArrayList;
import java.io.IOException;
import java.io.PrintWriter;
public class ChrisGoadDecipher
{
    private static ArrayList<Character> cipherAlphabet = new ArrayList<Character>();
    private static ArrayList<Character> alphabet = ChrisGoadCipherTester.alphabet;
    
    public ChrisGoadDecipher()
    {   
        
    }
   
    public static void getInput() throws IOException
    {
        createcipherAlphabet();
        System.out.println("Here is the alphabet being used for decryption:");
        displayNewAlphabet(cipherAlphabet);
        String message = message();
        String newMessage = decrypt(message);
        System.out.println("Here is the decrypted message using the cipher alphabet: ");
        System.out.println(newMessage + "\n");
    }
    
    public static String message() throws IOException
    {
        File file = new File("cipherMessage.txt");
        Scanner in = new Scanner(file);
        String message = "";
        while(in.hasNext())
        {
            message = in.nextLine();
        }
        return message;
    }
    
    public static void displayNewAlphabet(ArrayList<Character> newAlphabet)
    {
        for (int loop = 0; loop < 26; loop++)
        {
            System.out.print(cipherAlphabet.get(loop));
        }
    }
    
    public static void createcipherAlphabet() throws IOException
    {
        File file = new File("cipherAlphabet.txt");
        Scanner in = new Scanner(file);
        while(in.hasNext())
            {
                String character = in.next();
                char c = character.charAt(0);
                int num = (alphabet.indexOf(c));
                cipherAlphabet.add(alphabet.get(num));
            }
        }
        
    public static String decrypt(String message)
    {
        String upper = message.toUpperCase();
        String newMessage = "";
        char newLetter;
        char letter;
        int letterPosition;
        //Runs through the message and decrypts it
        for (int loop = 0; loop < message.length(); loop++)
        {
            if(upper.charAt(loop) >= 65 && upper.charAt(loop) <= 90)
            {
                letterPosition = alphabet.indexOf(upper.charAt(loop));
                letterPosition = letterPosition;
                newMessage += cipherAlphabet.get(letterPosition); 
            }
            else
            {
                newMessage += upper.charAt(loop);
            }
        }     
        return newMessage;
    }
}

[Christopher Goad]

Ahah, I got it. All I had to do was flip the cipherAlphabet and Alphabet!

It works perfect now!

public static String decrypt(String message)
    {
        String upper = message.toUpperCase();
        String newMessage = "";
        char newLetter;
        char letter;
        int letterPosition;
        //Runs through the message and decrypts it
        for (int loop = 0; loop < message.length(); loop++)
        {
            if(upper.charAt(loop) >= 65 && upper.charAt(loop) <= 90)
            {
                letterPosition = cipherAlphabet.indexOf(upper.charAt(loop));
                letterPosition = letterPosition;
                newMessage += alphabet.get(letterPosition); 
            }
            else
            {
                newMessage += upper.charAt(loop);
            }
        }     
        return newMessage;
    }

One last problem.

Whenever I enter yes to tryAgain it does nothing

/**
* This class tests CaesarShiftEncryption and CaesarShiftDecryption classes
*
* @author Christopher Goad
* @version 3-13-12
*/

import java.io.File;
import java.util.Scanner;
import java.util.ArrayList;
import java.io.IOException;
import java.io.PrintWriter;
public class ChrisGoadCipherTester
{
    //constant for the alphabet
    public static ArrayList<Character> alphabet = makeAlphabet();
   
    public ChrisGoadCipherTester()
    {
    }
   
    public static ArrayList<Character> makeAlphabet()
    {
        ArrayList<Character> alphabet = new ArrayList<Character>();
        int letter = 65;
        for (int loop = 0; loop < 26; loop++)
        {
            alphabet.add((char)letter);
            letter++;
        }
        return alphabet;
    }
    
    public static void main(String[] args) throws IOException
    {
    	String tryAgain = "yes";
        if(tryAgain.equalsIgnoreCase("yes"))
       {
        Scanner in = new Scanner(System.in);
        //Menu for the user
        System.out.println("===============================");
        System.out.println("     [A] Chris Goad Cipher ");
        System.out.println("     [B] Chris Goad Decipher ");
        System.out.println("           [Q] Quit           ");
        System.out.println("===============================");
        System.out.print("Please select an letter option from the above menu and hit enter: ");
       
        String input = in.next();
        if (input.equalsIgnoreCase("A"))
        {
            ChrisGoadCipher.getInput();
            System.out.println("Enter yes to try again.");
            tryAgain = in.next();
        }
        else if (input.equalsIgnoreCase("B"))
        {
            ChrisGoadDecipher.getInput();
            System.out.println("Enter yes to try again.");
            tryAgain = in.next();
        }
        else if (input.equalsIgnoreCase("Q"))
        {
            System.out.println("You chose to quit. Goodbye!");
        }
        else
        {
            System.out.println("You did not choose a vaild option.");
            System.out.println("Enter yes to try again.");
            tryAgain = in.next();
        }
       }
       else 
       {
        System.out.println("Goodbye!");
       }
    }
}

[Winston Gutkowski]

Christopher Goad wrote:One last problem.
Whenever I enter yes to tryAgain it does nothing

You know what? Compared to what you've just solved that's a fart in a storm; so I'm going to leave it up to you.

Two tips (and I say this without even having looked at your code):
1. AvoidTheEqualityOperator (←click).
2. Add debug code, and TEST.

There are some things you just can't get around.

Winston

[Christopher Goad]

Okay, I understand. Can't believe I got that by myself(With some small hints). Thanks for the help.

I'll be back lol

[Winston Gutkowski]

Christopher Goad wrote:Okay, I understand. Can't believe I got that by myself(With some small hints). Thanks for the help.

Glad to help - and isn't it much better when you DO get it yourself?

Winston