Unusual behavior of Simple Cipher Program

[Vasiq Molvizadah]

  package ceasarcipher;

import java.io.BufferedReader;
import java.io.InputStreamReader;


/**
 *
 * @author Vasiq Mz
 */
public class Cipher {
    public static void main(String[] args)
    {
        String userInput=null;
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        try
        {
            System.out.println("Enter the text you want to cipher.");
            userInput = br.readLine();
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }
        
        char[] alphabets = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
                           'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
                           'u', 'v', 'w', 'x', 'y', 'z'};

        int randomValue = (int) (Math.random() * 10);        

        char[] cipherText = new char[userInput.length()];

        int position=0;

        //A loop to fill the cipher text.
        for(int i=0; i<userInput.length(); i++)
        {
            // A labeled loop to find the correct position of the alphabet
            // and shift it according to the random value.
            alphabetChecker:
                for(int j=0; j><alphabets.length; j++)
                {
                    if(alphabets[j] == userInput.charAt(i))
                    {
                     position = j;                                          
                     break alphabetChecker;
                    }
                }                
             int shift = position + randomValue;

             // If the shift value is greater than 26 then do some addition.
             if(shift >= alphabets.length)
             {
              shift = 0 + randomValue;
             }
             else
             {
             cipherText[i] = alphabets[shift];
             }
        }


        System.out.print("The cipher text is ");
        //Loop for printing the cipher text.
        for(int k=0; k<cipherText.length; k++)
        {            
            System.out.print(cipherText[k]);            
        }
        System.out.println();        
    }
}  

If I give the input as "vasiqmz" or a word such as "x","y" then the output which I'm getting is kinda confusing....

[Vasiq Molvizadah]

Output :
Enter the text you want to cipher.
vasiqmz
The cipher text is zewmuq(And a box symbol appears which i'm not able to print it here)

I know the reason is because of the else loop but one thing i'm not getting is..if there is no char at a given position then it should display it's value as null instead of a symbol which in case here is a box.

Any reason for that ???

Thanks for reading it....
Any comments on the program....

[David Newton]

What gets stored in the coded string when shift >= alphabets.length?

[David Newton]

Also note that it's possible the text won't be encoded at all.

[Vasiq Molvizadah]

David Newton wrote:What gets stored in the coded string when shift >= alphabets.length?

If the IF loop is correct then nothing gets stored in that position...If nothing gets stored then that position should contain a "null" value instead of any symbol..I mean after all the default value of char is null....

[David Newton]

And what would a null character print out as?

[Vasiq Molvizadah]

David Newton wrote:And what would a null character print out as?

Ok i get it now....if there is nothing in that position then it'll store "'\u0000'" or "0" which is basically a null value and a null value is printed out as a box symbol....

Thanks a lot for reading the program and helping me out with the problem....David.

[David Newton]

No problem--glad to help :)