Question

Question 1 :

Create an interface MessageDecoder that has a single abstract method decode( cipherText), where cipherText is the message to be decoded. The method will return the decoded message. Create a class SubstitutionCipher that implements the interface MessageDecoder as described above. The constructor should have one parameter called shift. Define the method decode so that each letter is shifted by the value in shift. For example, if shift is 3, a will be replaced by d, b will be replaced by e, c will be replaced by f, and so on. Hint: You may wish to define a private method that shifts a single character. Create a class ShuffleCipher that implements the interface MessageDecoder. The constructor should have one parameter called n. Define the method decode so that the message is shuffled n times. To perform one shuffle, split the message in half and then take characters from each half alternately. For example, if the message is “abcdefghi”, the halves are “abcde” and “fghi”. The shuffled message is “afbgchdie”. Hint: You may wish to define a private method that performs one shuffle. Finally, write a program that allows a user to encode and decode messages entered on the keyboard

Question 2

Create a JavaFX application that uses a TextField to get a message and encode or decode it using the classes described in Question 1. Use four buttons to control the kind of cipher used and to specify whether to encode or decode the message. Also, use a TextField to get the number used in the constructor for the ciphers.

Answer 1

MessageDecoder.java

public interface MessageDecoder {

   public String decode(String cipherText);
}

ShuffleCipher.java

public class ShuffleCipher implements MessageDecoder{
  
private int num;
  
   public ShuffleCipher(int number) {
      
       this.num = number;
   }

   @Override
   public String decode(String text) {
      
       int size = text.length();
       String text1;
       String text2;
      
       if(size%2==0) {
          
       while(num>0) {
      
           text1=text.substring(0, size/2);
           text2=text.substring(size/2,size);
           text ="";
           for(int i=0; i<text2.length();i++) {
               text = (text + text1.charAt(i))+ text2.charAt(i);
           }
          
       num--;  
       }
      
       }
      
       else {
          
           while(num>0) {
               text1=text.substring(0, size/2+1);
               text2=text.substring(size/2+1 ,size);
              
               text ="";
               for(int i=0; i<text2.length();i++) {
                   text = (text + text1.charAt(i))+ text2.charAt(i);
               }
              
               text = text + text1.charAt(size/2);
              
               num--;  
               }
          
       }
          
       return text;
   }

}

SubstitutionCipher.java

public class SubstitutionCipher implements MessageDecoder{
  
   private int num;
  
   public SubstitutionCipher(int number) {
      
       this.num = number;
   }

   @Override
   public String decode(String text) {
      
      
       char[] array = text.toCharArray();
      
       int size = text.length();
      
       String ans = "";
      
       for(int i=0; i<size; i++) {
          
           array[i] = (char) (array[i] + num);
          
           ans = ans + array[i];
          
       }
      
       return ans;
   }

}

MainMethod .java

public class MainMethod {

   public static void main(String[] args) {
  
      
       Scanner sc = new Scanner(System.in);
      
       //Testing SubstitutionCipher
      
       System.out.println("Testing Substitution Cipher ");
       System.out.println("Enter the shift value. It should be integer");
      
       int shiftValue = sc.nextInt();
      
       MessageDecoder md = new SubstitutionCipher(shiftValue);
      
       System.out.println("Enter the input to decode. It should be the string of alphabets");

       String input = sc.next();
      
       System.out.println("Decoded Message is " + md.decode(input));
      
       //Testing ShuffleCipher
      
       System.out.println("********Testing SuffleCipher*************");
      
System.out.println("Enter the shift value. It should be integer");
      
   shiftValue = sc.nextInt();
      
       md = new ShuffleCipher(shiftValue);
      
       System.out.println("****************Testing Decoding***************************");
      
       System.out.println("Enter the input to decode. It should be the string of alphabets");

       input = sc.next();
      
       System.out.println("Decoded Message is " + md.decode(input));
      
      
      
      
   }

}

Output is

Testing Substitution Cipher
Enter the shift value. It should be integer
2
Enter the input to decode. It should be the string of alphabets
abcd
Decoded Message is cdef
********Testing SuffleCipher*************
Enter the shift value. It should be integer
3
****************Testing Decoding***************************
Enter the input to decode. It should be the string of alphabets
john
Decoded Message is jhon

If you left with any doubts. feel free to ask.