Question

Change the following Shift Cipher program so that it uses OOP(constructor, ect.)

import java.util.*;

import java.lang.*;

/**

*

* @author STEP

*/

public class ShiftCipher

{

/**

* @param args the command line arguments

*/

public static void main(String[] args) {

// TODO code application logic here

Scanner input = new Scanner(System.in);

String plainText;

System.out.print("Please enter your string: "); // get message

plainText = input.nextLine();

System.out.print("Please enter your shift cipher key: "); // get s

int s = input.nextInt();

int length = plainText.length(); // get length of msg

int[] cipherText = new int[length];

for (int i=0;i<length;i++) {

cipherText[i] = (int)plainText.charAt(i); //convert string to ascii

}

int[] encryption = cipherText.clone();

for(int i=0;i<length;i++) {

encryption[i] = (encryption[i] + s) % 127;//Encrypt message

}

String encryptedText = "";

for(int i=0;i<length;i++) {

encryptedText += (char)(encryption[i]); //initialize encryption string

}

String decryptedText = encryptedText; //decrypt message

for (int i=0;i<length;i++) {

cipherText[i] = 127 + (((int)(decryptedText.charAt(i))-s) % 127);//decrypt into cipher string

}

System.out.println("Decrypted message: " + plainText); //output results

System.out.println("Shift : " + s);

System.out.println("Encrypted message: " + encryptedText); //

System.out.print("Decrypted message: ");

for(int i=0;i<length;i++) {

System.out.print((char)cipherText[i]);

}

System.out.print("\n");

}

}

Answer 1

public class ShiftCipher {
  
   //class member which is key of encryption
   private int s;
  
   //constructor
   public ShiftCipher(int s)
   {
       this.s = s;
   }
   //getter methof
   public int getS() {
       return s;
   }
  
   //this method will encrypt argument passed with the key s
   public String encrypt(String plainText)
   {
       int length = plainText.length(); // get length of msg
       int[] cipherText = new int[length];
       for (int i=0;i<length;i++) {
           cipherText[i] = (int)plainText.charAt(i)
                   ; //convert string to ascii
       }

       int[] encryption = cipherText.clone();
       for(int i=0;i<length;i++) {
           encryption[i] = (encryption[i] + s) % 127;//Encrypt message
       }

       String encryptedText = "";
       for(int i=0;i<length;i++) {
           encryptedText += (char)(encryption[i]); //initialize encryption string
       }
      
       return encryptedText;
   }
  
   //this method will be used to decrypt the encrypted text
   public String decrypt(String encryptedText)
   {
       int length = encryptedText.length();
       int[] cipherText = new int[length];
       for (int i=0;i<length;i++) {
          
           cipherText[i] = ((127 + (int)(encryptedText.charAt(i))-s) % 127);
           //decrypt into cipher string
       }
       String decryptedText = "";
       for(int i=0;i<length;i++) {
           decryptedText += (char)(cipherText[i]); //initialize encryption string
       }
      
       return decryptedText;
   }
}

public class ShiftCipherTest {

   public static void main(String[] args) {
       // TODO Auto-generated method stub
       Scanner input = new Scanner(System.in);
       String plainText;
       System.out.print("Please enter your string: "); // get message
       plainText = input.nextLine();
       System.out.print("Please enter your shift cipher key: "); // get s
       int s = input.nextInt();
       ShiftCipher sc = new ShiftCipher(s);
      
       String encryptedText = sc.encrypt(plainText);
       String decryptedText = sc.decrypt(encryptedText);
      
       System.out.println("\n\nPlain Text: " + plainText);
      
       System.out.println("Shift : " + s);

       System.out.println("Encrypted message: " + encryptedText); //

       System.out.print("Decrypted message: " + decryptedText);

   }

}

If there is anything that you do not understand, or need more help then please mention it in the comments section.