Question

1. Modify the Encryption program so that it uses the following encryption algorithm:

   • Every letter (both uppercase and lowercase) converted to its successor except z and Z, which are converted to 'a' and 'A' respectively (i.e., a to b, b to c, …, y to z, z to a, A to B, B to C, …, Y to Z, Z to A)

   • Every digit converted to its predecessor except 0, which is converted to 9 (i.e., 9 to 8, 8 to 7, … 1 to 0, 0 to 9)

   • Everything else unchanged.

Hand in:

Encryption.java

Note:

You must modify the specifications (API) of the methods involved as well.  

Answer 1

Thanks for the question, It would have good if you have shared the previous code that needed to be modified, nevertheless, I have written the method that takes in a plain text and encrypt into based on the logic asked in the quesiton.

Here is the code.

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import java.util.Scanner;

public class Encryption {

    /**
     *  Main logic of encryption
     * @param plainText : The text we want to encrypt
     * @return : The encrypted text using the given logic
     */
    public static String encrypt(String plainText) {

        String encrypted = "";
        for (int i = 0; i < plainText.length(); i++) {

            char letter = plainText.charAt(i);
            // logic to handle lowercase letters
            if (Character.isLowerCase(letter)) {
                letter = (char) (letter + 1);
                if (Character.isLowerCase(letter)) {
                    encrypted += String.valueOf(letter);
                } else {
                    encrypted += String.valueOf('a');
                }
            }
            // logic to handle uppercase letters
            else if (Character.isUpperCase(letter)) {
                letter = (char) (letter + 1);
                if (Character.isUpperCase(letter)) {
                    encrypted += String.valueOf(letter);
                } else {
                    encrypted += String.valueOf('A');
                }
            } 
            // logic to handle digits character
            else if (Character.isDigit(letter)) {
                letter = (char) (letter - 1);
                if (Character.isDigit(letter)) {
                    encrypted += String.valueOf(letter);
                } else {
                    encrypted += String.valueOf('9');
                }
            }
            // logic to handle characters which are not alpha numeric
            else {
                encrypted += String.valueOf(letter);
            }
        }
        return encrypted; // returns the encrypted stirng
    }

    public static void main(String[] args) {


        Scanner scanner = new Scanner(System.in);
           // ask user to enter a text to encrypt
        System.out.print("Enter text you like to encrypt: ");
        String plainText = scanner.nextLine();
             // display the encrypted string
        System.out.println("Encrypted String: "+ encrypt(plainText));

    }
}

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