Unit 4 Team Homework

Caesar Cipher Program

Try to write a caesar cipher program that shifts each letter in a message 3 letters forward. Use any of the methods you learned today. Use it to decode the 3 messages we've given you!

public class CaesarCipher {

    public static void main(String[] args) {

        String[] letters = {"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"};
        String message1 = "Kfzb gly!";
        String message2 = "zlab zlab zlab";
        String message3 = "prmbozxifcoxdfifpqfzbumfxifalzflrp";

        int shiftBy = 3 ; // showing how much to shift by

        CaesarCipher caesarCipher = new CaesarCipher(); // instantiating CaesarCipher class

        System.out.println("Decrypted Message1 : " + caesarCipher.decryptMessage(message1, shiftBy));
        System.out.println("Decrypted Message2 : " + caesarCipher.decryptMessage(message2, shiftBy));
        System.out.println("Decrypted Message3 : " + caesarCipher.decryptMessage(message3, shiftBy));
    }

    // method for decrypting given message by the shift int value 
    String decryptMessage(String input, int shiftBy){ 

        int asciia =(int) 'a'; // assigning ascii values for a 

        String decryptMessage = "";
        for(int i=0 ; i < input.length(); i++){
                char c = input.charAt(i) ; 
                char newChar = c ;
                // does decryption only for letters (not the exclamation mark, not spaces, etc.)
                if( Character.isLetter(c) ){
                    int intValue = (int) c ; // finds the ascii value for given letter
                    int newValue = (intValue - asciia + shiftBy ) % 26 ; // assiging deciphered ascii value by subtracting the ascii value and adding the shift value
                    newValue = newValue + asciia ;
                    newChar = (char) newValue; // converting ascii value to new character
                }
                decryptMessage += newChar ;
        }
        return decryptMessage;
    }

}
CaesarCipher.main(null);

Decrypted Message1 : Nice job!
Decrypted Message2 : code code code
Decrypted Message3 : supercalifragilisticexpialidocious