Question

create a Java class ShiftCipher

The program ShiftCipher should take two inputs from the terminal. The first should be a string of any length which contains any type of symbol (the plaintext). The second will be a shift value which should be between 0 and 25 inclusive (though you may design your program to be resilient to shifts beyond this value). The program should print the cipher text, in which each of the alphabetic characters in the string is shifted by the given amount, for example:

Input	Shift Value	Result
A	0	A
A	1	B
A	5	F
Z	1	A

Lower case letters should be shifted in the same manner (meaning that a lower case letter should remain lower case, and an upper case should remain upper case). All other characters (i.e. those that are not alphabetic) should remain unchanged. Print the resulting shifted string to the terminal.

For example, given the input:

Iacta alea est!
3

the program should print the output:

Ldfwd dohd hvw!

Hint - You may want to consider the relationship between strings, arrays and ASCII values.

Extension - Abstract your core shifting algorithm into a method/function which can accept positive or negative shift values. Now write a decode method which given a cipher text and a known shift value returns the string to its original form. Validate the relationship between your methods by ensuring that applying first the encode function and then the decode function (with the same shift) returns the original plaintext.

Answer 1

import jdk.swing.interop.SwingInterOpUtils;

class Main {
    public static String shift(String s, int shift) {
        //Variable to store ans
        String ans = "";
        //Loop through all chars in the string
        for (int i = 0; i < s.length(); i++) {
            //Current character
            char ch = s.charAt(i);
            //Modified new character
            int newchar = ch;
            //Check if char is lowercase or uppercase
            if (Character.isLowerCase(ch)) {
                //Shift the letter
                newchar = (int) ch + shift;
                //If char exceeds 'z' or 'a', then wrap it
                if (newchar > 'z') {
                    newchar = 'a' + (newchar - 'z' - 1)%26;
                } else if (newchar < 'a') {
                    newchar = 'z' - ('a' - newchar + 1)%26;
                }
            }
            else if(Character.isUpperCase(ch)){
                newchar = (int) ch + shift;
                if (newchar > 'Z') {
                    newchar = 'A' + (newchar - 'A' - 1)%26;
                } else if (newchar < 'A') {
                    newchar = 'Z' - ('A' - newchar + 1)%26;
                }
            }
            ans = ans + (char)newchar;
        }
        return ans;
    }


    public static void main(String[] args) {
        String s = "lacta alea est!";
        System.out.println("Original : "+s);
        String encrypted = shift(s,3);
        System.out.println("Encrypted : "+encrypted);
        String decrypted = shift(encrypted,-3);
        System.out.println("Decrypted : "+decrypted);
        System.out.println("Decrypted and original match? "+(decrypted.equals(s)));
    }
}

OUTPUT :

IVIU Run: Main X "C:\Program Files\Java\jdk-13\bin\java.exe" "-javaagent: Original : lacta alea est! Encrypted : odfwd dohd hvw! Decrypted : lacta alea est! Decrypted and original match? true . Process finished with exit code 0