Write a program to calculate implement Monoalphabetic cipher encryption - decryption.

 

Code:

import java.util.Scanner;


public class MonoalphabeticCipher {

    public static void main(String[] args) {

        char []real={'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'};
        char []mono={'q','w','e','r','t','y','u','i','o','p','a','s','d','f','g','h','j','k','l','z','x','c','v','b','n','m'};

        Scanner sc = new Scanner(System.in);
        String str;
        int len;

        System.out.print("1. Encryption 2. Decryption: ");
        int choice = sc.nextInt();
        switch (choice) {
            case 1:
                System.out.print("Enter plain text:");
                str = sc.next();

                len = str.length();
                char []ci = new char[len];

                for(int i=0;i<len;i++){
                    for(int j=0;j<26;j++){
                        if(real[j]==str.charAt(i)){
                            ci[i]=mono[j];
                            break;

                        }

                    }

                }
                System.out.print("Encrypted Text is:");
                for(int i=0;i<len;i++){
                    System.out.print(ci[i]);

                }
                break;
            case 2:
                System.out.print("Enter Encrypted text:");
                str = sc.next();

                len = str.length();
                char []di=new char[len];

                for(int i=0;i<len;i++){
                    for(int j=0;j<26;j++){
                        if(mono[j]==str.charAt(i)){
                            di[i]=real[j];
                            break;
                        }

                    }

                }

                System.out.print("Decrypted Text is:");

                for(int i=0;i<len;i++){
                    System.out.print(di[i]);

                }
                break;
            default:
                break;
        }

    }

}

Output: