EncryptionProgram.java

import java.util.*;

public class EncryptionProgram {

    private Scanner scanner;
    private Random random;
    private ArrayList<Character> list;
    private ArrayList<Character> shuffledList;
    private char character;
    private String line;
    private char[] letters;
    private char[] secreteLetters;

    EncryptionProgram(){
         scanner = new Scanner(System.in);
         random = new Random();
         list = new ArrayList<>();
         shuffledList = new ArrayList<>();
         character = ' ';

         newKey();
         askQuestion();

    }
    private void askQuestion(){
        while(true){
            System.out.println("*******************************************************");
            System.out.println("What do you want to do? ");
            System.out.println("(N)ewKey, (G)etKey, (E)ncrypt, (D)ecrypt, (Q)uit");
            char response = Character.toUpperCase(scanner.nextLine().charAt(0));

            switch(response){
                case 'N':
                    newKey();
                    break;
                case 'G':
                    getKey();
                    break;
                case 'E':
                    encrypt();
                    break;
                case 'D':
                    decrypt(secreteLetters);
                    break;
                case 'Q':
                    quit();
                    break;
                default:
                    System.out.println("Invalid choice ");

            }
        }

    }
    private void newKey(){

        character = ' ';
        list.clear();
        shuffledList.clear();

        for(int i = 32; i<127; i++ ){
            list.add(Character.valueOf(character));
            character++;
        }
        shuffledList = new ArrayList<>(list);
        Collections.shuffle(shuffledList);
        System.out.println("A new key has been created");

    }

    private void getKey(){
        System.out.println("Key: ");
        for(Character x : list){
            System.out.print(x);
        }
        System.out.println();
        for(Character x : shuffledList){
            System.out.print(x);
        }
        System.out.println();

    }
    private void encrypt(){
        System.out.println("Enter a message to be encrypted: ");
        String message = scanner.nextLine();

        letters = message.toCharArray();

        for(int i = 0; i<letters.length; i++){
                for(int j = 0; j<list.size(); j++){
                    if(letters[i]==list.get(j)){
                        letters[i]=shuffledList.get(j);
                        break;
                    }
                }
        }
        System.out.println("Encrypted message: ");
        for(char x : letters){
            System.out.print(x);
        }
        secreteLetters = letters;
        System.out.println();
    }
    private void decrypt(char[] secreteLetters){

        for(int i = 0; i<secreteLetters.length; i++){
            for(int j = 0; j<shuffledList.size(); j++){
                if(secreteLetters[i]==shuffledList.get(j)){
                    secreteLetters[i]=list.get(j);
                    break;
                }
            }
        }
        System.out.println("Decrypted message: ");
        for(char x : secreteLetters){
            System.out.print(x);
        }
        System.out.println();

    }
    private void quit(){
        System.out.println("Thank you, have a nice day bro. Bye!");
        System.exit(0);
    }

}