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;

    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();
                    break;
                case 'Q':
                    quit();
                    break;
                default:
                    System.out.println("Not a valid answer :(");
            }

        }
    }

    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 generated*");
    }
    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: ");
        for(char x : letters){
            System.out.print(x);
        }

        System.out.println();
    }

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

        letters = message.toCharArray();

        for(int i=0;i<letters.length;i++){

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

        System.out.println();
    }

    private void quit(){
        System.out.println("Good bye :)");
        System.exit(0);
    }

}