please fix my code this is about encryption

I am tasked with writing a program the will generate a random alphabet. The user is then prompted to enter a plaintext message. The program must then perform a substitution cipher to generate an encrypted message using your random cipher alphabet. When I enter a message, the encrypted message that is returned is "null". I'm not sure what is wrong with my code.

import java.util.Scanner;    public class noob2  {      public  noob2(String message)      {      }        private static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";      private String myNewAlphabet;      private String myEncryptedMessage;        public String generateRandomAlphabet()      {          int random;          String myNewAlphabet = "";            char[] alphabet = { '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' };            for (int i=0; i <26; i++) {              // keep generating random index until an unused alphabet is found              do {                  random = (int)(Math.random() * 26);              } while (myNewAlphabet.indexOf(alphabet[random]) >= 0);                myNewAlphabet += alphabet[random];          }            //temporary code just to display original an new random alphabet          System.out.print("   Alphabet: ");          for (int x =0; x <26; x++)          {              System.out.print(alphabet[x]);          }            System.out.println();          System.out.println("Cipher Alphabet: " + myNewAlphabet);          // this section will be deleted          return myNewAlphabet;      }        public String substitutionCipher(String message)      {          String encryptedMessage = "";            for(int i = 0; i < message.length(); i++)          {              int positionOfCharacterInMessage = ALPHABET.indexOf(message.charAt(i));    // this accounts for spaces or other symbols that may be in the message to be encrypted                if (positionOfCharacterInMessage == -1)              {                  encryptedMessage += message.charAt(i);                  continue;              }                encryptedMessage += myNewAlphabet.charAt(positionOfCharacterInMessage);            }            return myEncryptedMessage;      }        //getter method to return Encrypted message      public String getEncryptedMessage()      {          return myEncryptedMessage;      }  }    //*************************************************************  import java.util.Scanner;    public class RandomCipherTester {      public static void main(String[] args) {          Scanner in = new Scanner(System.in);          System.out.println("Enter a plaintext message for processing");          Scanner sc = new Scanner(System.in);          String plaintext = sc.nextLine();          noob2 x = new noob2(plaintext);          x.generateRandomAlphabet();          System.out.println("The encrypted message is " + x.getEncryptedMessage());      }  }  

https://stackoverflow.com/questions/66594289/please-fix-my-code-this-is-about-encryption March 12, 2021 at 12:41PM