Question

Cipher

Program Specifications: You are to write a program called, "Cipher123" that reads in an encoded message using the 1-2-3 cipher and returns the decoded message. The program should continue prompting for additional encoded messages until the user chooses to quit the program.

When decoding a message, we take the first letter of the first word, the second letter of the second word and the third letter of the third word and concatenate them. We repeat this same process 1-2-3 until there are no more words in the phrase. Suppose we received the message "Randy's lucky penny" that we know is encrypted using 1-2-3 encryption. We would take the first character from the first word ( 'R' ) and concatenate it with the second character of the second word ( 'u' ) and concatenate that with the third character of the third word ( 'n' ). Put it all together and we know that someone is telling us to “Run”.

Program Decomposition:

1. public static String getUserInput(Scanner scnr) This method accepts a scanner parameter, prompts the user for the encoded message and returns the encoded message to the user. The user may enter the message on multiple lines and signals that they have finished entering the message by hitting the enter key on a line by itself. Data validation: The user must not enter an empty string as the decoded message. See sample run above.
2. public static String decodeMessage(Scanner wordScanner) This method accepts a scanner parameter that is pointing to the encoded message. The method processes the string word by word using the 123 Cipher method and returns the deciphered string for printing. If while decoding, you come across a word that is smaller than the character needed (e.g., you need character 3 and the word is "go", you should print an appropriate message and stop decoding.
3. Add more methods as needed

Sample Run

Enter the encoded message on one or several lines. Enter an empty line when you are finished typing your message:

Randy's lucky penny

<-- user hits carriage return to signal message is complete

You entered: Randy's lucky penny

The decoded message is: Run

Again? (Y/N)? y

Enter the encoded message on one or several lines. Enter an empty line when you are finished typing your message:

Randy's

lucky

penny

<-- user hits carriage return to signal message is complete

You entered: Randy's

lucky

penny

The decoded message is: Run

Again? (Y/N)? y

Enter the encoded message on one or several lines. Enter an empty line when you are finished typing your message:

<-- user hits carriage return for the message which is an invalid message

Please enter a message.

Funny Al's aly

<-- user hits carriage return to signal message is complete

You entered: Funny Al's aly

The decoded message is: Fly

Again? (Y/N)? n

If user enters a bad message (here the second word needs to have two letters - end the program and display “Sorry - this message cannot be decoded using 123 Cipher. Again? (Y/N)?"

Enter the encoded message on one or several lines. Enter an empty line when you are finished typing your message:

What a crazy message

<-- user hits carriage return to signal message is complete

You entered: What a crazy message

Sorry - this message cannot be decoded using 123 Cipher.

Again? (Y/N)? n

Answer 1

Code:

import java.util.Scanner;

public class Main {
  
   // function take scanner object and returns input line
   public static String getUserInput(Scanner scnr){
       String line;
       String fullString="";
       //loop until empty line is entered
       while ((line = scnr.nextLine()).length() > 0)
       {
           fullString=fullString+line+"\n";
       }
       //returning concatenated string
       return fullString;
   }
  
   //function to decode the string. Takes scanner as input
   public static String decodeMessage(Scanner wordScanner) {
       //declaring variables
       String decodedValue="";
       int count=0;
       //loop while scanner has next words
       while(wordScanner.hasNext()){
           //getting first character and adding to decoded value
           try{//try catch for index errors
           decodedValue=decodedValue+wordScanner.next().charAt(count);
           count++;//increasing count to check the number of words
           if(count==3)
               break;
           }catch(Exception e){
               return null;
           }
          
       }
       //if count is 3 then input is correct
       if(count==3)
       return decodedValue;
       else //else return null
           return null;
   }
  
   //main function
   public static void main(String[] args) {
       //declaring variables
       String encodedText;
       String decodedText;
       char choice='Y';
       Scanner scnr =new Scanner(System.in);
      
       //loop while choice is not N or n
       while(choice!='n' && choice!='N'){
           //prompting for input
           System.out.println("Enter the encoded message on one or several lines. Enter an empty line when you are finished typing your message:");
           //setting encoded text
           encodedText=getUserInput(scnr);
           //if entered line is not empty continue or print error message  
           if(encodedText!=""){
               // print entered input
                   System.out.println("You entered:"+encodedText);
                   //creating scanner object to be used as tokernizer
                   Scanner lineTokenizer = new Scanner(encodedText);
                   decodedText=decodeMessage(lineTokenizer);//get decoded message
                   if(decodedText!=null){//if not null print decoded text
                       System.out.println("The decoded message is:"+decodedText);
                       System.out.print("Again? (Y/N)? ");
                   }else{
                       //if null print error message
                       System.out.println("Sorry - this message cannot be decoded using 123 Cipher. Again? (Y/N)?");  
                   }
                   //closing scanner object
                   lineTokenizer.close();
               }else{
                   //print error message for empty input
                   System.out.println("Sorry - this message cannot be decoded using 123 Cipher. Again? (Y/N)?");
               }
               //getting choice
               choice = scnr.nextLine().charAt(0);
               //loop while choice is not valid
               while(choice!='n' && choice!='N' && choice!='Y' && choice!='y'){
                   System.out.println("Please give valid choice");
                   choice = scnr.next().charAt(0);
               }
           }
       System.out.println("Program ended");
       scnr.close();  
   }
}

Output: