Question

In Java please

Cipher.java:

/*
* Fix me
*/
import java.util.Scanner;
import java.io.PrintWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;

public class Cipher {

   public static final int NUM_LETTERS = 26;
   public static final int ENCODE = 1;
   public static final int DECODE = 2;

   public static void main(String[] args) /* FIX ME */ throws Exception {

    // letters
    String alphabet = "abcdefghijklmnopqrstuvwxyz";
      
    // Check args length, if error, print usage message and exit
    if (args.length != 3) {
        System.out.println("Usage:\n");
        System.out.println("java Cipher <filename> <cipher-key> <digit>\n");
        System.out.println("Options:\n");
        System.out.println("filename\tThe filename of the text file to open");
        System.out.println("cipher-key\tThe cipher key for encryption/decryption");
        System.out.println("digit\t\t1 to encode or 2 to decode");

        System.exit(1);
    }

    // Extract input args to variables
           String inputFilename = args[0];
           String key = args[1];
           int action = Integer.parseInt(args[2]);
           if(action != 1 && action != 2) {
               System.out.println("Option " + action + " is not valid");
               System.exit(1);
           }
           String outputFilename = getOutputFilename(inputFilename, action);
           Scanner input = openInput(inputFilename);
           PrintWriter output = openOutput(outputFilename);

    // Read in data and output to file
    // Convert all letters to lowercase for output
    StringBuilder message = new StringBuilder(input.useDelimiter("\\Z").next());

    for(int i = 0; i < message.length(); ++i) {
        int offset = key.charAt(i % key.length()) - 'a';
        if(action == 1) {
            message.setCharAt(i, shiftUpByK(message.charAt(i), offset));
        } else {
            message.setCharAt(i, shiftDownByK(message.charAt(i), offset));
        }
    }

    output.println(message.toString().toLowerCase());

           // Close streams
           input.close();
           output.close();

   }

   /**
   * Open input for reading
   *
   * @param filename
   * @return Scanner
   * @throws FileNotFoundException
   */
   public static Scanner openInput(String filename) throws FileNotFoundException {
       return new Scanner(new File(filename));
   }

  
   /**
   * Open output for writing
   *
   * @param filename
   * @return PrintWriter
   * @throws FileNotFoundException
   */
   static PrintWriter openOutput(String filename) throws FileNotFoundException {
       return new PrintWriter(new File(filename));
   }


/**
* Encode letter by some offset d
*
* @param c input character
* @param offset amount to shift character value
* @return char encoded character
*/
   public static char shiftUpByK(char c, int offset) {
       if ('a' <= c && c <= 'z')
           return (char) ('a' + (c - 'a' + offset) % NUM_LETTERS);
       if ('A' <= c && c <= 'Z')
           return (char) ('A' + (c - 'A' + offset) % NUM_LETTERS);
       return c; // don't encrypt if not an ic character
   }
  
   /**
* Decode letter by some offset d
*
* @param c input character
* @param offset amount to shift character value
* @return char decoded character
*/
   public static char shiftDownByK(char c, int offset) {
       if ('a' <= c && c <= 'z')
           return (char) ('a' + (((c - 'a' - offset) % NUM_LETTERS) + NUM_LETTERS ) % NUM_LETTERS);
       if ('A' <= c && c <= 'Z')
           return (char) ('A' + (((c - 'A' - offset) % NUM_LETTERS) + NUM_LETTERS ) % NUM_LETTERS);
       return c; // don't decrypt if not an ic character
   }

   /**
   * Changes file extension to ".coded" or ".decoded"
   *
   * @param filename
   * @return String new filename or null if action is illegal
   */
   public static String getOutputFilename(String filename, int action) {
       int indexOfExtension = filename.indexOf(".");
       String fileNameWithoutExtension;
       if(indexOfExtension != -1) {
           fileNameWithoutExtension = filename.substring(0, indexOfExtension);
       } else {
           fileNameWithoutExtension = filename;
       }

       if(action == 1) {
           return fileNameWithoutExtension + ".coded";
       } else {
           return fileNameWithoutExtension + ".decoded";
       }
   }


   public String getInfo() {
       return "Program 3, Student's name here";
   }

}

20.23 Program 5b: CipherEx catch exception

Instructor note:

The key is expected to be converted to lowercase before encoding/decoding.

Objectives

• Command line input
• File input and output
• Catching exceptions

Program Description

This program is identical to Cipher.java with these exceptions (no pun intended):

• You must catch the exceptions when opening the input and output files instead of rethrowing the error in the method headers. For this, your program must output 'Error opening file filename' and exit.
• You must catch the exceptions when an invalid option is entered for the parameter that decides if the program is to encode or decode. For this, your program must output 'Option option is not valid' and exit.
• You must catch the exceptions when the wrong number of arguments is passed. For this, your program must output 'Usage: Cipher inputFileName cipherKey (1)encode (2)decode' and exit.

Output

Test case 5 will display an error message:
Error opening file badFilename

Test case 6 will display an error message:
Usage: Cipher inputFileName cipherKey (1)encode (2)decode

The other test cases will be the same as the Cipher class.

Answer 1

I have implemented the updated code to handle the exception per the given description.

Please find the following Code Screenshot, Output, and Code.

ANY CLARIFICATIONS REQUIRED LEAVE A COMMENT

1.CODE SCREENSHOT :

2.OUTPUT :

3.CODE :

/*
* Fix me
*/
import java.util.Scanner;
import java.io.PrintWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;

public class Cipher {

   public static final int NUM_LETTERS = 26;
   public static final int ENCODE = 1;
   public static final int DECODE = 2;
   public static void main(String[] args) /* FIX ME */ throws Exception {
    // letters
    String alphabet = "abcdefghijklmnopqrstuvwxyz";
    // Check args length, if error, print usage message and exit
        try{
    if (args.length != 3) {
        throw new Exception();
    }
        }catch(Exception e){
                System.out.println("Usage: Cipher inputFileName cipherKey (1)encode (2)decode");
        System.exit(1);
        }

    // Extract input args to variables
           String inputFilename = args[0];
           String key = args[1];
           int action = Integer.parseInt(args[2]);
                   try{
           if(action != 1 && action != 2) {
              throw new Exception();
           }}catch(Exception e){
                            System.out.println("Option " + action + " is not valid");
               System.exit(1);
                   }
           String outputFilename = getOutputFilename(inputFilename, action);
           Scanner input = openInput(inputFilename);
           PrintWriter output = openOutput(outputFilename);

    // Read in data and output to file
    // Convert all letters to lowercase for output
    StringBuilder message = new StringBuilder(input.useDelimiter("\\Z").next());

    for(int i = 0; i < message.length(); ++i) {
        int offset = key.charAt(i % key.length()) - 'a';
        if(action == 1) {
            message.setCharAt(i, shiftUpByK(message.charAt(i), offset));
        } else {
            message.setCharAt(i, shiftDownByK(message.charAt(i), offset));
        }
    }

    output.println(message.toString().toLowerCase());

           // Close streams
           input.close();
           output.close();

   }

   /**
   * Open input for reading
   *
   * @param filename
   * @return Scanner
   * @throws FileNotFoundException
   */
   public static Scanner openInput(String filename) {
           Scanner s=null;
           try{
       s=new Scanner(new File(filename));
           }catch(FileNotFoundException e){
                        System.out.println("Error opening file "+filename);
                        System.exit(0);
           }return s;
   }

  
   /**
   * Open output for writing
   *
   * @param filename
   * @return PrintWriter
   * @throws FileNotFoundException
   */
   static PrintWriter openOutput(String filename) throws FileNotFoundException {
       return new PrintWriter(new File(filename));
   }


/**
* Encode letter by some offset d
*
* @param c input character
* @param offset amount to shift character value
* @return char encoded character
*/
   public static char shiftUpByK(char c, int offset) {
       if ('a' <= c && c <= 'z')
           return (char) ('a' + (c - 'a' + offset) % NUM_LETTERS);
       if ('A' <= c && c <= 'Z')
           return (char) ('A' + (c - 'A' + offset) % NUM_LETTERS);
       return c; // don't encrypt if not an ic character
   }
  
   /**
* Decode letter by some offset d
*
* @param c input character
* @param offset amount to shift character value
* @return char decoded character
*/
   public static char shiftDownByK(char c, int offset) {
       if ('a' <= c && c <= 'z')
           return (char) ('a' + (((c - 'a' - offset) % NUM_LETTERS) + NUM_LETTERS ) % NUM_LETTERS);
       if ('A' <= c && c <= 'Z')
           return (char) ('A' + (((c - 'A' - offset) % NUM_LETTERS) + NUM_LETTERS ) % NUM_LETTERS);
       return c; // don't decrypt if not an ic character
   }

   /**
   * Changes file extension to ".coded" or ".decoded"
   *
   * @param filename
   * @return String new filename or null if action is illegal
   */
   public static String getOutputFilename(String filename, int action) {
       int indexOfExtension = filename.indexOf(".");
       String fileNameWithoutExtension;
       if(indexOfExtension != -1) {
           fileNameWithoutExtension = filename.substring(0, indexOfExtension);
       } else {
           fileNameWithoutExtension = filename;
       }

       if(action == 1) {
           return fileNameWithoutExtension + ".coded";
       } else {
           return fileNameWithoutExtension + ".decoded";
       }
   }


   public String getInfo() {
       return "Program 3, Student's name here";
   }

}