Question

[Java] Create a class called FileExercises that contains the following method

• Method encrypt that does not return anything and takes a shift, input filename and output filename as arguments. It should read the input file as a text file and encrypt the content using a Caesar cypher with the shift provided. The resulting text should be placed in the output file specified. (If the output file already exists, replace the existing file with a new file that contains the required content.) You can find a description of the Caesar cypher on-line. If a character in the file is not alphabetic, leave the character unchanged. Convert upper case character to upper case characters and lower case characters to lower case characters.

Answer 1

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

public class FileExercises {

   // function to encrypt input file and store the result in output

   public static void encrypt(int shift, String inputFileName, String outputFileName) {

       try {
           File inputFile = new File(inputFileName); // input file object
           File outputFile = new File(outputFileName); // output file object
           FileReader fileReader = new FileReader(inputFile);
           FileWriter fileWriter = new FileWriter(outputFile);
           BufferedReader bufferedReader = new BufferedReader(fileReader);
           BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
           String line;
           while ((line = bufferedReader.readLine()) != null) { // read file line by line
               bufferedWriter.write(encryptHelper(line, shift).toString()); // encrypt line by line and write to output
                                                                               // file
               bufferedWriter.write("\n");
           }
           fileReader.close();
           bufferedWriter.close();
           fileWriter.close();
           System.out.println("File encrypted successfully");

       } catch (IOException e) {
           e.printStackTrace();
       }

   }

   // helper function to encrypt text
   public static StringBuffer encryptHelper(String text, int shift) {
       StringBuffer result = new StringBuffer();

       for (int j = 0; j < text.length(); j++) {
           if (Character.isAlphabetic(text.charAt(j))) { // check if current character is alphabet
               if (Character.isUpperCase(text.charAt(j))) {
                   char character = (char) (((int) text.charAt(j) + shift - 65) % 26 + 65); // shift character by shift
                                                                                               // times
                   result.append(character);
               } else {
                   char character = (char) (((int) text.charAt(j) + shift - 97) % 26 + 97); // shift character by shift
                                                                                               // times
                   result.append(character);
               }
           } else {
               result.append(text.charAt(j)); // if not alphabet add character as it is
           }
       }
       return result;
   }

   public static void main(String... args) {
       String inputFileName, outputFileName;
       int shift;
       Scanner scan = new Scanner(System.in);
       System.out.println("Enter input file name");
       inputFileName = scan.nextLine(); // ask for input file name
       System.out.println("Enter output file name");
       outputFileName = scan.nextLine(); // ask for output file name
       System.out.println("Enter shift for caesar cipher");
       shift = scan.nextInt(); // ask for shift

       encrypt(shift, inputFileName, outputFileName); // call encrypt function

   }

}
//output