FileEncryptionDecryption.java

import java.io.*;
import java.util.Scanner;

public class FileEncryptionDecryption {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.println("File Encryption/Decryption");
        System.out.print("Enter E for Encryption or D for Decryption: ");
        char choice = sc.next().toUpperCase().charAt(0);

        sc.nextLine(); // Consume newline

        System.out.print("Enter input file name (e.g., input.txt): ");
        String inputFile = sc.nextLine();

        System.out.print("Enter output file name (e.g., output.txt): ");
        String outputFile = sc.nextLine();

        try {
            BufferedReader reader = new BufferedReader(new FileReader(inputFile));
            BufferedWriter writer = new BufferedWriter(new FileWriter(outputFile));

            String line;

            while ((line = reader.readLine()) != null) {
                String result = "";

                for (int i = 0; i < line.length(); i++) {
                    char ch = line.charAt(i);

                    if (choice == 'E') {
                        result += (char) (ch + 3); // Encrypt
                    } else if (choice == 'D') {
                        result += (char) (ch - 3); // Decrypt
                    }
                }

                writer.write(result);
                writer.newLine();
            }

            reader.close();
            writer.close();

            if (choice == 'E') {
                System.out.println("File encrypted successfully!");
            } else if (choice == 'D') {
                System.out.println("File decrypted successfully!");
            } else {
                System.out.println("Invalid choice!");
            }

        } catch (IOException e) {
            System.out.println("Error: " + e.getMessage());
        }

        sc.close();
    }
}