need help with Java programming language

This program is for encrypting and decrypting files. it's already done and it works only if the user inputs the right extension for the file

if the user in encrypting they should put the .txt extension after the file name and if the user is decrypting they should put the extension .enc after the file name but if the user put file name without extension the program terminates.

the program is supposed to show an error message "Wrong file extension" and return to the menu again when the user enters the file name without an extension. it should be for both encrypting and decrypting.

Here is the code.

--------------------------------------------------------------------------------------------------------

import java.io.File;

import java.io.FileNotFoundException;

import java.io.PrintWriter;

import java.util.Scanner;

public class Project{

/**

*

* Method to get input from user

*

*/

public static int getMenuOption() {

Scanner in = new Scanner(System.in);

int choi;

// asking the user to input what the want

while (true) {

System.out.println("1.Encrypt");

System.out.println("2.Decrypt");

System.out.println("3.Quit");

System.out.print("What would you like to do? ");

choi = in.nextInt();

if (choi < 1 || choi > 3) {

// if choice is not valid

System.out.println("Invalid choice, try again!");

}

else

break;

}

return choi;// returning choice

}

//this method is to encrypt file

public static void encrypt(File inputFile, int key) throws FileNotFoundException {

//getting the file name from the user

String fileName = inputFile.getName().trim();

//checking for txt extension using string method

if (!fileName.trim().split("\\.")[1].equals("txt")) {

System.out.println("Inavlid file ");

// returning to menu

return;

}

else {

//reading the file

Scanner fileReader = new Scanner(inputFile);

//changing the extension for the file to enc

String outputFile = fileName.split("\\.")[0] + ".enc";

File outFile = new File(outputFile);

PrintWriter writer = new PrintWriter(outputFile);

while (fileReader.hasNext()) {

//reading line by line

String ww = fileReader.nextLine();

String enc_string = "";

//using for loop encoding the string

for (int i = 0; i < ww.length(); i++) {

int ascii = (int) ww.charAt(i);

ascii = ascii + key;

enc_string = enc_string + (char) ascii;

}

//Writing the encrypted string to out put file

writer.write(enc_string + " ");

writer.flush();

}

System.out.println("Encrypted successfully !");

}

}

/**

*

* this method is for decrypting the file

*/

public static void decrypt(File inputFile, int key) throws FileNotFoundException {

//getting the file name for decrypted

String fileName = inputFile.getName().trim();

//checking for file extension .enc

if (!fileName.trim().split("\\.")[1].equals("enc")) {

System.out.println("Inavlid file ");

// returning to main

return;

}

else {

Scanner fileReader1 = new Scanner(inputFile);

//creating the file name ended with .txt

String outputFileName = fileName.split("\\.")[0] + ".txt";

File outFile = new File(outputFileName);

PrintWriter writer = new PrintWriter(outFile);

while (fileReader1.hasNext()) {

//reading file line by line

String t = fileReader1.nextLine();

//decrypting the string using for loop

String dec_string = "";

for (int i = 0; i < t.length(); i++) {

int rrr = (int) t.charAt(i);

rrr = rrr - key;

dec_string = dec_string + (char) rrr;

}

//writting to file

writer.write(dec_string + " ");

writer.flush();

}

System.out.println("Decrypted successfully");

}

}

// Main method for executing program

public static void main(String[] args) throws FileNotFoundException {

Scanner in = new Scanner(System.in);

while (true) {

int choice = getMenuOption();

if (choice == 1) {

System.out.print("Enter the file Name : ");

String filenamee = in.next();

System.out.print("Entet the shift key : ");

int key = in.nextInt();

encrypt(new File(filenamee), key);

}

else if (choice == 2) {

System.out.print("Enter the file Name : ");

String filenamee = in.next();

System.out.print("Entet the shift key : ");

int key = in.nextInt();

decrypt(new File(filenamee), key);

}

else if (choice == 3) {

System.exit(0);

}

}

}

}