vignere decipher java

// program to implement vignere cipher decryption
/**
 * Created by MOHIT on 28-09-2017.
 */
import java.io.File;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.Random;
import java.io.FileWriter;

public class vignereDecipher {

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

        //System.out.print("Enter the String to be decrypted : ");
        //String inString = sc.nextLine();

        System.out.print("\nEnter the Decription key : ");
        String key = sc.nextLine();

        // String finalString = decrypt_(inString,cipher);
        decrypt_file(key);
        // System.out.print("\nThe decrypted String is : " + finalString);
    }

    // method that removes all the numbers and punctuations
    static String remove_ichars(String original_msg){
        original_msg = original_msg.replaceAll("[^A-Z\n\r]", "");
        return original_msg;
    }

    // method that accepts encrypted string and returns decrypted string
    static String decrypt(String original_msg, String key){

// allchars is our keyspace
        String allChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        int all_chars_length = allChars.length();
        String decrypted_msg = "";

        // converting our string to uppercase
        original_msg = original_msg.toUpperCase();
        // removing all numbers, punctuations
        original_msg = remove_ichars(original_msg);
        // converting key to uppercase
        key = key.toUpperCase();
        int index = 0;

        // iterating over the original message character by character and decrypting it and appending it to the new string
        for(int i=0; i< original_msg.length(); i++){
            Character letter = original_msg.charAt(i);
            if(allChars.indexOf(letter) >= 0) {
                int position = (allChars.indexOf(letter) - allChars.indexOf(key.charAt(index)) + 26) % all_chars_length;
                Character e_letter = allChars.charAt(position);
                decrypted_msg += e_letter;
                index++;
                // reset index if it is greater that key length
                if(index >= key.length()){
                    index %= key.length();
                }
            // case when \n or \r is encountered
            }else{
                decrypted_msg += letter;
                index = 0;
            }
        }

        return decrypted_msg;
    }

    // method that decrypts file
    static void decrypt_file(String key){
        FileInputStream fin;
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter the path of the file : ");
        String file_name = sc.nextLine();
        String fullFile = "";

        try {
            fin = new FileInputStream(file_name);
            Scanner fp = new Scanner(fin);
            int size = 0;

            while (fp.hasNextLine()) {
                String line = fp.nextLine();
                fullFile += line + "\n";
                size += line.length();
            }
            System.out.println(fullFile);
            System.out.println("File read successfully!!");
            fullFile = decrypt(fullFile, key);
            System.out.println("Data decrypted successfully!!");
            System.out.println(fullFile);
        }catch (Exception e){
            e.printStackTrace();
        }


        try {

            File newTextFile = new File("C:\\Users\\MOHIT\\Desktop\\decrypted_file.txt");
            FileWriter f1 = new FileWriter(newTextFile);
            f1.write(fullFile);
            f1.close();
            System.out.println("decrypted file stored on Desktop");
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }


}

/*
Output for decrypting a file


Enter File name :F:/python_3.4/sample.txt
Enter File name : F:/python_3.4/sample.txt
File read successufully!!
File data decrypted successfully!!
decrypted file stored on Desktop!!


 */