java cipher final

package javaapplication2;
import java.util.Scanner;

class abc {
    private static String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    private static int index;
    private static int updated_index;
    private static int final_index;
    private static int index_p_t_l; // untuk plaintext
    private static int index_s_t_l; // untuk ciphertext
    private static String plaintxt;
    private static String ciphertxt;
    private static String finaltext;


    public static String encrypt(String plainText, int encryptionKey){
        reset();
        plainText = plainText.toUpperCase();

        for (index =0 ; index < plainText.length() ;index++ ){


            if ( plainText.charAt(index) != ' '){
                index_p_t_l = alphabet.indexOf(plainText.charAt(index));

                updated_index = encryptionKey + alphabet.indexOf(plainText.charAt(index));

                if (updated_index >= alphabet.length()){
                    final_index = updated_index - alphabet.length();
                }else{
                    final_index = updated_index;
                }

                ciphertxt = alphabet.substring(final_index, final_index +1);

                finaltext = finaltext + ciphertxt;
            }else{
            }

        }
        return finaltext;
    }



    public static String decrypt(String cipherText, int decryptionKey){
        reset();
        cipherText = cipherText.toUpperCase();

        for ( index =0 ; index < cipherText.length() ;index++ ){


            if ( cipherText.charAt(index) != ' '){
                index_p_t_l = alphabet.indexOf(cipherText.charAt(index));


                index_s_t_l = index_p_t_l;
                updated_index =  alphabet.indexOf(cipherText.charAt(index)) - decryptionKey;

                if (updated_index < 0)
                {
                    final_index = updated_index + alphabet.length();
                }else{
                    final_index= updated_index;
                }
                plaintxt = alphabet.substring(final_index,final_index+1);

                finaltext=finaltext+plaintxt;
            }
            else
            {
            }
        }
        return finaltext;
    }

    private static void reset(){
        finaltext = " ";
    }
}



 class cipher1 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        while(true){
           System.out.print("text untuk di encrypt: ");
            String plain_text = scan.next();
            System.out.print("encryption key(harus 0 - 25): ");
            int encryption_key = scan.nextInt();
            System.out.println(abc.encrypt(plain_text,encryption_key));

            System.out.print("text untuk di decrypt: ");
            String cipher_text = scan.next();
            System.out.print("encryption key(harus sama seperti sebelum nya): ");
            int decryption_key = scan.nextInt();
            System.out.println(abc.decrypt(cipher_text,decryption_key));
        }

    }

    }