Making string as a secret mode

stringMystery

import java.util.*;
import java.lang.*;

class Main {
	
	 public static String reverseString(String s) {
    return ( new StringBuffer(s) ).reverse().toString();
  }

  public static void main(String[] args) {
		
		
		char listAlpha[] = new char[26];
		int listInt[] = new int[26];
		for(int i = 0 ; i < 26 ; i++){
			listInt[i] = i;
		}
		String alpha = "abcdefghijklmnopqrstuvwxyz";
		
		
		Scanner sc = new Scanner(System.in);
		String temp1 = sc.next();
		System.out.println("입력한 단어 : " + temp1);
		
		
		//정방향으로 입력받은 단어의 번호를 구하기
		String word = "";
		for(int i = 0 ; i < temp1.length() ; i++){
			word += alpha.indexOf(temp1.charAt(i));
  	}
		System.out.println(word);
		System.out.println();
		
		// 역방향으로 단어를 뒤집기
		String temp2 = reverseString(temp1);
		System.out.println("뒤집은 단어 : " + temp2);
		String word2 = "";
		for(int i = 0 ; i < temp2.length() ; i++){
			word2 += alpha.indexOf(temp2.charAt(i));
  	}
		System.out.println(word2);
		System.out.println();
		int temp3 = Integer.parseInt(word) + Integer.parseInt(word2);
		String word3 = Integer.toString(temp3);
		System.out.println("암호화된 숫자 : " + word3);


		// 암호화된 숫자를 암호화된 문자로 변경
		String final_word ="";
		if (word3.length()%2 == 0){
			for(int i = 0 ; i < word3.length() ; i += 2){
				//System.out.println(word3.substring(i,i+2));
				final_word += alpha.charAt(Integer.parseInt(word3.substring(i,i+2))%26);
			}
		}
		else if(word3.length()%2 == 1){
				for(int i = 0 ; i < word3.length()-1 ; i += 2){
				//System.out.println(word3.substring(i,i+2));
				final_word += alpha.charAt(Integer.parseInt(word3.substring(i,i+2))%26);
			}
			final_word += alpha.charAt(Integer.parseInt(word3.substring(word3.length()-1));
			
		}

		System.out.println();
		System.out.println(final_word);
		
}
}