How convert from vigenere to Columnar cipher ?

 package vigenere;
import java.util.Scanner;
public class VigenereCipher {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("Please enter the key (ONLY CAPITAL LETTERS WITHOUT SPACE)");
        String key = input.nextLine();
        System.out.println("Please enter the text");
        String plainText = input.nextLine(); 
        String e = encryption(plainText, key);
        System.out.println("encryption text is:");
        System.out.println(e);
        System.out.println("decryption text is:");
        System.out.println(decryption(e, key));
    }
 
    static String encryption(String plainText,  String key) {
        String empty = "";
        plainText = plainText.toUpperCase();
        for (int i = 0, j = 0; i < plainText.length(); i++) {
            char x = plainText.charAt(i);
            if (x < 'A' || x > 'Z') {};
            empty += (char)((x + key.charAt(j) - 2 * 'A') % 26 + 'A');
            j = ++j % key.length();
        }
        return empty;
    }
 
    static String decryption(String plainText,  String key) {
        String empty = "";
        plainText = plainText.toUpperCase();
        for (int i = 0, j = 0; i < plainText.length(); i++) {
            char x = plainText.charAt(i);
            if (x < 'A' || x > 'Z') {};
            empty += (char)((x - key.charAt(j) + 26) % 26 + 'A');
            j = ++j % key.length();
        }
        return empty;
    }
}