Tutorial One Time Pad (Vernam Cipher) Algorithm

public class OtpByVaultree {// Method 1// Returning encrypted textpublic static String stringEncryption(String text,                                      String key){    // Initializing cipherText    String cipherText = "";    // Initialize cipher array of key length    // which stores the sum of corresponding no.'s    // of plainText and key.    int cipher[] = new int[key.length()];    for (int i = 0; i < key.length(); i++) {        cipher[i] = text.charAt(i) - 'A'                + key.charAt(i)                - 'A';    }    // If the sum is greater than 25    // subtract 26 from it    // and store that resulting value    for (int i = 0; i < key.length(); i++) {        if (cipher[i] > 25) {            cipher[i] = cipher[i] - 26;        }    }    // Converting the no.'s into integers    // Convert these integers to corresponding    // characters and add them up to cipherText    for (int i = 0; i < key.length(); i++) {        int x = cipher[i] + 'A';        cipherText += (char)x;    }    // Returning the cipherText    return cipherText;}// Method 2// Returning plain textpublic static String stringDecryption(String s,                                      String key){    // Initializing plain text    String plainText = "";    // Initializing integer array of key length    // which stores difference    // of corresponding no.'s of    // each character of cipherText and key    int plain[] = new int[key.length()];    // Running for loop for each character    // subtracting and storing in the array    for (int i = 0; i < key.length(); i++) {        plain[i]                = s.charAt(i) - 'A'                - (key.charAt(i) - 'A');    }    // If the difference is less than 0    // add 26 and store it in the array.    for (int i = 0; i < key.length(); i++) {        if (plain[i] < 0) {            plain[i] = plain[i] + 26;        }    }    // Converting int to corresponding char    // add them up to plainText    for (int i = 0; i < key.length(); i++) {        int x = plain[i] + 'A';        plainText += (char)x;    }    // Returning plainText    return plainText;}// Method 3// Main driver methodpublic static void main(String[] args){    // Declaring plain text    String plainText = "VAULTREE";    // Declaring key    String key = "AXDHCGQK";    // Converting plain text to toUpperCase    // function call to stringEncryption    // with plainText and key as parameters    String encryptedText = stringEncryption(            plainText.toUpperCase(), key.toUpperCase());    // Printing cipher Text    System.out.println("Cipher Text - "            + encryptedText);    // Calling above method to stringDecryption    // with encryptedText and key as parameters    System.out.println(            "Message - "                    + stringDecryption(encryptedText,                    key.toUpperCase()));}}