public String codieren(String plainT, char key) {
  String cipher = "";
  int len = plainT.length();
  char plainCh;
  char ciphCh = ' ';
  for (int i = 0; i < len; i++) {
    plainCh = plainT.charAt(i);
    if ((plainCh >= 'A') && (plainCh <= 'Z')) {
      ciphCh = (char)(plainCh - 'A' + key)
      if(ciphCh > 'Z') {
        ciphCh = (char)(ciphCh - 'Z' - 1 + 'A');
      }
      cipher = cipher + ciphCh;
    }
  }
  return cipher;
}