Шифрование методом Цезаря

// Caesar.java: implement the Caesar cipher
//   This carries out a simple rotation of lower-case letters,
//   and does nothing to all other characters, making the decryption
//   process even easier, because caps and punctuation marks survive unchanged.
//   Usage: java Caesar (-d | -e) key
//   Above, option "-d" is for decryption, while "-e" is for encryption
import java.io.*;
public class Caesar {
   private Reader in; // standard input stream for message
   private int key; // (en|de)cryption key
 
   // Caesar: constructor, opens standard input, passes key
   public Caesar(int k) {
      // open file
      in = new InputStreamReader(System.in);
      key = k;
   }
   // (en|de)crypt: just feed in opposite parameters
   public void encrypt() { translate(key); }
   public void decrypt() { translate(-key); }
 
   // translate: input message, translate
   private void translate(int k) {
      char c;
      while ((byte)(c = getNextChar()) != -1) {
         if (Character.isLowerCase(c)) {
            c = rotate(c, k);                
         }
         System.out.print(c);
      }
   }
 
   // getNextChar: fetches next char.
   public char getNextChar() {
      char ch = ' '; // = ' ' to keep compiler happy
      try {
         ch = (char)in.read();
      } catch (IOException e) {
         System.out.println("Exception reading character");
      }
      return ch;
   }
   // rotate: translate using rotation, version with table lookup
   public char rotate(char c, int key) { // c must be lowercase
      String s = "abcdefghijklmnopqrstuvwxyz";
      int i = 0;
      while (i < 26) {
          // extra +26 below because key might be negative
          if (c == s.charAt(i)) return s.charAt((i + key + 26)%26);
             i++;
      }
      return c;
   }
 
 
   // main: check command, (en|de)crypt, feed in key value
   public static void main(String[] args) {
      if (args.length != 2) {
         System.out.println("Usage: java Caesar (-d | -e) key");
         System.exit(1);
      }
      Caesar cipher = new Caesar(Integer.parseInt(args[1]));
      if (args[0].equals("-e")) cipher.encrypt();
      else if (args[0].equals("-d")) cipher.decrypt();
      else {
         System.out.println("Usage: java Caesar (-d | -e) key");
         System.exit(1);
      }
   }
}