CaesarCipher

This program does a simple encryption using a Caesar cipher. It shifts each letter in the alphabet to the letter 2 positions later in the alphabet.

import objectdraw.*;

/**
 * @author Barbara Lerner
 * @version April 7, 2008
 *
 * Encrypts the word "Hello" using the Caesar Cipher.  The Caesar Cipher
 * shifts letters 2 positions, replacing a with c, b with d, etc.
 */
public class CaesarCipher extends WindowController {
    // The highest character value 
    private static final char MAX_CHAR = '~';
    
    // The lowest character value
    private static final char MIN_CHAR = ' ';
    
    // The range of characters 
    private static final int RANGE = MAX_CHAR - MIN_CHAR + 1;
    
    // The number of positions the text is shifted.
    private static final int KEY = 6;
    
    // The letter substitutions
    private char[] substitutions = new char[RANGE];
    
    /**
     * Display the original text and the encrypted text.
     */
    public void begin () {
        char c = MIN_CHAR;
        
        for (int i = RANGE - KEY; i < RANGE; i++) {
            substitutions[i] = c;
            c++;
        }
        for (int i = 0; i < RANGE - KEY; i++) {
            substitutions[i] = c;
            c++;
        }
        
        for (int i = 0; i < RANGE; i++) {
            System.out.print (substitutions[i]);
        }
        
        String unencryptedText = "Hello";
        String encryptedText = encrypt (unencryptedText);
        new Text ("Unencrypted text:  " + unencryptedText, 0, 0, canvas);
        new Text ("Encrypted text:  " + encryptedText, 0, 20, canvas);
    }
    
    /**
     * Encrypt the string using the Caesar cipher.  This shifts the characters by
     * 2 in the alphabet
     *
     * @param text the text to encrypt
     * @return the encrypted text
     */
    private String encrypt(String text) {
        String encodedText = "";
        for (int i = 0; i < text.length(); i++) {
            char nextChar = text.charAt(i);
            char nextEncodedChar = substitutions[nextChar - MIN_CHAR];
            encodedText = encodedText + nextEncodedChar;
        }
        return encodedText;
    }

}