Encryption with shift cipher algorithm.

ShiftCipher.java

package examples;

/**
 * Created by Gökhan on 11/14/2014.
 */
public class ShiftCipher {

    private int key;
    public static final int ALPHABET_LEN = 26;

    public ShiftCipher(int key) {
        this.key = key;
    }

    public String getEncryptedText(String msg) {
        if (msg == null) return null;

        char[] chars = msg.toCharArray();
        StringBuilder sb = new StringBuilder();

        for (char c : chars) {
            sb.append(getEncryptedChar(c));
        }

        return sb.toString();
    }

    private char getEncryptedChar(char c) {

        int base = (int) 'a';
        int pos = (int) c;
        int diff = pos - base;
        int shifted = (diff + key) % ALPHABET_LEN;
        int result = shifted + base;

        return (char) result;
    }

    public String getDecryptedText(String msg) {
        if (msg == null) return null;

        char[] chars = msg.toCharArray();
        StringBuilder sb = new StringBuilder();

        for (char c : chars) {
            sb.append(getDecryptedChar(c));
        }

        return sb.toString();
    }

    private char getDecryptedChar(char c) {
        int base = (int) 'a';
        int pos = (int) c;
        int diff = pos - base;
        int shifted = (diff - key);

        if (shifted < 0)
            shifted+= ALPHABET_LEN;

            int result = shifted + base;

        return (char)result;
    }


}