The Caesar cipher is a simple form of encryption described HERE Of course, it should not be used for anything serious as it's pretty easily breakable. Below is an implementation in Java. The source is HERE

public class Caesar {
    public static void main(String[] args) {
        Caesar c = new Caesar();

        // Plaintext
        String text = args[0];

        // Distance to shift
        int shiftDistance = Integer.parseInt(args[1]);

        for (int i = 0; i < text.length(); i++) {
            System.out.print(c.rotate(text.charAt(i), shiftDistance));
        }
    }

    public char rotate(char c, int shiftDistance) {
        // Keep shift within bounds of alphabet
        shiftDistance %= 26;

        // Only rotate Latin alphabet and only letters
        if ((c >= 'a') && (c <= 'z')) {
            c += shiftDistance;

            if (c > 'z') {
                // correct overflow
                c = (char) ((c - 'z' + 'a') - 1);
            } else if (c < 'a') {
                // correct underflow
                c = (char) (('z' + c) - 'a' + 1);
            }
        } else if ((c >= 'A') && (c <= 'Z')) {
            c += shiftDistance;

            if (c > 'Z') {
                c = (char) ((c - 'Z' + 'A') - 1);
            } else if (c < 'A') {
                c = (char) (('Z' + c) - 'A' + 1);
            }
        }

        return c;
    }
}