Rot13 in Java using Lambdas

Main.java

package net.wjlafrance.lambdarot13;

import java.util.stream.Collectors;

/**
 * Created by lafrance on 3/25/14.
 */
public class Main
{

    /**
     * Performs rot13 encoding using a functional paradigm. The string's characters are streamed, mapped to their
     * rot13 value, and collected.
     */
    private static String rot13functional(String s) {
        return s.chars().mapToObj((c) -> String.valueOf((char) (
                (c >= 'A' && c <= 'M') || (c >= 'a' && c <= 'm') ? (c + 13) :
                (c >= 'N' && c <= 'Z') || (c >= 'n' && c <= 'z') ? (c - 13) : c))
            ).collect(Collectors.joining());
    }

    /**
     * Performs rot13 encoding using an imperative paradigm. The string is iterated over, character by character. Each
     * character is transformed and added to a StringBuffer.
     */
    private static String rot13imperative(String s) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if ((c >= 'A' && c <= 'M') || (c >= 'a' && c <= 'm')) {
                c += 13;
            } else if ((c >= 'N' && c <= 'Z') || (c >= 'n' && c <= 'z')) {
                c -= 13;
            }
            sb.append(c);
        }
        return sb.toString();
    }

    public static void main(String args[]) {
        System.out.println(rot13functional("Hello world! Lambdas are awesome!"));
        System.out.println(rot13imperative("Hello world! Lambdas are awesome!"));
    }

}