C8Ex12CaptainCrunch4

public class C8Ex12CaptainCrunch4 {
	
	public static char convert(String dict, int i, int n) {
		if (i+n > 0) {
			return dict.charAt((i+n) % 26);
		} else {
			return dict.charAt(((i+n) % 26 + 26) % 26);
		}
	}
	
	public static String encode(String s, int n) {
		String d = "abcdefghijklmnopqrstuvwxyz";
		String D = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
		int i = 0;
		String box = "";
		while (i < s.length()) {
			if (s.charAt(i) == ' ') {
				box = box + ' ';
			} else {
				int j = d.indexOf(s.charAt(i));
				if (j != -1) {
					box = box + convert(d, j, n);
				} else {
					j = D.indexOf(s.charAt(i));
					box = box + convert(D, j, n);
				}
			}
			i = i + 1;
		}
		return box;
	}

	public static void main(String[] args) {
		String s = "H Chc Hs ehmzkkx";
		System.out.println(encode(s, -51));
	}
}