C8Ex12CaptainCrunch3

public class C8Ex12CaptainCrunch3 {
	
	public static char convert(String dict, int i, int n) {
		if (n >= 0) {
			if (i+n < 26) {
				return dict.charAt(i+n);
			} else {
				return dict.charAt(i+n-26);
			}
		} else {
			if (i+n > 0) {
				return dict.charAt(i+n);
			} else {
				return dict.charAt(i+n+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 = "I dont want to tell you how to dO it";
		System.out.println(encode(s, 15));
	}

}