Combining Characters Into A String

So what my program is supposed to do is take a number inputted by the use and then take a phrase. It then changes that phrases letter by the number inputted prior for example if you type in 2 as your int and Hello as your phrase you should get JGNNQ, which i can do. but the problem is that when i run it, it outputs like this:

J
G
N
N
Q

As separate characters how can I combine those characters in 1 string so it looks like JGNNQ? this is my code

import java.util.Scanner;
public class Dcod_MAin {
private static final Object[] String = null;
public static void main(String[] args){
Scanner input = new Scanner (System.in);
System.out.println("What is the day of the month");
int shift;

[Code] ....