JOptionPane Printing From A For Loop?

I am writing a program that has to do with ciphers and cipher shifts. The program itself works fine, but I am having trouble printing out the answers to JOptionPane. I know the basics of JOptionPane, but my problem is this:

Majority of my program takes place in a for loop, and resolves the cipher (it is a basic cipher program) 1 digit at a time. So, only the last DIGIT (I don't know how to convert a digit to a CHAR in JOptionPane) is printed to JOptionPane. Here is my code:

public static void main(String[] args) {
String cipher = JOptionPane.showInputDialog(null,
"Please enter a sentence or word that you wish to encode or decode. This program uses " + " a basic cipher shift.");
int answer = 0;
String upperCase = cipher.toUpperCase();
char[] cipherArray = cipher.toCharArray();

[Code] .......