help with joption pane cancel button

I am almost there with this one!
The book tells me to use a while loop unless the user clicks the cancel button but does not tell me what what code to enter to end the program if they do hit cancel button. I need to end the program at that point but don't know how. Is this the action listener? I am confused. Please help-Thanks

import javax.swing.JOptionPane;
 
public class MyTypeb
{
 
public static void main(String[] args)
{
// declare and construct variables

int choice = 0;
int tryInt = 0;
double tryDouble;
boolean done = false;
 
// loop while user does not click cancel button
while(!done) {
try{
String strChoice = JOptionPane.showInputDialog(null,"What's My Type?\n1)String\n2)integer\n3)double\n4Quit the program\n");
choice = Integer.parseInt(strChoice);
switch(choice) {
case 1:
JOptionPane.showMessageDialog(null, "Correct, any input can be saved as a String");
break;
case 2:
JOptionPane.showMessageDialog(null, "Correct");
//tryInt = Integer.parseInt(strChoice);
break;
case 3:
JOptionPane.showMessageDialog(null, "Correct");
//tryDouble = Integer.parseInt(strChoice);
break;
case 4:
done = true;
JOptionPane.showMessageDialog(null, "Now Closing");
break;
default:
throw new NumberFormatException();
 
}
}
catch(NumberFormatException e) {
JOptionPane.showMessageDialog(null, "Please try again");
}
}
 
System.exit(0);
 
}
 
}

the way you have your program now, 'cancel' will crash the program

when using a showInputDialog(), any of 'cancel', 'esc' or 'X' (top right corner)
will return null. your next line will then try to parse a null object

perhaps the easiest way to handle it is to check for null

String strChoice = JOptionPane.showInputDialog(...);
if(strChoice == null) break;//<-------------------------break out of the 'while'
choice = Integer.parseInt(strChoice);

[EDIT]
just re-read this and now noticed the try/catch, so it won't crash, but
checking for null would still be a simple way to handle it
[ October 17, 2006: Message edited by: Michael Dunn ]