Refresh Window

Question

Hello,
Is it possible to relaunch a jar application or refresh the window if a user fails to enter something in a text field.
I can use an error trap but so far all I have created is an endless loop into a JOptionPane which is not good.

Answer 1

Ok, I think I figured out a way to do it by using a switch to break out of the loop but not sure if this is good practice or what.
I have:
String expr = codeIn.getText();
int myswitch = 1;
switch (myswitch) {
     case 1:
if (expr.length()<1) {
JOptionPane.showMessageDialog(this, "Eggs aren't supposed to be green.", "Inane error", JOptionPane.ERROR_MESSAGE);
break;
} else {
          //rest of code here
This has the desired result. However another slight problem is the if statement. This works OK but if I use
if (expr == null) it doesnt get caught.
I am getting this error in debug in NetBeans.