Newbish question - Exception loop?

[Dibbie]

First off, hello, im new to this forums, so hello to everyone! =D
Secondly, i know this is not the right area to post this, since this is a Java related issue, but it wont let me post in Java section, sais i dont have the rights to. Anyway, on to my question:

So, I made a program thats a simple calculator, and this is my first year programming (iv been useing Java and programming for a good 2 months now, im not in school for it)

Anyway, so the problem is that I donno how to loop it, so it works properly, heres whats suposto happen:
Enter your first number to add: g
That's not a number.
Enter your first number to add:

Heres what happens:
Enter your first number to add: g
That's not a number.
+
Enter your second number:

Here is my code, can someone please tell me what im doing wrong here:

if (op == 'A' || op == 'a')
{
while (exception==null)
{
write ("Enter your first number to add: ");
try
{
num1 = readInt ();
}
catch(Exception e)
{
System.out.println("That's not a number.");
exception=e.toString();
}
}
writeLine ("+");
write ("Enter your second number: ");
num2 = readInt ();
sum = num1 + num2;
writeLine (num1 + " + " + num2 + " = " + sum);
writeLine ("");
writeLine ("Back to menu? (Y|N)");
writeLine ("");
op = readChar ();
}

(Also, just so you understand the program, its a simple calculator that adds, subtracts, multiplys, or devides)
Dibbie Simple Calculator selected!

A (Add) S (Subtract) M (Multiply) D (Divide)

^ Above you pick wich option you want, in the error shown above, i picked A, add

[DemonWasp]

What's happening is that when you enter a non-number, the readInt() call fails and throws an exception (hopefully a NumberFormatException). Then, the 'exception' variable gets set to a string representing that exception, then exception is not null, so the loop does not continue. The more straightforward way to write this kind of thing is:

Java:

while ( true ) {     try {         num1 = readInt();         break;  // leaves the outer while loop immediately     } catch ( NumberFormatException e ) {         System.out.println ( "That is not a number." );     } }