Control if it is a input

[Torgero]

What I am having problems with is that I need to put in a number (the number of the account), and if there is no input then the text "you have to enter a number".. The problem is that i dont know which method to use to control if a number is written in or not.. This is what i tried:

String TallLest = showInputDialog("LEDETEKST");
long kontoNummer = Long.parseLong(TallLest);
		while (kontoNummer == null || kontoNummer.trim().equals("")){
			showMessageDialog(null, "Du må legge inn.");
			kontoNummer = showInputDialog("What, what, what...");

		}

[Webuser]

kontoNummer = showInputDialog("What, what, what...");

modify as...

kontoNummer = showInputDialog(null,"What, what, what...");

[Webuser]

And what about

javax.swing.JOptionPane

importing ?