im sorry ive posted a question yesterday in filipino language (specially to ate padme).. actually, i konw the rule but this my problem cause me to 4get it.. nyweiz, here's my problem cracking my skull. we have our homework in java programming to compute grades.. ive constructed it all except for one,, what if the user or my professor just enter the dialog box (JOptionPane.showInputdialog) or just enter without input of any grade (without typing the grade).. or enter characters instead of numbers.. how can i create an error message warning the user that he should enter valid numbers.. tnx again,.,.