Mine

private void inchButtonActionPerformed(java.awt.event.ActionEvent evt) {                                                   String s = inchField.getText();        try {            double inch = Double.parseDouble(s);            inch = inch*100;            int inch2 = (int)inch;            cmField.setText(""+Harjoitus2.inchesToCm(inch));        } catch (NumberFormatException ex) {            JOptionPane.showMessageDialog(this, "You must input a number",                    "Invalid input", JOptionPane.ERROR_MESSAGE);        }    }