Question

I was struggling to get int values from a column in a database into a combo box, so that once selected the values would print out in a textbox when I deviced this solution:

private void jComboBoxSNActionPerformed(java.awt.event.ActionEvent evt) {                                            

    JComboBox jComboBoxSN = (JComboBox) evt.getSource();
    int s_n = (Integer) jComboBoxSN.getSelectedItem();
    System.out.println("Number: " + s_n);
}

I want to know, this acceptable programming or bad programming?

Answer 1

Unless you are certain that your combo box cannot contain null values (and this is uncertain if you are loading the values from a database), then the code you have shown is not safe. This line:

int s_n = (Integer) jComboBoxSN.getSelectedItem();

will result in a NullPointerException if executed on a null item. (Auto-unboxing a null primitive wrapper is a NullPointerException).

An alternative would be to check for null before converting Integer to int:

Integer i = (Integer)jComboBoxSN.getSelectedItem();
if (i != null) {
    int s_n = i;  // or s_n = i.intValue();
}

However, I think something like this would be more suitable:

    final JTextArea text = new JTextArea();
    JComboBox combo = new JComboBox();
    combo.addItemListener(new ItemListener() {
        @Override
        public void itemStateChanged(ItemEvent e) {
            if (e.getStateChange() == ItemEvent.SELECTED) {
                // assume single selection
                int i = (Integer)e.getItemSelectable().getSelectedObjects()[0];
                text.setText("Selected [" + i + "]");
            }
        }
    });