Question

I have an array of JLabels, they seem to work. If I do a System.out.print(days[index]); I get the actual information contained and the label is present and works.

When i try to add the label at any index to the panel I’m getting a null pointer exception and I’m not sure why?

public class DrawCalendar extends JPanel{

private JLabel month = new JLabel("Month");
private JLabel[] days = {
    new JLabel("Sunday"),
    new JLabel("Monday"),
    new JLabel("Tuesday"),
    new JLabel("Wednesday"),
    new JLabel("Thursday"),
    new JLabel("Friday"),
    new JLabel("Saturday")
};
    private JPanel dayBoxes;
    private JPanel topLabels;





    public DrawCalendar(int month){

        topLabels.add(days[1]);  //the NullPointerException caused here
        add(topLabels);

    }
}

Answer 1

topLabels hasn’t been instantiated. It is of type JPanel, but it is not a JPanel until

  topLabels = new JPanel();

Until then, it is null.