error upon assigning Layout: BoxLayout can't be shared

Question

I have this Java JFrame class, in which I want to use a boxlayout, but I get an error saying java.awt.AWTError: BoxLayout can't be shared. I've seen others with this problem, but they solved it by creating the boxlayout on the contentpane, but that is what I'm doing here. Here's my code:

class EditDialog extends JFrame {
    JTextField title = new JTextField();
    public editDialog() {
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        setTitle("New entity");
        getContentPane().setLayout(
            new BoxLayout(this, BoxLayout.PAGE_AXIS));
        add(title);
        pack();
        setVisible(true);
    }
}

Answer 1

Your problem is that you're creating a BoxLayout for a JFrame (this), but setting it as the layout for a JPanel (getContentPane()). Try:

getContentPane().setLayout(
    new BoxLayout(getContentPane(), BoxLayout.PAGE_AXIS)
);