Why are the items not showing?

Question

Java

I have the following code

public add(){
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        setLocationRelativeTo(null);
        setSize(new Dimension(400, 200));
        setTitle("Add");
        setLayout(new FlowLayout());

        JTextPane jTextPane = new JTextPane();
        jTextPane.setPreferredSize(new Dimension(390, 100));

        JButton jButton = new JButton("добавить");
        jButton.setPreferredSize(new Dimension(200, 30));

        add(jTextPane);
        add(jButton);

        setVisible(true);

    }

But the result is this
. There are still windows, the code is the same, everything is fine there.

Answer 1

Issue resolved

setVisible(true);

add(jTextPane);
        add(jButton);

Thus, it is displayed normally, although a little and not logically.