Ничего не отображается во Frame. Swing

import javax.swing.*;
import java.awt.*;
public class TabbedDemo {
    public static void main(String[] args) {
        String str;
        JFrame frame = new JFrame("TESSTING");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setSize(500, 500);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        JTabbedPane tabbedPane = new JTabbedPane();
        JPanel addPanel = new JPanel();
        addPanel.add(new JLabel("KOKO"));
        addPanel.add(new JButton("KOKO"));
        addPanel.add(new JTextField("KOKO"));
        JPanel updatePanel = new JPanel();
        JPanel deletePanel = new JPanel();
        JPanel showPanel = new JPanel();

        tabbedPane.addTab("ADD", addPanel);
        tabbedPane.addTab("UPDATE",updatePanel);
        tabbedPane.addTab("DELETE",deletePanel);
        tabbedPane.addTab("SHOW",showPanel);
        frame.add(tabbedPane);
    }
}