如何在JFrame中放置1个JPanel和1个自定义JPanel

JFrame frame = new JFrame("JFrame示例");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(800, 600);

JPanel panel1 = new JPanel();
panel1.setBackground(Color.WHITE);
panel1.setPreferredSize(new Dimension(400, 300));

class CustomPanel extends JPanel {
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // 在这里进行自定义绘制操作
    }
}

CustomPanel panel2 = new CustomPanel();
panel2.setPreferredSize(new Dimension(400, 300));

frame.getContentPane().setLayout(new FlowLayout());
frame.getContentPane().add(panel1);
frame.getContentPane().add(panel2);

frame.setVisible(true);