如何在JFrame中增加自定义JPanel的高度？

import javax.swing.JPanel;

public class CustomPanel extends JPanel {
    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // 在这里绘制自定义的界面元素
    }
}

import javax.swing.JFrame;

public class MainFrame extends JFrame {
    public MainFrame() {
        CustomPanel customPanel = new CustomPanel();
        customPanel.setLayout(null); // 设置布局管理器为null

        // 设置自定义JPanel的位置和大小
        customPanel.setBounds(0, 0, getWidth(), getHeight());

        // 添加自定义JPanel到JFrame中
        add(customPanel);
    }

    public static void main(String[] args) {
        MainFrame frame = new MainFrame();
        frame.setSize(800, 600);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}