Java错误：java.lang.IllegalArgumentException：将窗口添加到容器

Question

编程的新手。我正在尝试创建一个简单的交通信号灯。 “面板”需要保留为“ LightShow”对象，但是日食表明我使它成为类型组件。我收到此错误：

  

线程“ main”中的异常java.lang.IllegalArgumentException：向容器添加窗口

at java.desktop/java.awt.Container.checkNotAWindow(Container.java:512)

at java.desktop/java.awt.Container.addImpl(Container.java:1115)

at java.desktop/java.awt.Container.add(Container.java:436)

at guiPpTrafficLights.TrafficLightShow.main(TrafficLightShow.java:15)

//交通信号灯表演班

import javax.swing.JFrame;

public class LightShow extends JFrame
{
    public static void main (String[] args)
    {       
        JFrame frame = new JFrame("Light");

        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

        LightShow panel = new Lightshow();

        ```````````````````````````````````````````````````````````
        frame.getContentPane().add(panel); \\Error happening here.
        ```````````````````````````````````````````````````````````
        frame.pack();
        frame.setVisible(true);
    }
}