这里是代码的工作修改。你应该能够按原样运行它。基本上，您不能简单地将 ImageIcon 添加到 JPanel 。您需要首先将其包装在 JLabel 中。

Here's a working modification of your code. You should be able to run it as is. Essentially, you can't simply add the ImageIcon to the JPanel. You need to wrap it in a JLabel first.

import java.awt.BorderLayout;
import java.net.URL;

import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Test2
{
    public static class PanelGlowny extends JPanel
    {

        public PanelGlowny( )
        {

            this.setLayout( new BorderLayout( ) );

            // incorporated @nIcE cOw's comment about loading classpath resources
            URL url = getClass().getResource("logo.jpg")
            ImageIcon imageicon = new ImageIcon( url );
            JLabel label = new JLabel( imageicon );

            this.add( label, BorderLayout.NORTH );

        }
    }

    public static void main( String[] args )
    {
        JFrame frame = new JFrame( );

        frame.add( new PanelGlowny( ) );

        frame.setSize( 400, 400 );

        frame.setVisible( true );
    }

}