我试图做出如下所示的布局。但是我有一个新的MyPanels的门廊。第一个MyPanel填充它的所有父级(midPanel)。如何使MyPanel只取所需的高度和填充宽度?
public class Main extends JFrame {
JPanel upPanel = new JPanel();
JPanel midPanel = new JPanel();
JPanel downPanel = new JPanel();
JButton button = new JButton("add new Panel");
Main() {
this.set