在 JFrame 中自动调整 JPanel 的大小

I have a JPanel subclass on which I add buttons, labels, tables, etc. To show on screen it I use JFrame:

MainPanel mainPanel = new MainPanel(); //JPanel subclass

JFrame mainFrame = new JFrame();
mainFrame.setTitle("main window title");
mainFrame.getContentPane().add(mainPanel);
mainFrame.setLocation(100, 100);
mainFrame.pack();
mainFrame.setVisible(true);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

But when I size the window, size of panel don't change. How to make size of panel to be the same as the size of window even if it was resized?

解决方案

You can set a layout manager like BorderLayout and then define more specifically, where your panel should go:

MainPanel mainPanel = new MainPanel();
JFrame mainFrame = new JFrame();
mainFrame.setLayout(new BorderLayout());
mainFrame.add(mainPanel, BorderLayout.CENTER);
mainFrame.pack();
mainFrame.setVisible(true);

This puts the panel into the center area of the frame and lets it grow automatically when resizing the frame.