我正在學(xué)習(xí) java swing，這對(duì)我來(lái)說(shuō)很困惑。不顯示退出按鈕。但是，如果我將代碼部分移到textArea按鈕的兩部分之后，它將正確顯示。所以為什么？package exercise1;import javax.swing.*;import java.awt.*;public class ChatClient {    private JTextArea textArea;    private JTextField textField;    private JButton btnSend;    private JButton btnQuit;    private JFrame frame;    private JPanel panel;    private JScrollPane scrollPane;    private void launchFrame() {        panel = new JPanel(new GridBagLayout());        GridBagConstraints c = new GridBagConstraints();        textArea = new JTextArea(10, 50);        scrollPane = new JScrollPane(textArea);        c.gridx = 0;        c.gridy = 0;        c.gridheight = 3;        panel.add(scrollPane, c);        btnSend = new JButton("Send");        c.gridx = 1;        c.gridy = 0;        c.anchor = GridBagConstraints.NORTH;        panel.add(btnSend, c);        btnQuit = new JButton("Quit");        c.gridx = 1;        c.gridy = 1;        c.anchor = GridBagConstraints.NORTH;        panel.add(btnQuit, c);    }    protected ChatClient() {        frame = new JFrame("Chat Room");        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        launchFrame();        frame.add(panel);        frame.pack();        frame.setVisible(true);    }    public static void main(String[] args) {        ChatClient client = new ChatClient();    }}