无法添加ActionListener来添加组件

Question

Supposing that I want to click a button, then a JLabel/JTextArea/... will show in the GUI, how to finish the job?

Example code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class MyJFrame extends JFrame {
    public MyJFrame() {
        JButton jButton = new JButton();
        jButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                add(new JLabel("xxxxx"), BorderLayout.SOUTH);
            }
        });

        add(jButton, BorderLayout.CENTER);
    }

    public static void main(String[] args) {
        MyJFrame myJFrame = new MyJFrame();
        myJFrame.pack();
        myJFrame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        myJFrame.setVisible(true);
        myJFrame.setLocationRelativeTo(null);
    }
}

My code has something wrong. After I clicked the button, there is no JLabel show up.

---

update：

Could anyone tell me what if I want to solve my problem from java official information, where should I search? It seems JAVA tutorial or API have nothing relating with my question..

Answer 1

You should notify the frame that its content has changed ( revalidate() ), and to repaint itself ( repaint() ) :

public void actionPerformed(ActionEvent e) {
                add(new JLabel("xxxxx"), BorderLayout.SOUTH);
                revalidate();
                repaint();
            }