通过按钮更改标签（Java / Swing问题）

这里是新手程序员：

我刚刚按下了第一个按钮。我希望按钮更改标签 Hello World！。到你好宇宙！。我尝试通过 public void actionPerformed（ActionEvent e）寻找更改标签的方法，但未找到任何方法。如果有人愿意向我解释如何更改 public void actionPerformed（ActionEvent e）中的注释部分以更改标签，请解释！

I just made my first button. I want the button to change the label "Hello World!" to "Hello Universe!". I tried searching for ways to change the label through public void actionPerformed(ActionEvent e), but failed to find any. If anybody would be kind enough to explain to me how to change the commented section in public void actionPerformed(ActionEvent e) to change the label, please explain!

谢谢！

我的代码：

package game;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Javagame extends JPanel implements ActionListener{
    double x=Math.random()*500;
    double y=Math.random()*500;
    protected JButton b1;
    public Javagame() {
        b1 = new JButton("Button!");
        b1.setActionCommand("change");

        b1.addActionListener(this);
        add(b1);
    }
    public void actionPerformed(ActionEvent e) {
        if ("change".equals(e.getActionCommand())) {
            //I want a code here that changes "Hello World" to "Hello Universe". Thank you.
        }
    }
    private static void createWindow(){
        JFrame frame = new JFrame("Javagame");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(500,500));

        JLabel label = new JLabel("Hello World!", SwingConstants.CENTER);
        label.setFont(new Font("Arial", Font.BOLD, 20));
        label.setForeground(new Color(0x009900));

        Javagame newContentPane = new Javagame();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);
        frame.getContentPane().add(label, BorderLayout.CENTER);

        frame.setLocationRelativeTo(null);
        frame.pack();
        frame.setVisible(true);
    }
    public static void main(String[] args) {
        createWindow();
    }
}