Java 按下JButton时，JLabel中的文本不会得到更新

我正在做一个项目，但该计划似乎有一个错误，我找不到

下面是一个重现问题的示例：

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;

import java.awt.FlowLayout;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class SO{
    JLabel label;
    JButton button;
    JPanel panel;
    JFrame frame;

    public static void main(String[] args){
        new SO().start();
    }

    public void start()
    {
        label = new JLabel("Button not pressed");
        button = new JButton("Press me");
        frame = new JFrame();
        panel = new JPanel(new FlowLayout(FlowLayout.CENTER));

        panel.add(label);
        panel.add(button);

        frame.add(panel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

        button.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e)
            {
                System.out.println("Button was pressed");
                label = new JLabel("Button is pressed"); //Doesn't work
                frame.repaint();
            }
        });
    }
}

上面的程序有一个带有一些文本的JLabel和一个JButton，它们都被添加到JPanel中，而JPanel又被添加到JFrame中

按下按钮时，我希望JLabel中的文本发生更改。但是文本没有改变，尽管每次我按下按钮时都会执行println

这里有什么问题？

改变

label = new JLabel("Button is pressed");

到

---

您不需要每次都创建和分配新标签。只需更改文本即可

单击按钮即可创建JLabel的新对象，但之后不将其添加到JPanel或JFrame

尽管创建了新对象，即

像这样做

label.setText("Button is pressed");

---

您可以将该行更改为label。按下SetText按钮；让这一切顺利进行

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;

import java.awt.FlowLayout;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class SO{
JLabel label;
JButton button;
JPanel panel;
JFrame frame;

public static void main(String[] args){
    new SO().start();
}

public void start()
{
    label = new JLabel("Button not pressed");
    button = new JButton("Press me");
    frame = new JFrame();
    panel = new JPanel(new FlowLayout(FlowLayout.CENTER));

    panel.add(label);
    panel.add(button);

    frame.add(panel);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

    button.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e)
        {
            System.out.println("Button was pressed");
            label.setText("Button is pressed"); //Doesn't work
            frame.repaint();
        }
    });
}
}

label.settext文本；

label.setText("Button is pressed");

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;

import java.awt.FlowLayout;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class SO{
JLabel label;
JButton button;
JPanel panel;
JFrame frame;

public static void main(String[] args){
    new SO().start();
}

public void start()
{
    label = new JLabel("Button not pressed");
    button = new JButton("Press me");
    frame = new JFrame();
    panel = new JPanel(new FlowLayout(FlowLayout.CENTER));

    panel.add(label);
    panel.add(button);

    frame.add(panel);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

    button.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e)
        {
            System.out.println("Button was pressed");
            label.setText("Button is pressed"); //Doesn't work
            frame.repaint();
        }
    });
}
}