Java，单击更改JLabel文本

Question

我是这个网站和Java编程的新手，我非常感谢一些帮助。我正在尝试使用SWING创建一个非常简单的程序，用户单击一个按钮，标签的文本从“Hello”变为“Bonjour”。这是我得到的两个错误：

java:6: error: Lab4Part1 is not abstract and does not override abstract 
method actionPerformed(ActionEvent) in ActionListener
public class Lab4Part1 extends JFrame implements ActionListener {

java:25: error: cannot find symbol
label.setText("Bonjour");

有任何想法吗？我的代码在这里：

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

    public class Lab4Part1 extends JFrame implements ActionListener {

    public Lab4Part1() {
        super("Lab 4 Part 1");
        Container contentPane = getContentPane();
        JPanel panel = new JPanel();
        contentPane.add(panel);
        setSize(400, 100);
        setVisible(true);

            JLabel label = new JLabel("Hello");
            panel.add(label);

            JButton button = new JButton("Translate to French");
            panel.add(button);
            button.addActionListener(this);
    }

    public void handle(ActionEvent event) {
    label.setText("Bonjour");
    }

    public static void main(String[] args) {
        Lab4Part1 myFrame = new Lab4Part1();
        myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    }

Answer 1

您必须直接在类中声明JLabel，以便可以从handle函数访问它：

public class Lab4Part1 extends JFrame implements ActionListener {      

JLabel label; 

public Lab4Part1() {
    super("Lab 4 Part 1");
    Container contentPane = getContentPane();
    JPanel panel = new JPanel();
    contentPane.add(panel);
    setSize(400, 100);
    setVisible(true);

        label = new JLabel("Hello");
        panel.add(label);

        JButton button = new JButton("Translate to French");
        panel.add(button);
        button.addActionListener(this);
}

public void handle(ActionEvent event) {
label.setText("Bonjour");
}