为什么Java ActionListener不起作用？

Question

伙计们,我打算实现一个简单的按钮ActionListener,但它看起来不起作用.java代码附加如下.....程序打算响应用户的点击操作并更改JLabel的上下文

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

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

public class Frame extends JFrame implements ActionListener {

    public JButton btn = new JButton("Click");
    public JLabel display = new JLabel("null");
    public JPanel mainPanel = new JPanel();

    public Frame() {

        mainPanel.add(btn);
        mainPanel.add(display);

        add(mainPanel);
    }

    public void actionPerformed(ActionEvent e) {

        if (e.getSource() == btn) {
            display.setText("it works");
            System.out.println("it works");
        }
    }

    public static void main(String[] args) {

        Frame testFrame = new Frame();
        testFrame.pack();
        testFrame.setVisible(true);

    }
}

Answer 1

您的actionlistener(JFrame本身)未添加addActionListener.

Answer 2

您应该将ActionListner添加到按钮

public Frame(){

    mainPanel.add(btn);
    mainPanel.add(display);
    btn.addActionListener(this);
    add(mainPanel);
}