未知符號的ActionListener

Question

我想要編譯這個類：

import javax.swing.*; 
import java.awt.*; 
import java.awt.event.*; 
import java.awt.event.ActionListener; 
import java.awt.event.ActionEvent; 
public class Main implements ActionListener { 
    private static JFrame frm = new JFrame(); 
    private static JLabel username = new JLabel("User:"); 
    private static JLabel password = new JLabel("Pass:"); 
    private static JTextField username_field = new JTextField(); 
    private static JPasswordField password_field = new JPasswordField(); 
    private static ButtonGroup bg = new ButtonGroup(); 
    private static JCheckBox sp = new JCheckBox ("Singleplayer"); 
    private static JCheckBox mp = new JCheckBox("Multiplayer"); 
    private static JButton play = new JButton("Play"); 
    private static JPanel p = new JPanel(); 

    public static void main(String[] args) { 
     new Main().initFrame(); 
    } 
    public void initFrame() { 
     //Init Frame Stuff 
    } 
    public void actionPerformed(ActionEvent evt) { 
     if (evt.getActionCommand().equals("play")) { 
      //Other Stuff 
     } 
    } 
} 

正如你看到的上面，我已經進口的ActionListener，但如果我編譯代碼我得到一個未知的符號錯誤：

.\GamePanel.java:3: error: cannot find symbol 
public class GamePanel extends JPanel implements ActionListener { 
symbol: class ActionListener 
1 error 

爲什麼我得到這個錯誤？

Answer 1

對於特定的錯誤，您必須導入相關的包。添加

import java.awt.event.ActionListener; 

文件GamePanel.java中，類聲明，即前public class GamePanel extends JPanel implements ActionListener {