爲什麼我不能在兩個內部類上實現兩個ActionListener？

Question

我正在做Head First Java中詳細介紹的double actionlistener練習，並瞭解內部類，但由於某種原因，我的代碼沒有編譯。當我嘗試爲JButton調用addActionListener方法時，我得到的參數無效錯誤。

TwoButtons.java：

import javax.swing.*; 
import java.awt.*; 

public class TwoButtons { 
    JFrame frame; 
    JLabel label; 

    public static void main(String[] args){ 
     TwoButtons gui = new TwoButtons(); 
     gui.go(); 
    } 

    public void go(){ 
     frame = new JFrame(); 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

     JButton labelButton = new JButton("Change Label"); 
     labelButton.addActionListener(new LabelListener()); 

     JButton colorButton = new JButton("Change circle"); 
     colorButton.addActionListener(new ColorListener()); 

     label = new JLabel("I'm a label"); 
     MyDrawPanel drawPanel = new MyDrawPanel(); 

     frame.getContentPane().add(BorderLayout.SOUTH, colorButton); 
     frame.getContentPane().add(BorderLayout.CENTER, drawPanel); 
     frame.getContentPane().add(BorderLayout.EAST, labelButton); 
     frame.getContentPane().add(BorderLayout.WEST, label); 

     frame.setSize(300,300); 
     frame.setVisible(true); 

    } 

    class LabelListener implements ActionListener{ 
     public void actionPerformed(ActionEvent event){ 
      label.setText("OUch!"); 
     } 
    }//close inner class 

    class ColorListener implements ActionListener{ 
     public void actionPerformed(ActionEvent event){ 
      frame.repaint(); 
     } 
    } //close inner class 

} 

MyDrawPanel.java：（沒有錯誤）

import java.awt.*; 
import javax.swing.*; 


public class MyDrawPanel extends JPanel{ 
    public void paintComponent(Graphics g){ 
     Graphics2D g2d = (Graphics2D) g; 

     int red = (int)(Math.random()*255); 
     int green = (int)(Math.random()*255); 
     int blue = (int)(Math.random() * 255); 
     Color startColor = new Color(red,green,blue); 

     red = (int)(Math.random()*255); 
     green = (int)(Math.random()*255); 
     blue = (int)(Math.random() * 255); 
     Color endColor = new Color(red, green, blue); 

     GradientPaint gradient = new GradientPaint(70,70, startColor, 150,150, endColor); 
     g2d.setPaint(gradient); 
     g2d.fillOval(70, 70, 100, 100); 

    } 

} 

Answer 1

您需要導入ActionEvent和ActionListener：

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

他們住java.awt.event.*下和而不是java.awt.*。

如果您使用Eclipse之類的IDE，則可以通過簡單的操作輕鬆導入所有需要的類。