为什么不能在两个内部类上实现两个ActionListener？

Question

I'm doing the double actionlistener exercise detailed in Head First Java, and learn about inner classes, but for some reason my code is not compiling. I'm getting argument invalid errors when I try to call the addActionListener method for JButton.

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: (no errors)

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

You need to import ActionEvent and ActionListener :

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

They reside under java.awt.event.* and not java.awt.* .

If you use an IDE like Eclipse, you can easily import all needed classes with a simple action.