ActionListener未实现

Question

JFrameWithPanel不是抽象的，并且不会重写java.awt.event.ActionListener公共类中的抽象方法actionPerformed（java.awt.event.ActionEvent）JFrameWithPanel扩展了JFrame实现ActionListener

我没有得到这个代码。Book and Java网站告诉我这是该方法的语法，但是此错误再次不断出现。

import javax.swing.*;
import javax.swing.JOptionPane;
import java.awt.*;
import java.awt.event.*;
import java.lang.Math.*;
import java.lang.Integer.*;
import java.util.*;
import java.util.Random;
import java.io.*;
import java.text.*;
import java.text.DecimalFormat.*;

public class JFrameWithPanel extends JFrame implements ActionListener
{
 JButton button = new JButton("Exit");

 public JFrameWithPanel()
 {
  super("JFrame with Panel");

  JComboBox packageChoice = new JComboBox();
  packageChoice.addItem("A+ Certification");
  packageChoice.addItem("Network+ Certification ");
  packageChoice.addItem("Security+ Certifictation");
  packageChoice.addItem("CIT Full Test Package");

  packageChoice.addActionListener(this);

  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  JPanel pane = new JPanel();
  pane.add(button);
  pane.add(packageChoice);
  setContentPane(pane);
  setSize(200,100);
  setVisible(true);

 }
}

然后再

public class CreateJFrameWithPanel
{
 public static void main(String[] args)
 {
  JFrameWithPanel panel = new JFrameWithPanel();
 }
}

Answer 1

该类实现ActionListener接口。这意味着它必须实现一个方法：

public void actionPerformed(ActionEvent)

但是，您发布的类定义不包含此方法，因此为什么您会看到编译错误。要修复代码，请尝试添加以下方法：

public void actionPerformed(ActionEvent evt) {
  Object obj = packageChoice.getSelectedItem();
  JOptionPane.showMessageDialog(this, "You selected: " + obj);
}