ActionListener 没有实现

2022-01-24 00:00:00 java actionlistener jframe

JFrameWithPanel 不是抽象的，不会覆盖 java.awt.event.ActionListener 中的抽象方法 actionPerformed(java.awt.event.ActionEvent)公共类 JFrameWithPanel 扩展 JFrame 实现 ActionListener

JFrameWithPanel is not abstract and does not override abstract method actionPerformed(java.awt.event.ActionEvent) in java.awt.event.ActionListener public class JFrameWithPanel extends JFrame implements ActionListener

我没有收到此代码.书籍和 Java 网站告诉我这是该方法的语法，但此错误再次不断出现.

I Don't get this code. Book and Java site tells me this is the syntax for the method, but again this error shows up constantly.

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);

 }
}

后来

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

推荐答案

该类实现了ActionListener 接口.这意味着它必须实现一个方法:

The class implements the ActionListener interface. This means that it must implement a method:

public void actionPerformed(ActionEvent)

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

However, the class definition you've posted does not include this method, hence why you are seeing a compilation error. To fix the code, try adding the following method:

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

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